That was informative. But, I was hoping for more info on . 1. How does "rocker" in hull design profile, affect dynamic drag (suction) by vertical or rocking movement of the hull? 2. How does depth of hull affect drag vs displacement? eg. comparing a "V" cross-section having the same displacement as a wide curved but flatter hull cross-secton. Taking into account wetted surface influence 3. How does hull symmetry along the hull centreline affect performance & drag? eg. What if the centerline is not along the centre of the beam but more to the outboard of each hull. Making a wider distance between the centrelines of the two hulls. 4. Are the Port & Starboard hulls both pulled from the same mold?
I think this comes down to what are your priorities. (Not disputing the analysis, the engineer did a great job of presenting the design/performance theory). Is your priority to sail as quickly as possible? Are you buying a yacht to experience the maximum sailing performance? Are you looking for maximum comfort? Are you looking for minimum draft? If you are looking for performance, are dagger boards a requirement? Etc. This seems to suggest its like Americas Cup and the fastest boat wins. For some this may be accurate, for others its more about the experience of travel and adventure. At one time on early Ruby Rose video’s I remember hearing only a monohull was the preferred sailing vessel. We all watch several sailing channels and obviously the journey is accomplished in MANY different ways. They all seem to achieve their individual objective. I have two cars. One is a GMC Suburban and the other is 911 Porsche. Both will allow be to drive from California to New York however, (and as with everything) there will be tradeoffs. For me my goal is to travel and share an adventure of a lifetime and much less about the design of the yacht. It seems to me The Wynns, UMA, SLV, Delos, O’Kelly’s etc. are all out sailing and achieving their dreams. For me this is the most important criteria.
dagger boards dramatically reduce lee drift. your sliding sideways without danger boards, and then your course "made good" suffers....point a to point b , what is performance?.....but you honestly don't need dagger boards on a Hobbie 16, because it has a low prismatic coefficient .... so big cruiser cats need dagger boards, where only light beach cats don't.
mono hull keel boats are the most sea worthy ... you don't want to flip a cat ... I guess some of the big heavy cats won't, but that goes back to making the hull lift work for the design ... different cats are designed different for the reasons that they where designed to be what they are .... so if your not a designer, just pick that works for you.
Several years ago I read a book from the 1890's on steam locomotive design and was quite surprised at how much the engineering was based on ratios. Ex. If a part for a certain function needs to be X inches long then it needs to be at least X/12 inches thick. These ratios were derived from what worked in the field and what didn't work rather than from material science and complex maths. Although we now have computers which can perform hydrodynamic calculations in fractions of a second it is interesting to me that we still use ratios when talking about the properties of a boat.
As an Ocean/Naval Engineering student, this is a fantastic exchange of information within the industry. I'd consider myself a customer more concerned with technical aspects rather than the lush and plush stuffed in.
To be straight up, I was worried about getting something less than this, dare I say it im looking forward to it now. Congrats on the new boat, sure your looking forward to it. I remember saying no rush on announcing it as long as you went into all the technical details like you said you were going to. Now you have set the bar high, keeping your word, I like it. You have me looking forward to the rest of this series. Thankyou, in depth technical stuff, if you can do this on everything its bloody awesome. Everyone else does drooling over double sinks and different fabrics and bar areas. This is what I am after myself. Thankyou Terysa for putting up with him while he delivers this content :P.
Please keep banging on about this stuff!! And a hearty congratulations for finding the yacht for your needs! I'm a year into research for finding a catamaran for a currently non-sailing couple retiring in a few years time. Finding opinions like 'performance cruising catamaran' and 'usable living space' is easy. But, finding any detailed facts about the science behind this is very difficult. With very little digging, I can easily know almost all of the dimensions and performance specifications regarding my laptop computer and all of its internal components. And all that info for a small machine that costs only a few thousand dollars! But, it seems catamaran manufacturers expect us to spend hundreds of thousands of dollars, if not millions, on the vessels they produce, while telling us very little about what actually makes them tick. I get the feeling they hope to sell us on the romance of the adventure without wanting us to really know what the vessel can and cannot do. With all machines, I am very, very interested in what they cannot do. That knowledge is what allows us to make decisions that keep us safely in the 'can do' zone. And when buying used, there seems to be even less information available. So please do keep banging on about this stuff!
Always liked your show. I think there was a typo though. Slenderness ratio is LWL/(HVol)^1/3, the higher the faster, not the other way around. Nowadays mostly the weight+Length+sails determines boat performance. I liked seawind 1260, but the cabin ceiling too low to be comfort. Seems like Seawind 1370 improved. Looking forward to more info on pricing etc.
for some reason I can seem to figure out what prismatic coefficient is and how it affects performance/comfort. they showed a chart but then went on to the next aspect affecting hull performance/comfort. that being said, I've seen vids of people sailing cats and complaining that the waves "slap" the hulls or the bridge deck and now I understand why. they probably had it overloaded or design was so that the bow waves were crossing into the bridge deck and or hitting the opposite hull. (no idea what cat it was) very informative and interesting. Thank you.
The way I design hulls is to choose a fish that encapsulates the boats personality, the bottom half of that fish is now your hull design below the waterline. :)
LOVE the more technical information. It's something that seems really lacking on the net in any real organized way. Everyone just says "go read The Principles of Yacht Design" which I plan on, but it would be nice if there was an organized repository of this knowledge for those of us who learn better that way than reading whole books of dry information.
Slenderness ratio = Length / Hull Volume. The formula at 8:00 is the DLR (Displacement Length Ratio), which is inversely proportional to the Slenderness ratio. Also the SR is in SI units, the DLR in Imperial units. Since he is talking about actual numbers this is relevant.
These statistics are for the under water portion of hulls. Very little, if any, of a cruising sailboat interior is under water. Waterline beam plus flam determines the interior more than any technical statistic.
Interesting info Nick and it's good top know these things thanks. But will the Prismatic Coefficient really be a factor to discuss for anyone buying a family cruiser, It's a bit slower but we can shower, keep the beer and wine chilled and will get less wet would be the selling point I think. I'd loved to know how they work out the position to place the mast for optimal performance, who decides that it goes further aft or toward the bow for better upwind or down wind sailing. Hopefully you will have that come up in one of your videos.
This is my new Favorite Playlist from Ruby Rose. So many things I am thinking about but just dont seem to be talked about in an approachable fashion. Looking forward to more.
Very good wish I had this info in 89 when I started building my Simpson 12m I would have gone on a diet! Cruised it for 20 years so I must have done something right
Interesting. One shape to consider is hull asymmetry. When viewed from above, a Hobie 16's hull has an airfoil shape: the hull is flat on the outside but curved on the inside. The idea is that it co.pensates for lack of a centerboard: it generates lift for windward performance and reduces leeward drift by presenting a flat surface to the water on the outboard hull. Do modern cruising cats do this?
Yes, my new hull design does. It is an improvement on the Hobie design hull. I have tested many 5m prototype hulls and compared to conventional modern dagger board hulls, the results show advantages which are; Superior lateral resistance at all speeds. High and low speed efficiency without foils. Excellent sea keeping capabilities. Cheers
Nice work on this video! I was told this series is worth a look and it sure is. I believe style on a lot of new performance cruisers is still being put before cruising function quite a bit. Immersed transoms is a great example of racing style looking cool but not functional for cruising. The wider shorter sterns with immersed transoms only offer more performance once at high speed. They are slower in light air and for performance cruising light air performance is actually more important than a few % more at the top end when your likely slowing down anyway. If you have anti foul pain on your transom you have wet heels... Mick
Helo miss, i am a part of an undergraduate student team of Naval Architecture, who is participating in Ferry design compettition , we are designing a catamaran and we require the range of coefficients best for catamaran for e.g Cb ,Cp LBr e.t.c. so we request you to help us in any way you can for that. Thanks a lot.
My own view is that if one is after a performance catamaran stick with something over fifty feet, otherwise it's too much of a battle between narrow hulls and comfort.
I’m not currently not a Blow-Boater but this discussion was fascinating for me. Cat’s have become more and more popular on the Power Boat scene and I am currently thinking about “next” for us and whether to go cat or Knot... (with focus on comfort versus performance) so even for a Motor Head this was an exceptional vid... looking forward to the rest of this discussion!
That makes so much sense now, in fact it`s why I binned my first missus all those years ago! Over time, her slenderness ratio decreased to the point it dramatically reduced performance and as her wetted surface area increased it had a negative impact on speed, comfort etc and I had to have her bottom scraped more often. Seriously, thanks Nick, I did enjoy this first foray into the design process and look forward to more of the same , cheers easy.
That was informative. We never hear anything about hull design, if you want to know you have to go looking. Other important factors that effect slamming are the distance from the bow to where the bridge deck starts and the shape of the leading edge of the bridge deck. Having the hull shape with a flat section in the stern helps reduce hobby horsing. The charter industry has turned cats into max volume to minimum length boats, at the detriment of sailing ability. What is called a performance cat today is really just a well designed cat that should sail well in all conditions. Cats with all lines led to a single helm with 2 winches and a bank of jammers would have been considered suicide 30 years ago, today it's just a cheap option for under powered cats. If you are interested in buying a cat it's best to sail on as many different brands/designs as possible, there is no substitute for experience. Cheers Rustie.
Lad might not look as if he has started shaving yet, but he knows his stuff! Still not convinced hull shape would influence my future choice of Cat. Key would be not to overload even a slower cruising cat, but price will be the main factor for me, and in the used market you can get a cheaper FP, Lagoon or Leopard that is still a great safe boat that will cross oceans.(steadily not speedily) I could not get the wife to agree to live aboard a performance cat with narrow hulls. If what your research pans out, Seawind seem to be trying to find a sweet spot between cruising & performance. Hope it does not end in the middle doing neither particularly well, but don't think it will, your future Cat looks awesome, with above average cruising & liveaboard comfort and good potential performance. Looking forward to watching your journey & logging all the lessons learnt for mine!
Exactly that mate! There are a few old salts on here who seem to think that to have any credibility in the sailing world you have to have skin like sandpaper and a beard you can hide a badger in
For customers that will spend big money on a Catamaran, I would think they spend a lot of time going over this type of information. But I think everyone knows most buyers just go for the boat that has a nice finish and a great sound system. The science behind fluid dynamics regarding lift and resistance in the water is the most important. Thank's for a great look into a small but complex part of Catamaran design.
2 ปีที่แล้ว
This information is not usually readily available.
Tony & Susan here, Thank you so much for including us in your detailed discussions with the designer. I am kind of a geek . And am always interested in the details. Susan would love to see the interior design and colors and plates and glasses. Cheers
What you need to know about a boat to make a well-informed buying decision are all the things you can NOT change. So yes, the hull ratios and shapes are way more relevant than the number of fabrics for the saloon, the size of the winches or the controller of the electrical power system (just to name a few).
You could have asked once you have arrived at your final design what is the additional ‘TPI’ (tonnes per inch immersion) if at DWL. To be honest the basic waterline is an academic (although necessary design datum) I would insist that the DWL includes - All tanks including holding tanks at 95% full, specified dinghy and outboard weight, life raft, specified anchor cable and anchor (otherwise they will ‘short chain’ you😉), solar panels and associated control gear and invertors, an allowance for engineering stores (fluids) and spare gear, Weight of passengers- if boat licence for 6 or 8 so be it - with luggage allowance (say 40 kilos each), food and provisions for certified number of passengers for 3 weeks. If the DWL then compromises the key numbers including bridge deck clearance then the NA has to ‘go round the buoy’ and iterate hull form to achieve the objective. Good vid.😀👍⛵️
2 ปีที่แล้ว
Half full tanks are usually used in displacement calculation.
I'd love to pick his brains myself. Great interview choice. I've always wondered what made the great clippers so fast and just what the architects of the day knew and how that knowledge is applied today.
As with any product, they are designed for the customers. If the customers are more technically savvy then the catamaran companies will pay more attention to these details. Videos like this are great for promoting good design. I am becoming familiar with these ratios and fluid dynamics because of a more humble project. I am trying to design and build an ultra-lightweight (
Great video, love how you get into the tech sides of the boats instead of just the shiny stuff. A discussion on hull performance rating to rig performance would be a great follow up video. Keep up the great vids!
This really helped me understanding engineering behind the catamarans, as i am a design graduate taking part in a design competition with no idea about boats and how they work, this was very informative !
Helo sir, i am a part of an undergraduate student team of Naval Architecture, who is participating in Ferry design compettition , we are designing a catamaran and we require the range of coefficients (e.g 0.345-0.5)best for catamaran for e.g Cb ,Cp LBr e.t.c. so we request you to help us in any way you can for that. Thanks a lot.
GREAT show, waiting in anticipation for the next installment of this series, learnt a hell of a lot from this episode, thanks for bringing in the naval architect to explain this in more detail
I enjoyed this immensely, getting a Bali 5.4 (6 cabins ) by Catana, for business. I need volume, that so much performance, plus structural strength is important to me.
I think you are growing into becoming a true catamaran design analyst! I’m like probably the vast majority of your viewers became excited watching this video about your venture into opening the pandora box of hull/boat design science. You are doing an outstanding job in educating us about the various hull design features impacting performance and comfort. Understanding and awareness of the hull features of your boat has also an undeniable positiv impact in managing the boat more safely by knowing the range and limits of its capabilities! I truly love what you do and the way you go about educating us and most important handing us the tools to understand boat design. Job very well done! A BIG THANK YOU, keep on going, excited to see what’s coming next!
Thanks for the interesting interview. I couldn't get the slenderness ratio that was written on one of your blackboards to work out. So, after a little research I found this equation which seems to be correct. SR=Lwl/Vol^0.333 ; SI units
Great video. A lot of different terms like drag and displacement and such were thrown around a lot without a lot of context on what they actually are and how important they are to the overall performance. I'm less clear what drag is on a hull and how much it effects performance but I can define displacement. Everything knows what it is, but they don't understand why it's so important. If you had a boat sitting in the water and you froze time and removed the boat, the volume of the hole left in the water is the displacement. Multiplied by the weight of water is the weight of the boat. Displacement is important when you start moving because you have to push water out of the way to make a "new" hole in the water. How much effort this takes depends on how much water and how far you need to move it to make the hole per second. This is why cats are faster than mono hulls. If they have the same displacement, the cat has to move the water half the distance to make the hole it needs.
@ You slightly misunderstood me. What I described wasn't just about the volume of water but also the distance you need to move it. Longer narrower hull with the same total displacement will be significantly faster. Split a single hull into multiple while keeping the same volume of displaced water and it will be significantly faster because the water has half the distance it needs to move. While there are other factors, this is by far the overriding factor to start with.
Good start Nick. Diagrams are pretty iffy - don’t just uncover a picture of a cat and gloss over - it’s not hard to draw them properly. Look over what Hanneke did with James years ago for inspiration. Some of Tennant’s and Shuttleworth’s are good too. It’ll make things much better to voice over the diagram. Also a slenderness of 7 is pretty ridiculous for a cruising boat - that is less than 10tonne displacement for a 15m/50’ cat! Even if - huge if - the manufacturer can have it leave the yard less than 10tonne, there is no way it will stay under once you cruise. So I think the number he’s chosen doesn’t reflect raising reality in any shape or form and that makes me wonder about other points he makes (although there were no other actual numbers which itself is interesting - is the architect for Seawind going to point out that a length to beam of 8-9 is low if their boat has it?)
Actually, thinking further, I suggest a good chat with Rob Denney of Harry proa “fame” will provide a much needed different perspective of experienced practical multihull development. Terysa can find him in WA usually...
You must realize, it is almost guaranteed that the entire series was filmed some time ago. For one, Nick is in the study room of his parent's home, whereas Nick and Terysa have been back onboard Ruby Rose for some time. Knowing anything from watching these two for more than a couple tech episodes, one would discover that Nick is quite particular and thorough with his research. So, many questions will most likely be answered in the series, but most likely will draw more questions one should then venture into their own research and preferences to address. 🤙
2 ปีที่แล้ว
Small cruising catamarans usually have a hull L/B of 8 or so. Larger ones will have 8 to 12, depending on the priorities of the designer for the design. 12 is fast, 8 is roomy.
Right up my street, I have a slight advantage as I studied stability at south tyne side marine college and found this very interesting. In my opinion I would have dagger boards due to 9 x out of 10 I'm always sailing to windward.
I've just put the euro lottery on, its £42 million, after watching all of your you tube videos on cats I'll be purchasing one, with that kind of cash I could go OTT on a yacht but any thing over 55ft is a waste for two people in my opinion 🚣♂️🚣♂️🚣♂️🚣♂️🚣♂️
Interesting. But, one important consideration that was addressed but passed over very quickly, is the law of buoyancy or Archimedes principal. Regardless of the ratios that impact performance and lift at speed (i.e. dynamic performance), one has to understand that for any given weight of boat and load, the volumetric displacement of the hull will be the same. Archimedes Principal basically states that the weight of, in this case, a fully loaded boat, will have to displace the volume of water of that same weight. In other words, a cruising boat or a performance boat of the same weight, will have to have the same volume of hull below the waterline (i.e. the volumetric displacement will be equal). That is why, I am assuming that performance boats have to be lighter which is intuitive, but also required, because narrower hull for any given length of boat will have has less volumetric displacement therefore, will only support a lighter fully loaded boat. Therefore hull DISPLACEMENT will always be directly related to the boat weight.
correct, but that's the whole issue, these superficial videos about hull design never really expose the impacts of specific design decisions. They cover generalities and make the viewer believe they understand better. They do not. All they should understand is that is the topic way more complicated than they understand. Engineering is hard. Dunning-Kruger is real. To carry a specific load (boat + gear + people) It is not the displacement that is important, it is the shape of that displacement and the vast tradeoffs in that shape design...
@ My point was simply that in my experience many people don't know the law of buoyancy - it isn't necessarily common knowledge and it wasn't explicitly explained in the video. So, I was just pointing out that for any given designed displacement or weight of a boat, that in itself, will define the displacement of the hull (or the volume of hull that is below the waterline). So, it you want the hulls to be narrower, then they will have to be longer or conversely if you to the length of hulls to be shorter, than the hulls will have to be wider. In other words, from a design perspective, if someone wants to build a boat that fully loaded is say 20 tons and they also want it to be no more than 45m long, than the choice of how wide the hulls are be will not be much of a choice, as the hulls will have to be as wide as they need to be at 45m long to displace a volume below the water line that equal to 20tons of water. More simply, if someone had a row boat and wanted to know how much weight it could carry, then they could put it on a scale and weigh it and then fill it full of water to the point that water is spilling over the gunnels. Take that total weight and subtract the weight of the boat and the result is how much it can carry before it sinks.
Beautiful the scenery is so beautiful and stunning.Very enjoyable! Reminds me of my trips where I take the good music like the Guns N Roses, Imagine Draongs or the Delta Parole and then enjoy the powerful feeling of the sea. ¡vamos!
"Vertical dynamic lift" Is that also called 'planing'? (Factoid: The Aleuts were planing at about 8 knots and could sustain 10 knots over distance. This was reported by Captain Cook's navigator, probably the best technical source available in the 18th century. Maps they made of New Zealand were used into World War Two). Loading the boat. I'm a terrible backpacker. Some backpackers walk thousands of mile and their backpacks never exceed 20 lbs. Me 4-5 days 50 lbs. However, I weigh everything, make a spreadsheet, sweat every ounce - otherwise my pack would be 80 lbs. I don't think cruisers get this extreme, but I'll bet a couple of good scales, a spreadsheet and some obsessiveness would shave a lot of excess weight and also point out where it is. Instead of canned goods maybe another freezer might give you more and better vegetables at less weight - just maybe, I have no experience (yet). Great series. Probably going to save me a lot of money, and a lot of disappointment when I buy a multihull.
my preferred concept...how fast can I make this thing go, comfort be damned! These engineering concepts and detailed analysis, is also applicable to automotive design. I want to know spring rates, alignment specs, tire specs, and all the pedantic details. As an enthusiast, I love this analysis series!
Except that the tyres, suspension and bushes are not just for the driver but for the vehicle. Comfort plays a role in speed, if the ride is harsh it puts a lot of stress on the hull/chassis, which means they need to be stronger, which means more weight. Engineering is fun. Just think of why F1 cars still have suspension.
Interesting information. Do mfg’s publish the empty weight (leaving the factory) and the useful load? This is done with airplanes. 2 tons is not a lot of weight especially if the boat is not fully outfitted with cruising gear. Generators, dingy (with motor ) water makers, various sails. The list goes on... then there is the Pabst Blue Ribbon too!
Yes, boat designs are quoted in light displacement, which is nearly empty and loaded displacement, which includes full fuel, water, supplies, people, etc. There's also something in between which is often called normal displacement, sort of a typical value. Similar idea to aircraft, for similar reasons.
2 ปีที่แล้ว
It is hard to get technical information for retail product boats of any kind.
For performance yes, cruising I'd disagree. When you kiss the bottom with daggerboards you snap stuff off, and potentially bust up your sail drive and rudders. Mini keels protect all that and if done right can still offer some performance. Seawinds 1160 and 1260 models are mini keeled and perform well
Interesting interview, thanks for putting it together. These concepts are of course interesting, but in the end the most useful tool to assess the performance of a boat are its polars right? They factor in all the aspects including water and air drag, the size of the sails, their interactions, the static and dynamic righting moment (for boats that generate some), the impact of heeling (less relevant for catamarans), the ability to plane,... It's next to impossible to anticipate the resulting performance from considering isolated aspects even if yes, a more narrow hull will typically mean more speed. This being said, when you watch videos of the recent Vendee Arctique, it seems clear that performance is just part of the story for passage mating. I would argue that comfort is also key and that is probably even harder to assess from isolated boat characteristics than performance. Speaking about monohulls, one rather unintuitive thing I learned recently is that boats with lifting centerboards are often more comfortable at anchor (less motion) compared to those with lifting keels, because the centerboarders are designed to have balast independantly of the weight of the keel, so they remain stable even with the centerboard up. This to say that considering only the performance value of a keel would result in overlooking this essential aspect of comfort at anchor.
2 ปีที่แล้ว
Sailing catamarans don't have ballast. It is widely agreed that weight is the biggest determiner of sailing catamaran speed.
great discussion, I would however suggest you have (like any of us would after making a boat buying decision) a bias towards a certain design which is steering the discussion. The several times said "there are no bad boat designs just different intentions" (paraphrased a bit) should be talked about much further because it is all compromise and we are just looking for our ideal compromise (not just yours). Objectivity would show for each feature that might compromise speed could add comfort so in a so forth through all of your excellent talking points. It is also important to frame this discussion with the scale of actual differences in sailing performance. My point being that is you watch the ARC races (for example) there are plenty of well skippered "condomarans" finishing well up the order every single year. Yes it's won by a Gunboat but there are plenty of Lagoons and FP's in front of and intermingled with the "performance" cats. That is because other factors have a bigger bearing on performance than simply hull design. It would be cool to talk about these real world influences at some point with objectivity and holistically look at the realities of getting from point A to point B (circumnavigation: Point A to Point A!) with the perfect blend of speed AND comfort for different types of sailers (and sometimes queasy reluctant crew). Your Naval Architect wants to say it but you won't let him because you keep steering the conversation towards performance being the answer
2 ปีที่แล้ว
Boats should be designed for their intended use, but bad designs do exist, I'm afraid. Alas, the average boat is designed to please wives who are thinking of short family vacations, with accommodations being the primary design focus.
Yes, boats are a compromise of design considerations. But I think it is the goal of a NA or designer to minimise the effect of each compromise parameter. And sometimes to make void at times. A good example of this is hull flare. Hull flare creates accomodation space with minimum effect on performance. Cheers
So, as a follow up question, could you ask him how he manages the balance between the variables to create a Performance Cruiser? There are true performance boats (pre-foiling racing cats), there are cruising cats (Leopard/FP/etc), and there is this wide range in the middle called performance-cruisers. Is it all decided by the hull design, or can you take a perf cat and make it a perf cruiser? My guess is it is designed in, and you work within the design parameters (weight loading/balancing) to maintain that perf part of the perf/cruiser. Great series - looking forward to the rest of it!
One of my favorite TT videos so far. Very, very informative. I, like you, want a performance cat, but what Antoine might also be saying is that if you buy a performance cat, and you try to load it the way you would a monohull, you will seriously decrease performance AND comfort, create more slamming, and maybe even hurt stability. In that case, someone who is buying a catamaran mainly as a coastal live-aboard to mainly sit at anchor/moored/tied to a dock with short island hops, might actually want one that is less suited to performance and more tolerant of heavier loads, which might mean a lower hull volume/length number, lower coefficient, etc.? What a journey we're all on here. Knowledge = enlightenment. Thank you Nick.
Technical Tuesday!! WOW WAY more info than I thought I needed to know! Thanks Nick, you just made it harder for me to choose a catamaran now LOL !! Fair winds and following seas Ruby Rose!
Brilliant. I've only ever listened to one other presentation from a marine architect... It fascinates me... Odd really, they do understand what goes on. I'm looking forward to the numbers of the advantages of dagger boards over keels. There is so many myths about both, that a design expert can clarify so much...
Would like to understand performance issues regarding a "plumb bow" and the alternatives. Also big ships have a bulbous bow and pleasure sailing vessels don't. Why not? If it makes a difference on a big ship!
This kind of information seems to be difficult to come across. Thanks for covering it. I wonder about these things all of the time. It's nice to be a little more knowledgeable in the subject.
Thank you very much, Nick! Quite informative and educational! I can honestly say that you were busy while in quarantine/isolation (and while waiting for Terysa to return from australia)...
Thanks...great video explaining some of the concepts. Learned some good information and it caused me to think more about our hull design. What about the balanced load of the contents.... Like the balance in a plane? What are the effects for instance if the weight is unbalanced and you drag your stern or plow your bow? Is part of the performance also a well balanced boat? Port and starboard, bow and stern. Are there optimal balanced loads.... Also will you be selling Ruby Rose merchandise with the wording..."I like your Prismatic Coefficient."
This is great .. thanks so much ! (Don’t take me wrong, but I would like to hear more from the naval architect itself, probably was the way of editing but it looks like Nick is always interrupting the explanation) but this totally great and I’m with you Nick, I prefer to listen to this characteristics rather the color of the galley or sofas... cheers 🍻
This is exactly how I felt. Love you Nick but it felt like you were talking over him a lot and I would have appreciated his longer answers. Also a few times I think you got the explanation around the wrong way and didn’t give him a chance to confirm. Could have been language or editing but both those things are controllable. Still precious info, thanks!
Absolutely #OfTheEpic work once again Nick. You are completely filling or think bank to its brim. Much appreciated. I wish there was a way that somehow we could combine this with all of the other catamaran footage you have and come out with a finished product that is the brainchild/catalyst of everyone’s buyers guide to catamarans and cruiser life there in.
Hi Nick, thanks for the great video, I learned a lot! I think your slenderness ratio is upside down, it should be length / cube root of displaced volume. It seems that a catamaran should only use half the displaced volume since there are two hulls. In this case, assuming 25% over the published light displacement, I get 7.3 for the Seawind 1370, 8.4 for the Outremer 45, and 6.4 for a Lagoon 450S. I wonder how much difference this makes in the real world. Unfortunately, we won't be test sailing the 1370 any time soon.
Catamarans are outselling monohulls 10 to 1 for cruising. Cruising is when you don't need to be somewhere at a specific time, and want space and comfort... The catamarans are ideal for that, heavy or not, it doesn't really matter.
Really appreciate this video, as it is a rare day you get to hear from a naval architect. Thank you, Ruby Rose Team! As an aside, have you heard of whether a closed cell foam core is preferable to balsa core? I thought it was (if for no other reason than things shouldn't degrade as easily) but so many are building with balsa, I'm beginning to wonder?
I assume this was recorded some time ago, so my question is probably going to go unanswered, but I want to know what the benefit of assymetric hull design is. A good example is the Outremer that SLV are on. From top down, there is a pronounced opposing camber similar to a pair of aircraft wings. This should create a low pressure area between the hulls with a corresponding increase in water speed. As a byproduct of this, one would assume the hulls are then in compression which I suppose is OK???
I asked the builder of my Whitehaven 11.7 (designed Mark Pescott) what the Prismatic Coefficient was and he informed me that he could tell me but then he'd have to shoot me! (I never did find out what it was). This was a boat that had hull length/beam ratio of around 12.7 (displacement of 4 tonne) and was capable of outsailing most other cats both upwind and downwind.
Good show (using this term deliberately ) but....I think Nick in good faith is "playing talkshow host rushing slow guest. The title should be "slow Frenchman and fast Englishman on boats" 😀 .....Great graphics ! Waiting for next TT Show
More like a person who is used to being on camera and another who is not (and also not speaking in their native language)... no idea what their nationality has to do with it.
SpinDreams well said, thank you. It is terribly difficult to explain technical science in a foreign language lacking the highly specific vocabulary and having to this on camera! I speak 3 languages and I have thought flight students in all three languages in my past, I know very well about the challenges involved.
Great information! Thanks for sharing! Will the subject of what the sailors call "hobby horsing" be discussed? It seems worse on the shorter lighter catamarans.
2 ปีที่แล้ว
Repetitive pitching is mostly caused by narrow sterns such as in Wharram cats. It is also wise to separate the LCB and the LCF when designing catamarans, to reduce pitching.
Hi Nick, good video and information. Please can you consider creating and leaving a record behind that can be downloaded, of this and the other key facts, that you are indicating will come in the next video's, or do so at the end as a "Summary of things to consider cheat sheet"? That would be super useful . Kind regards Gavin
Fascinating information. My question why can we not put a underwater wing on the hulls to create lift out the water? I can do it with my serf board. Surly being able to even a just the angle of attack of this wing with electric mothers would give optimum displacement to wetted serf ace for a specific speed for a cat? I have never seen it on a carousing cat...why not?
@ I agree cats hare very heavy, and displacement is great. So I am not talking about lifting the cat out the water on its fails like a racing cat. but surly putting fails on and getting the cat to lift up say 6in or 12in above its original waterline is a good thing. Would go faster as less drags? The mechanics would be simple and the electronics needed to trim the fail would also be simple coding with pressure sensors and speed detectors. I know live aboard forgo luxury items like washing machines and dryers and a load more clunky items, but adding fails would be like eating the boat of such equipment and running with an empty cat. I know I must be missing something as no one has done it, what am I not understanding?
Awesome and informative video . Loved it answered a lot of things I did not know but wondered about . cheers to a great video . From Steve Stott in Sutherlin Oregon U.S.A.
I would be interested in center of gravity, both vertically and horizontally. For instance, Could you extend the interior bridge deck forward? How do the catamarans with high booms and lounge areas perform? Also, the design of the transom of mono-hulls has shifted in the last few years to retractable swim platforms; will catamarans ever incorporate that design?
@ No need for retractable swim platforms? Why not? All the monohulls are doing it. Makes cockpit more enclosed (safer) and you get more space. Win-win. The new HH 44 has incorporated it and I'm excited by that
As a boat designer and builder, I don't agree with the naval architect. You can have long slender hulls for catamarans. The issue with cats and multihulls is all about payload / displacement / bridge deck. I believe design to sea state 3 as a rule of thumb. It just becomes less practical. We are talking displacement, the higher the slenderness ratio the better can go to 10 or even 12. Do not confuse foiling with these just yet. That is a whole other HUGE subject and not related to slenderness (I specifically focus on foiling boats and am not interested in displacement, semi displacement, or planing hulls, but need to understand the fundamentals of these first). Foiling boats are in its infancy. One issue to discuss is fouling potential - and design has a part to play (fewer sharp angles!) Generally though, as a starting video on design, to focus on hull is crucial so slenderness ratio and Prismatic coefficients is a great place to start. Well done! Rocker. There is also a aft rocker for both planing and displacement hulls - which affects trim angle through speed variances and hull resistance. Then look at transom design as well.
Great stuff Nick, I always learn something valuable from these talks. Thanks, very eye opening, cant wait until the next boat show...lol...vocabulary quizzes.....hahahaha
Simple: Performance==Start with the hull+rig and fit the interior inside Cruising==Start with the interior and wrap the hull around it with big engines and a smaller rig. More seriously, its interesting how the priorities of hull design change Mono vs Cat. You spend a lot of time on a monohull looking at the righting moment and how that affects the shape (and prismatic coefficient) of the hull, obviously that is not thought of for a cat, These guys are concentrating on hull drag & whetted area, I would have thought a lot more thought would go in to the leverage that the rig can exert before you start lifting a hull and how to compensate for slip. Aerodynamically you often don't worry about the 'whetted' area, it's all about the frontal shape/size. I suppose water creates more drag through contact? So the balance has to be taken between LAW for top speed and drag. Something else to remember is that big heavy boats move more gently = less seasickness for the crew :)
For one who likes details, this is perfect. I hope that you can put together a CliffsNotes summary of the key elements from each episode at the end of the series. Thank you Nick.
I watched and enjoyed the whole thing, which must only mean one thing. I'm turning into my engineer father! (Thanks for keeping it conceptual, and the actual math as minimal as possible. Math is usually were my brain tunes out.)
It’d be brilliant if you could do a video about optimal loading for each length Seawind - trying to decide if an 1160 will realistically meet my husband and I’s needs for about 4-5 years of cruising from the Caribbean to Australia.
It's been done already by many in 1160's already, but owning a 1260 I'd recommend the bigger boat. For 2 people it's a wonderful sized boat, performs well and is easy to manage.
Sailing SV No Regrets We’d love to buy a 1260 but our budget precludes new and there aren’t any (to my knowledge) on the used market in that part of the world. Though I’m definitely going to have a look at your channel now if you sail a 1260 - it’s so hard to find you tubers who sail seawinds (though with ruby rose 2 it may get more popular)
2 ปีที่แล้ว
Pretty much the minimum for an ocean voyaging catamaran for two, I'd say.
Are catamarans stronger in collitions? It is may impresion that if you hit a reef a catamaran is more prone to break apart. They seem more fragil with thinner hulls.
Two Comments 1) Love the intro. I was waiting for Duran Duran to start singing and Nick to start dancing in parachute pants! 2) What a great job working with an engineer that is immersed in the complexities of physics, and simplifying the concepts. As an engineer I run into folks everyday that do not appreciate your questions are NOT simple to answer (in our complex world of design). Nick showed respect for him and his knowledge, while trying to simplify his answers for the audience. Brilliant.
I appreciate a lot the discussion like all the followers intrigued by the technical aspects in the catamarans world...we love being light and fast! (Owning a full foiling A class cat)But is awesome understand the design process of modern Bluewater cruising cat. ciao Terysa!
The whole time I was thinking “this is way more than I need to know!” But I watched to the end anyway and learned a lot. Thanks!
And I'm over hear saying out loud... tell me more, tell me more.
That was informative. But, I was hoping for more info on . 1. How does "rocker" in hull design profile, affect dynamic drag (suction) by vertical or rocking movement of the hull? 2. How does depth of hull affect drag vs displacement? eg. comparing a "V" cross-section having the same displacement as a wide curved but flatter hull cross-secton. Taking into account wetted surface influence 3. How does hull symmetry along the hull centreline affect performance & drag? eg. What if the centerline is not along the centre of the beam but more to the outboard of each hull. Making a wider distance between the centrelines of the two hulls. 4. Are the Port & Starboard hulls both pulled from the same mold?
It would be interesting to see a chart of the slenderness ratio and all the other variables for various 45'ers, lagoon, leopard, seawind, outremer.
I think this comes down to what are your priorities. (Not disputing the analysis, the engineer did a great job of presenting the design/performance theory). Is your priority to sail as quickly as possible? Are you buying a yacht to experience the maximum sailing performance? Are you looking for maximum comfort? Are you looking for minimum draft? If you are looking for performance, are dagger boards a requirement? Etc. This seems to suggest its like Americas Cup and the fastest boat wins. For some this may be accurate, for others its more about the experience of travel and adventure. At one time on early Ruby Rose video’s I remember hearing only a monohull was the preferred sailing vessel. We all watch several sailing channels and obviously the journey is accomplished in MANY different ways. They all seem to achieve their individual objective. I have two cars. One is a GMC Suburban and the other is 911 Porsche. Both will allow be to drive from California to New York however, (and as with everything) there will be tradeoffs. For me my goal is to travel and share an adventure of a lifetime and much less about the design of the yacht. It seems to me The Wynns, UMA, SLV, Delos, O’Kelly’s etc. are all out sailing and achieving their dreams. For me this is the most important criteria.
dagger boards dramatically reduce lee drift.
your sliding sideways without danger boards, and then your course "made good" suffers....point a to point b , what is performance?.....but you honestly don't need dagger boards on a Hobbie 16, because it has a low prismatic coefficient .... so big cruiser cats need dagger boards, where only light beach cats don't.
mono hull keel boats are the most sea worthy ... you don't want to flip a cat ... I guess some of the big heavy cats won't, but that goes back to making the hull lift work for the design ... different cats are designed different for the reasons that they where designed to be what they are .... so if your not a designer, just pick that works for you.
Several years ago I read a book from the 1890's on steam locomotive design and was quite surprised at how much the engineering was based on ratios. Ex. If a part for a certain function needs to be X inches long then it needs to be at least X/12 inches thick. These ratios were derived from what worked in the field and what didn't work rather than from material science and complex maths. Although we now have computers which can perform hydrodynamic calculations in fractions of a second it is interesting to me that we still use ratios when talking about the properties of a boat.
As an Ocean/Naval Engineering student, this is a fantastic exchange of information within the industry. I'd consider myself a customer more concerned with technical aspects rather than the lush and plush stuffed in.
To be straight up, I was worried about getting something less than this, dare I say it im looking forward to it now. Congrats on the new boat, sure your looking forward to it. I remember saying no rush on announcing it as long as you went into all the technical details like you said you were going to. Now you have set the bar high, keeping your word, I like it. You have me looking forward to the rest of this series. Thankyou, in depth technical stuff, if you can do this on everything its bloody awesome. Everyone else does drooling over double sinks and different fabrics and bar areas. This is what I am after myself.
Thankyou Terysa for putting up with him while he delivers this content :P.
I enjoyed the interview but the click bait pic was unnecessary.
Please keep banging on about this stuff!! And a hearty congratulations for finding the yacht for your needs!
I'm a year into research for finding a catamaran for a currently non-sailing couple retiring in a few years time. Finding opinions like 'performance cruising catamaran' and 'usable living space' is easy. But, finding any detailed facts about the science behind this is very difficult.
With very little digging, I can easily know almost all of the dimensions and performance specifications regarding my laptop computer and all of its internal components. And all that info for a small machine that costs only a few thousand dollars!
But, it seems catamaran manufacturers expect us to spend hundreds of thousands of dollars, if not millions, on the vessels they produce, while telling us very little about what actually makes them tick.
I get the feeling they hope to sell us on the romance of the adventure without wanting us to really know what the vessel can and cannot do. With all machines, I am very, very interested in what they cannot do. That knowledge is what allows us to make decisions that keep us safely in the 'can do' zone.
And when buying used, there seems to be even less information available.
So please do keep banging on about this stuff!
Always liked your show. I think there was a typo though. Slenderness ratio is LWL/(HVol)^1/3, the higher the faster, not the other way around. Nowadays mostly the weight+Length+sails determines boat performance. I liked seawind 1260, but the cabin ceiling too low to be comfort. Seems like Seawind 1370 improved. Looking forward to more info on pricing etc.
Yep. There's a typo in that Slenderness Ratio slide at 7:58 .
The slde gave the formula for Displacement to Length Ratio instead.
There is more than just that one typo which makes it hard to watch as an engineer, but nice effort for braking down the engineering side of things!
for some reason I can seem to figure out what prismatic coefficient is and how it affects performance/comfort. they showed a chart but then went on to the next aspect affecting hull performance/comfort.
that being said, I've seen vids of people sailing cats and complaining that the waves "slap" the hulls or the bridge deck and now I understand why. they probably had it overloaded or design was so that the bow waves were crossing into the bridge deck and or hitting the opposite hull. (no idea what cat it was) very informative and interesting. Thank you.
The way I design hulls is to choose a fish that encapsulates the boats personality, the bottom half of that fish is now your hull design below the waterline. :)
LOVE the more technical information. It's something that seems really lacking on the net in any real organized way. Everyone just says "go read The Principles of Yacht Design" which I plan on, but it would be nice if there was an organized repository of this knowledge for those of us who learn better that way than reading whole books of dry information.
Slenderness ratio = Length / Hull Volume. The formula at 8:00 is the DLR (Displacement Length Ratio), which is inversely proportional to the Slenderness ratio. Also the SR is in SI units, the DLR in Imperial units. Since he is talking about actual numbers this is relevant.
Saw this too
These statistics are for the under water portion of hulls. Very little, if any, of a cruising sailboat interior is under water. Waterline beam plus flam determines the interior more than any technical statistic.
Interesting info Nick and it's good top know these things thanks. But will the Prismatic Coefficient really be a factor to discuss for anyone buying a family cruiser, It's a bit slower but we can shower, keep the beer and wine chilled and will get less wet would be the selling point I think. I'd loved to know how they work out the position to place the mast for optimal performance, who decides that it goes further aft or toward the bow for better upwind or down wind sailing. Hopefully you will have that come up in one of your videos.
This is my new Favorite Playlist from Ruby Rose. So many things I am thinking about but just dont seem to be talked about in an approachable fashion. Looking forward to more.
Ah thanks mate
Very good wish I had this info in 89 when I started building my Simpson 12m I would have gone on a diet! Cruised it for 20 years so I must have done something right
Interesting. One shape to consider is hull asymmetry. When viewed from above, a Hobie 16's hull has an airfoil shape: the hull is flat on the outside but curved on the inside. The idea is that it co.pensates for lack of a centerboard: it generates lift for windward performance and reduces leeward drift by presenting a flat surface to the water on the outboard hull. Do modern cruising cats do this?
Nope. Too inefficient
Yes, my new hull design does. It is an improvement on the Hobie design hull. I have tested many 5m prototype hulls and compared to conventional modern dagger board hulls, the results show advantages which are; Superior lateral resistance at all speeds.
High and low speed efficiency without foils.
Excellent sea keeping capabilities. Cheers
Nice work on this video! I was told this series is worth a look and it sure is.
I believe style on a lot of new performance cruisers is still being put before cruising function quite a bit.
Immersed transoms is a great example of racing style looking cool but not functional for cruising.
The wider shorter sterns with immersed transoms only offer more performance once at high speed. They are slower in light air and for performance cruising light air performance is actually more important than a few % more at the top end when your likely slowing down anyway.
If you have anti foul pain on your transom you have wet heels...
Mick
Helo miss, i am a part of an undergraduate student team of Naval Architecture, who is participating in Ferry design compettition , we are designing a catamaran and we require the range of coefficients best for catamaran for e.g Cb ,Cp LBr e.t.c. so we request you to help us in any way you can for that. Thanks a lot.
My own view is that if one is after a performance catamaran stick with something over fifty feet, otherwise it's too much of a battle between narrow hulls and comfort.
I’m not currently not a Blow-Boater but this discussion was fascinating for me. Cat’s have become more and more popular on the Power Boat scene and I am currently thinking about “next” for us and whether to go cat or Knot... (with focus on comfort versus performance) so even for a Motor Head this was an exceptional vid... looking forward to the rest of this discussion!
That makes so much sense now, in fact it`s why I binned my first missus all those years ago!
Over time, her slenderness ratio decreased to the point it dramatically reduced performance and as her wetted surface area increased it had a negative impact on speed, comfort etc and I had to have her bottom scraped more often.
Seriously, thanks Nick, I did enjoy this first foray into the design process and look forward to more of the same ,
cheers easy.
🤣🤣🤣🤣🤣🤣🤣🤣 FFS Mate!
Quality Bert lol
That was informative. We never hear anything about hull design, if you want to know you have to go looking. Other important factors that effect slamming are the distance from the bow to where the bridge deck starts and the shape of the leading edge of the bridge deck. Having the hull shape with a flat section in the stern helps reduce hobby horsing. The charter industry has turned cats into max volume to minimum length boats, at the detriment of sailing ability. What is called a performance cat today is really just a well designed cat that should sail well in all conditions. Cats with all lines led to a single helm with 2 winches and a bank of jammers would have been considered suicide 30 years ago, today it's just a cheap option for under powered cats. If you are interested in buying a cat it's best to sail on as many different brands/designs as possible, there is no substitute for experience. Cheers Rustie.
All that good stuff is coming in the next episodes my friend
Lad might not look as if he has started shaving yet, but he knows his stuff! Still not convinced hull shape would influence my future choice of Cat. Key would be not to overload even a slower cruising cat, but price will be the main factor for me, and in the used market you can get a cheaper FP, Lagoon or Leopard that is still a great safe boat that will cross oceans.(steadily not speedily) I could not get the wife to agree to live aboard a performance cat with narrow hulls. If what your research pans out, Seawind seem to be trying to find a sweet spot between cruising & performance. Hope it does not end in the middle doing neither particularly well, but don't think it will, your future Cat looks awesome, with above average cruising & liveaboard comfort and good potential performance. Looking forward to watching your journey & logging all the lessons learnt for mine!
Exactly that mate!
There are a few old salts on here who seem to think that to have any credibility in the sailing world you have to have skin like sandpaper and a beard you can hide a badger in
For customers that will spend big money on a Catamaran, I would think they spend a lot of time going over this type of information.
But I think everyone knows most buyers just go for the boat that has a nice finish and a great sound system. The science behind fluid dynamics regarding lift and resistance in the water is the most important. Thank's for a great look into a small but complex part of Catamaran design.
This information is not usually readily available.
Tony & Susan here, Thank you so much for including us in your detailed discussions with the designer. I am kind of a geek . And am always interested in the details. Susan would love to see the interior design and colors and plates and glasses. Cheers
What you need to know about a boat to make a well-informed buying decision are all the things you can NOT change. So yes, the hull ratios and shapes are way more relevant than the number of fabrics for the saloon, the size of the winches or the controller of the electrical power system (just to name a few).
You could have asked once you have arrived at your final design what is the additional ‘TPI’ (tonnes per inch immersion) if at DWL. To be honest the basic waterline is an academic (although necessary design datum) I would insist that the DWL includes - All tanks including holding tanks at 95% full, specified dinghy and outboard weight, life raft, specified anchor cable and anchor (otherwise they will ‘short chain’ you😉), solar panels and associated control gear and invertors, an allowance for engineering stores (fluids) and spare gear, Weight of passengers- if boat licence for 6 or 8 so be it - with luggage allowance (say 40 kilos each), food and provisions for certified number of passengers for 3 weeks. If the DWL then compromises the key numbers including bridge deck clearance then the NA has to ‘go round the buoy’ and iterate hull form to achieve the objective. Good vid.😀👍⛵️
Half full tanks are usually used in displacement calculation.
@ I was talking about TPI and DWL - not a displacement calculation.
I'd love to pick his brains myself. Great interview choice. I've always wondered what made the great clippers so fast and just what the architects of the day knew and how that knowledge is applied today.
As with any product, they are designed for the customers. If the customers are more technically savvy then the catamaran companies will pay more attention to these details. Videos like this are great for promoting good design.
I am becoming familiar with these ratios and fluid dynamics because of a more humble project. I am trying to design and build an ultra-lightweight (
Great video, love how you get into the tech sides of the boats instead of just the shiny stuff. A discussion on hull performance rating to rig performance would be a great follow up video.
Keep up the great vids!
This really helped me understanding engineering behind the catamarans, as i am a design graduate taking part in a design competition with no idea about boats and how they work, this was very informative !
A pleasure mate. There’s 5 or 6 episodes of theory in this series, and the actual build video drops tomorrow.
Helo sir, i am a part of an undergraduate student team of Naval Architecture, who is participating in Ferry design compettition , we are designing a catamaran and we require the range of coefficients (e.g 0.345-0.5)best for catamaran for e.g Cb ,Cp LBr e.t.c. so we request you to help us in any way you can for that. Thanks a lot.
GREAT show, waiting in anticipation for the next installment of this series, learnt a hell of a lot from this episode, thanks for bringing in the naval architect to explain this in more detail
Boat design simply explained! Nice. I have watched most of your reviews several times each - good detail.. thank you
I enjoyed this immensely, getting a Bali 5.4 (6 cabins ) by Catana, for business. I need volume, that so much performance, plus structural strength is important to me.
Good job Nick. I want to know these calculations to know what to expect from a boat, and to know what I can’t expect from a boat.
Awesome video from all parties here, very informative (and surprisingly fun) and i look forward to the others in this series.
It’s 2:37 HST. I have insomnia . What a joy to find new episode. 👍😀❤️🌴
I'm here because the information is sound.. See ya next video
I think you are growing into becoming a true catamaran design analyst!
I’m like probably the vast majority of your viewers became excited watching this video about your venture into opening the pandora box of hull/boat design science. You are doing an outstanding job in educating us about the various hull design features impacting performance and comfort. Understanding and awareness of the hull features of your boat has also an undeniable positiv impact in managing the boat more safely by knowing the range and limits of its capabilities!
I truly love what you do and the way you go about educating us and most important handing us the tools to understand boat design.
Job very well done! A BIG THANK YOU, keep on going, excited to see what’s coming next!
Thanks for the interesting interview. I couldn't get the slenderness ratio that was written on one of your blackboards to work out. So, after a little research I found this equation which seems to be correct. SR=Lwl/Vol^0.333 ; SI units
Thanks.
co efficient : drag, prismatic. lengtht beam ratio, bridge deck ,clearence slenderness, shape ,rocker, transom wet area, drawing waterline, got it! cheers! i gonna get building!
Great video. A lot of different terms like drag and displacement and such were thrown around a lot without a lot of context on what they actually are and how important they are to the overall performance. I'm less clear what drag is on a hull and how much it effects performance but I can define displacement. Everything knows what it is, but they don't understand why it's so important. If you had a boat sitting in the water and you froze time and removed the boat, the volume of the hole left in the water is the displacement. Multiplied by the weight of water is the weight of the boat. Displacement is important when you start moving because you have to push water out of the way to make a "new" hole in the water. How much effort this takes depends on how much water and how far you need to move it to make the hole per second. This is why cats are faster than mono hulls. If they have the same displacement, the cat has to move the water half the distance to make the hole it needs.
@ You slightly misunderstood me. What I described wasn't just about the volume of water but also the distance you need to move it. Longer narrower hull with the same total displacement will be significantly faster. Split a single hull into multiple while keeping the same volume of displaced water and it will be significantly faster because the water has half the distance it needs to move. While there are other factors, this is by far the overriding factor to start with.
Good start Nick.
Diagrams are pretty iffy - don’t just uncover a picture of a cat and gloss over - it’s not hard to draw them properly. Look over what Hanneke did with James years ago for inspiration. Some of Tennant’s and Shuttleworth’s are good too. It’ll make things much better to voice over the diagram. Also a slenderness of 7 is pretty ridiculous for a cruising boat - that is less than 10tonne displacement for a 15m/50’ cat! Even if - huge if - the manufacturer can have it leave the yard less than 10tonne, there is no way it will stay under once you cruise. So I think the number he’s chosen doesn’t reflect raising reality in any shape or form and that makes me wonder about other points he makes (although there were no other actual numbers which itself is interesting - is the architect for Seawind going to point out that a length to beam of 8-9 is low if their boat has it?)
Actually, thinking further, I suggest a good chat with Rob Denney of Harry proa “fame” will provide a much needed different perspective of experienced practical multihull development. Terysa can find him in WA usually...
You must realize, it is almost guaranteed that the entire series was filmed some time ago. For one, Nick is in the study room of his parent's home, whereas Nick and Terysa have been back onboard Ruby Rose for some time. Knowing anything from watching these two for more than a couple tech episodes, one would discover that Nick is quite particular and thorough with his research. So, many questions will most likely be answered in the series, but most likely will draw more questions one should then venture into their own research and preferences to address. 🤙
Small cruising catamarans usually have a hull L/B of 8 or so. Larger ones will have 8 to 12, depending on the priorities of the designer for the design. 12 is fast, 8 is roomy.
Tech Tuesday ! YES ! Thanks Nick
Thanks Nick, I’m feeling like a geek now :)
Right up my street, I have a slight advantage as I studied stability at south tyne side marine college and found this very interesting. In my opinion I would have dagger boards due to 9 x out of 10 I'm always sailing to windward.
Excellent
I'd check the performance of a seawind first. We sail ours comfortably at 30 degrees AWA with main and jib. They point pretty well for a cat
I've just put the euro lottery on, its £42 million, after watching all of your you tube videos on cats I'll be purchasing one, with that kind of cash I could go OTT on a yacht but any thing over 55ft is a waste for two people in my opinion 🚣♂️🚣♂️🚣♂️🚣♂️🚣♂️
Interesting. But, one important consideration that was addressed but passed over very quickly, is the law of buoyancy or Archimedes principal. Regardless of the ratios that impact performance and lift at speed (i.e. dynamic performance), one has to understand that for any given weight of boat and load, the volumetric displacement of the hull will be the same. Archimedes Principal basically states that the weight of, in this case, a fully loaded boat, will have to displace the volume of water of that same weight. In other words, a cruising boat or a performance boat of the same weight, will have to have the same volume of hull below the waterline (i.e. the volumetric displacement will be equal). That is why, I am assuming that performance boats have to be lighter which is intuitive, but also required, because narrower hull for any given length of boat will have has less volumetric displacement therefore, will only support a lighter fully loaded boat. Therefore hull DISPLACEMENT will always be directly related to the boat weight.
correct, but that's the whole issue, these superficial videos about hull design never really expose the impacts of specific design decisions. They cover generalities and make the viewer believe they understand better. They do not. All they should understand is that is the topic way more complicated than they understand. Engineering is hard. Dunning-Kruger is real.
To carry a specific load (boat + gear + people) It is not the displacement that is important, it is the shape of that displacement and the vast tradeoffs in that shape design...
Ignorance is a curious thing.
What is your point? Displacement can be bare hull, fully loaded, loaded for offshore, loaded for living aboard, loaded with half full tanks, etc.
@ My point was simply that in my experience many people don't know the law of buoyancy - it isn't necessarily common knowledge and it wasn't explicitly explained in the video. So, I was just pointing out that for any given designed displacement or weight of a boat, that in itself, will define the displacement of the hull (or the volume of hull that is below the waterline). So, it you want the hulls to be narrower, then they will have to be longer or conversely if you to the length of hulls to be shorter, than the hulls will have to be wider. In other words, from a design perspective, if someone wants to build a boat that fully loaded is say 20 tons and they also want it to be no more than 45m long, than the choice of how wide the hulls are be will not be much of a choice, as the hulls will have to be as wide as they need to be at 45m long to displace a volume below the water line that equal to 20tons of water. More simply, if someone had a row boat and wanted to know how much weight it could carry, then they could put it on a scale and weigh it and then fill it full of water to the point that water is spilling over the gunnels. Take that total weight and subtract the weight of the boat and the result is how much it can carry before it sinks.
Beautiful the scenery is so beautiful and stunning.Very enjoyable! Reminds me of my trips where I take the good music like the Guns N Roses, Imagine Draongs or the Delta Parole and then enjoy the powerful feeling of the sea. ¡vamos!
"Vertical dynamic lift" Is that also called 'planing'? (Factoid: The Aleuts were planing at about 8 knots and could sustain 10 knots over distance. This was reported by Captain Cook's navigator, probably the best technical source available in the 18th century. Maps they made of New Zealand were used into World War Two).
Loading the boat. I'm a terrible backpacker. Some backpackers walk thousands of mile and their backpacks never exceed 20 lbs. Me 4-5 days 50 lbs. However, I weigh everything, make a spreadsheet, sweat every ounce - otherwise my pack would be 80 lbs. I don't think cruisers get this extreme, but I'll bet a couple of good scales, a spreadsheet and some obsessiveness would shave a lot of excess weight and also point out where it is. Instead of canned goods maybe another freezer might give you more and better vegetables at less weight - just maybe, I have no experience (yet).
Great series. Probably going to save me a lot of money, and a lot of disappointment when I buy a multihull.
my preferred concept...how fast can I make this thing go, comfort be damned! These engineering concepts and detailed analysis, is also applicable to automotive design. I want to know spring rates, alignment specs, tire specs, and all the pedantic details. As an enthusiast, I love this analysis series!
Except that the tyres, suspension and bushes are not just for the driver but for the vehicle. Comfort plays a role in speed, if the ride is harsh it puts a lot of stress on the hull/chassis, which means they need to be stronger, which means more weight. Engineering is fun. Just think of why F1 cars still have suspension.
Prismatic coefficient!!
Ha ! Now I’m off to impress my friends
Thanks Nick looking forward to more
Haha. A pleasure mate
Well done, Nick and guest! Looking forward to the next installment!
Interesting information. Do mfg’s publish the empty weight (leaving the factory) and the useful load? This is done with airplanes.
2 tons is not a lot of weight especially if the boat is not fully outfitted with cruising gear. Generators, dingy (with motor ) water makers, various sails. The list goes on... then there is the Pabst Blue Ribbon too!
Yes, boat designs are quoted in light displacement, which is nearly empty and loaded displacement, which includes full fuel, water, supplies, people, etc. There's also something in between which is often called normal displacement, sort of a typical value. Similar idea to aircraft, for similar reasons.
It is hard to get technical information for retail product boats of any kind.
That was cool. And yes you need dagger boards
Or a centerboard, preferably one that can be raised and lowered.
For performance yes, cruising I'd disagree. When you kiss the bottom with daggerboards you snap stuff off, and potentially bust up your sail drive and rudders. Mini keels protect all that and if done right can still offer some performance. Seawinds 1160 and 1260 models are mini keeled and perform well
F' me, this was brilliant!
Thanks ,you guys have really stepped up your game. Signing up as a Patron.
Ah thanks mate! Happy to see you on Patron and hope to chat on the WhatsApp group
This is an interesting and massively useful subject I am only surprised that someone else has not done so before this.
Cheers mate
Interesting interview, thanks for putting it together.
These concepts are of course interesting, but in the end the most useful tool to assess the performance of a boat are its polars right? They factor in all the aspects including water and air drag, the size of the sails, their interactions, the static and dynamic righting moment (for boats that generate some), the impact of heeling (less relevant for catamarans), the ability to plane,... It's next to impossible to anticipate the resulting performance from considering isolated aspects even if yes, a more narrow hull will typically mean more speed.
This being said, when you watch videos of the recent Vendee Arctique, it seems clear that performance is just part of the story for passage mating. I would argue that comfort is also key and that is probably even harder to assess from isolated boat characteristics than performance. Speaking about monohulls, one rather unintuitive thing I learned recently is that boats with lifting centerboards are often more comfortable at anchor (less motion) compared to those with lifting keels, because the centerboarders are designed to have balast independantly of the weight of the keel, so they remain stable even with the centerboard up. This to say that considering only the performance value of a keel would result in overlooking this essential aspect of comfort at anchor.
Sailing catamarans don't have ballast. It is widely agreed that weight is the biggest determiner of sailing catamaran speed.
great discussion, I would however suggest you have (like any of us would after making a boat buying decision) a bias towards a certain design which is steering the discussion. The several times said "there are no bad boat designs just different intentions" (paraphrased a bit) should be talked about much further because it is all compromise and we are just looking for our ideal compromise (not just yours). Objectivity would show for each feature that might compromise speed could add comfort so in a so forth through all of your excellent talking points. It is also important to frame this discussion with the scale of actual differences in sailing performance. My point being that is you watch the ARC races (for example) there are plenty of well skippered "condomarans" finishing well up the order every single year. Yes it's won by a Gunboat but there are plenty of Lagoons and FP's in front of and intermingled with the "performance" cats. That is because other factors have a bigger bearing on performance than simply hull design. It would be cool to talk about these real world influences at some point with objectivity and holistically look at the realities of getting from point A to point B (circumnavigation: Point A to Point A!) with the perfect blend of speed AND comfort for different types of sailers (and sometimes queasy reluctant crew). Your Naval Architect wants to say it but you won't let him because you keep steering the conversation towards performance being the answer
Boats should be designed for their intended use, but bad designs do exist, I'm afraid. Alas, the average boat is designed to please wives who are thinking of short family vacations, with accommodations being the primary design focus.
Yes, boats are a compromise of design considerations. But I think it is the goal of a NA or designer to minimise the effect of each compromise parameter. And sometimes to make void at times. A good example of this is hull flare. Hull flare creates accomodation space with minimum effect on performance. Cheers
So, as a follow up question, could you ask him how he manages the balance between the variables to create a Performance Cruiser? There are true performance boats (pre-foiling racing cats), there are cruising cats (Leopard/FP/etc), and there is this wide range in the middle called performance-cruisers. Is it all decided by the hull design, or can you take a perf cat and make it a perf cruiser? My guess is it is designed in, and you work within the design parameters (weight loading/balancing) to maintain that perf part of the perf/cruiser.
Great series - looking forward to the rest of it!
Great information in understanding catamaran design for the uninformed. Really helpful. Thanks
Glad it was helpful!
One of my favorite TT videos so far. Very, very informative. I, like you, want a performance cat, but what Antoine might also be saying is that if you buy a performance cat, and you try to load it the way you would a monohull, you will seriously decrease performance AND comfort, create more slamming, and maybe even hurt stability. In that case, someone who is buying a catamaran mainly as a coastal live-aboard to mainly sit at anchor/moored/tied to a dock with short island hops, might actually want one that is less suited to performance and more tolerant of heavier loads, which might mean a lower hull volume/length number, lower coefficient, etc.? What a journey we're all on here. Knowledge = enlightenment. Thank you Nick.
A pleasure mate
Please continue to make these technical videos. I loved it.
Technical Tuesday!! WOW WAY more info than I thought I needed to know! Thanks Nick, you just made it harder for me to choose a catamaran now LOL !! Fair winds and following seas Ruby Rose!
Brilliant. I've only ever listened to one other presentation from a marine architect... It fascinates me... Odd really, they do understand what goes on. I'm looking forward to the numbers of the advantages of dagger boards over keels. There is so many myths about both, that a design expert can clarify so much...
Don't forget the center boards with the "break away" design like McConaghy.
Would like to understand performance issues regarding a "plumb bow" and the alternatives. Also big ships have a bulbous bow and pleasure sailing vessels don't. Why not? If it makes a difference on a big ship!
This kind of information seems to be difficult to come across. Thanks for covering it. I wonder about these things all of the time. It's nice to be a little more knowledgeable in the subject.
Thank you very much, Nick! Quite informative and educational! I can honestly say that you were busy while in quarantine/isolation (and while waiting for Terysa to return from australia)...
Thanks...great video explaining some of the concepts. Learned some good information and it caused me to think more about our hull design. What about the balanced load of the contents.... Like the balance in a plane? What are the effects for instance if the weight is unbalanced and you drag your stern or plow your bow? Is part of the performance also a well balanced boat? Port and starboard, bow and stern. Are there optimal balanced loads....
Also will you be selling Ruby Rose merchandise with the wording..."I like your Prismatic Coefficient."
This is great .. thanks so much ! (Don’t take me wrong, but I would like to hear more from the naval architect itself, probably was the way of editing but it looks like Nick is always interrupting the explanation) but this totally great and I’m with you Nick, I prefer to listen to this characteristics rather the color of the galley or sofas... cheers 🍻
This is exactly how I felt. Love you Nick but it felt like you were talking over him a lot and I would have appreciated his longer answers. Also a few times I think you got the explanation around the wrong way and didn’t give him a chance to confirm. Could have been language or editing but both those things are controllable. Still precious info, thanks!
Absolutely #OfTheEpic work once again Nick. You are completely filling or think bank to its brim. Much appreciated. I wish there was a way that somehow we could combine this with all of the other catamaran footage you have and come out with a finished product that is the brainchild/catalyst of everyone’s buyers guide to catamarans and cruiser life there in.
Hi Nick, thanks for the great video, I learned a lot! I think your slenderness ratio is upside down, it should be length / cube root of displaced volume. It seems that a catamaran should only use half the displaced volume since there are two hulls. In this case, assuming 25% over the published light displacement, I get 7.3 for the Seawind 1370, 8.4 for the Outremer 45, and 6.4 for a Lagoon 450S. I wonder how much difference this makes in the real world. Unfortunately, we won't be test sailing the 1370 any time soon.
Just subscribed. Good topic, looking forward to more of the physics in design.
Catamarans are outselling monohulls 10 to 1 for cruising. Cruising is when you don't need to be somewhere at a specific time, and want space and comfort... The catamarans are ideal for that, heavy or not, it doesn't really matter.
This is quality content I'm looking forward to this entire series.
I love this series thank you so much!
thanks for focusing on the details
Really appreciate this video, as it is a rare day you get to hear from a naval architect. Thank you, Ruby Rose Team! As an aside, have you heard of whether a closed cell foam core is preferable to balsa core? I thought it was (if for no other reason than things shouldn't degrade as easily) but so many are building with balsa, I'm beginning to wonder?
That my friend is covered in extreme detail in a later episode.
I assume this was recorded some time ago, so my question is probably going to go unanswered, but I want to know what the benefit of assymetric hull design is. A good example is the Outremer that SLV are on. From top down, there is a pronounced opposing camber similar to a pair of aircraft wings. This should create a low pressure area between the hulls with a corresponding increase in water speed. As a byproduct of this, one would assume the hulls are then in compression which I suppose is OK???
Thank you, very valuable information, waiting for the rest.
I asked the builder of my Whitehaven 11.7 (designed Mark Pescott) what the Prismatic Coefficient was and he informed me that he could tell me but then he'd have to shoot me! (I never did find out what it was). This was a boat that had hull length/beam ratio of around 12.7 (displacement of 4 tonne) and was capable of outsailing most other cats both upwind and downwind.
Good show (using this term deliberately ) but....I think Nick in good faith is "playing talkshow host rushing slow guest. The title should be "slow Frenchman and fast Englishman on boats" 😀 .....Great graphics ! Waiting for next TT Show
More like a person who is used to being on camera and another who is not (and also not speaking in their native language)... no idea what their nationality has to do with it.
To be fair to the Frenchman, his English is infinitely better than my French. I thought he did great.
SpinDreams well said, thank you. It is terribly difficult to explain technical science in a foreign language lacking the highly specific vocabulary and having to this on camera! I speak 3 languages and I have thought flight students in all three languages in my past, I know very well about the challenges involved.
@@olliewillson9803 Are you telling me? or just expressing your opinion, I was the one who pointed out that the OPs comment was somewhat racist.
Well, when we were racing cats we only thought about the drag of one of the hulls!
Thanks guys. Very informative. I’d love to have some statistics of the various Seawind models over time. Any chance of getting those?
Great information! Thanks for sharing! Will the subject of what the sailors call "hobby horsing" be discussed? It seems worse on the shorter lighter catamarans.
Repetitive pitching is mostly caused by narrow sterns such as in Wharram cats. It is also wise to separate the LCB and the LCF when designing catamarans, to reduce pitching.
Hi Nick, good video and information. Please can you consider creating and leaving a record behind that can be downloaded, of this and the other key facts, that you are indicating will come in the next video's, or do so at the end as a "Summary of things to consider cheat sheet"? That would be super useful . Kind regards Gavin
Fascinating information. My question why can we not put a underwater wing on the hulls to create lift out the water? I can do it with my serf board. Surly being able to even a just the angle of attack of this wing with electric mothers would give optimum displacement to wetted serf ace for a specific speed for a cat? I have never seen it on a carousing cat...why not?
@ I agree cats hare very heavy, and displacement is great. So I am not talking about lifting the cat out the water on its fails like a racing cat. but surly putting fails on and getting the cat to lift up say 6in or 12in above its original waterline is a good thing. Would go faster as less drags? The mechanics would be simple and the electronics needed to trim the fail would also be simple coding with pressure sensors and speed detectors. I know live aboard forgo luxury items like washing machines and dryers and a load more clunky items, but adding fails would be like eating the boat of such equipment and running with an empty cat. I know I must be missing something as no one has done it, what am I not understanding?
Awesome and informative video . Loved it answered a lot of things I did not know but wondered about . cheers to a great video . From Steve Stott in Sutherlin Oregon U.S.A.
I would be interested in center of gravity, both vertically and horizontally. For instance, Could you extend the interior bridge deck forward? How do the catamarans with high booms and lounge areas perform? Also, the design of the transom of mono-hulls has shifted in the last few years to retractable swim platforms; will catamarans ever incorporate that design?
@ No need for retractable swim platforms? Why not? All the monohulls are doing it. Makes cockpit more enclosed (safer) and you get more space. Win-win. The new HH 44 has incorporated it and I'm excited by that
As a boat designer and builder, I don't agree with the naval architect. You can have long slender hulls for catamarans. The issue with cats and multihulls is all about payload / displacement / bridge deck. I believe design to sea state 3 as a rule of thumb. It just becomes less practical. We are talking displacement, the higher the slenderness ratio the better can go to 10 or even 12. Do not confuse foiling with these just yet. That is a whole other HUGE subject and not related to slenderness (I specifically focus on foiling boats and am not interested in displacement, semi displacement, or planing hulls, but need to understand the fundamentals of these first). Foiling boats are in its infancy. One issue to discuss is fouling potential - and design has a part to play (fewer sharp angles!) Generally though, as a starting video on design, to focus on hull is crucial so slenderness ratio and Prismatic coefficients is a great place to start. Well done!
Rocker. There is also a aft rocker for both planing and displacement hulls - which affects trim angle through speed variances and hull resistance. Then look at transom design as well.
Great stuff Nick, I always learn something valuable from these talks. Thanks, very eye opening, cant wait until the next boat show...lol...vocabulary quizzes.....hahahaha
Simple:
Performance==Start with the hull+rig and fit the interior inside
Cruising==Start with the interior and wrap the hull around it with big engines and a smaller rig.
More seriously, its interesting how the priorities of hull design change Mono vs Cat. You spend a lot of time on a monohull looking at the righting moment and how that affects the shape (and prismatic coefficient) of the hull, obviously that is not thought of for a cat, These guys are concentrating on hull drag & whetted area, I would have thought a lot more thought would go in to the leverage that the rig can exert before you start lifting a hull and how to compensate for slip.
Aerodynamically you often don't worry about the 'whetted' area, it's all about the frontal shape/size. I suppose water creates more drag through contact? So the balance has to be taken between LAW for top speed and drag.
Something else to remember is that big heavy boats move more gently = less seasickness for the crew :)
For one who likes details, this is perfect. I hope that you can put together a CliffsNotes summary of the key elements from each episode at the end of the series. Thank you Nick.
I would love to know more about bridgedeck clearance, how low can it be. And on construction about strip planked wooden hulls!
I watched and enjoyed the whole thing, which must only mean one thing. I'm turning into my engineer father!
(Thanks for keeping it conceptual, and the actual math as minimal as possible. Math is usually were my brain tunes out.)
Geek Tuesday, but a great overview of the principles
It’d be brilliant if you could do a video about optimal loading for each length Seawind - trying to decide if an 1160 will realistically meet my husband and I’s needs for about 4-5 years of cruising from the Caribbean to Australia.
I think Seawind have those loading statistics. Did you ask Shane?
It's been done already by many in 1160's already, but owning a 1260 I'd recommend the bigger boat. For 2 people it's a wonderful sized boat, performs well and is easy to manage.
Sailing Yacht Ruby Rose no I didn’t but I will now that I know who to ask for sure
Sailing SV No Regrets We’d love to buy a 1260 but our budget precludes new and there aren’t any (to my knowledge) on the used market in that part of the world. Though I’m definitely going to have a look at your channel now if you sail a 1260 - it’s so hard to find you tubers who sail seawinds (though with ruby rose 2 it may get more popular)
Pretty much the minimum for an ocean voyaging catamaran for two, I'd say.
at last away from the bs and down to the needed detail well done nick
Cheers mate.
Are catamarans stronger in collitions? It is may impresion that if you hit a reef a catamaran is more prone to break apart. They seem more fragil with thinner hulls.
Antoin didn't make it understandable, you did. Great questions! Great video!
Two Comments
1) Love the intro. I was waiting for Duran Duran to start singing and Nick to start dancing in parachute pants!
2) What a great job working with an engineer that is immersed in the complexities of physics, and simplifying the concepts.
As an engineer I run into folks everyday that do not appreciate your questions are NOT simple to answer (in our complex world of design). Nick showed respect for him and his knowledge, while trying to simplify his answers for the audience. Brilliant.
Thanks mate
I appreciate a lot the discussion like all the followers intrigued by the technical aspects in the catamarans world...we love being light and fast! (Owning a full foiling A class cat)But is awesome understand the design process of modern Bluewater cruising cat. ciao Terysa!