Hi Nick, we just kinda met.... I'm still watching my first video, just paused it, then checked out your channel and I must say I'm happy to meet you. Very in-depth direct info, very well delivered with passion. Well done and I'm excited to learn more. Thank you.
man, thank you so much.. ive been trying to design a waterjet for some time and theres so little information on this subject online, and out of the blue comes this guy and answers every question i had
My father, a boat builder in New Zealand in 1964, accepted Hamilton's, and the world's, first ever jet boat, as a trade-in. He passed it on to Hamilton himself. At the same time he was building a high country deer recovery, flat bottom, 25 footer with two Chrysler Interceptor V8s, with race cams and twin, four barrel, Holly carbs, totalling 800 horsepower. The fastest and most powerful of its day. It could carry a ton across wet gravel, fifty feet, and then into a foot of water.
I was picking my nozzle when my wife handed me a tissue and told me I was being gross . So when you pick your nozzle try to do it in private . DIY tip of the day .
Great video. Basically confirms everything I already know. And how I know is about 12 years ago after years of racing rc cars I had decided to get into boats, but I wanted to custom build my own. Part way into build while researching stern drives I came across jet pumps made by a company called Graupner. Having a huge love for jet engines I was immediately intrigued. I ended up purchasing a 29mm jet pump with reverser for $80-90. It came completely unassembled so I had to put together which sounded easy (YEAH RIGHT!) Was a pain cuz there was only fraction of mm between impeller & side wall. So lining the drive shaft had to be PERFECT or impeller would scrape. Almost didn't think I was gonna pull it off but somehow I did. All I know is in the years since that thing has taught me ALOT about both the physics as well as the design of those amazing things lol. I still have it which I've installed into a "drive-box" that I use to demonstrate to people. It might only be 1 1/2" diameter and about 10" long but when coupled with a 40k rpm brushless motor it will shoot water 40-50 feet. Impressive little thing. All I know is mostly through observing it and the video essentially just confirmed it all.
The first thing that came to my mind took me by surprise: This is way more more rocket science than your average boating. Instead of "biting into the water" prop style you are dealing with a reaction engine. Very intresting
@@shurmurray I'm refering to a reaction engine, like it expells mass at a (hopefully high) velocity as a means to gain direct propulsion. The faster it is thrown out = higher thrust, The heavier the matter it tosses out = higher thrust. A car uses friction to gain propulsion. A water jet (having a snorkle to continue to suck water) would keep accelerating just as well in free air because it is tossing a ton of water per minute out the backside at a considerable speed. A std boat propeller would be using the pressure differential I guess.
@@Paxmax the underlying principle is the same: vehicle pushes off something - either from a chunk of water or a whole planet. Or other way around: the impeller uses pressure difference in pumped water to produce thrust :) There is really not much difference beside external appearance and efficiency.
@@shurmurray Cars(tire friction) and boat/airplane propellers(pressure gradients) do not work in the vaccum of space, reaction engines do. It's kind of an important difference between the means of propulsion. If you have a big bag of water attached to the water jet it would create propulsion in space (if we disregard other circumstancial show stoppers such as a std combustion engine(normally powering the impeller) does not operate in vaccum and the water would tend to violently boil because of the lack of pressure).
@@Paxmax yes - all means of propulsion rely on some spare mass to throw backwards. Jet pushes water (gas, air...), car pushes the whole Earth. They can't move (change velocity) without that reaction mass - car without ground and water jet without water. Attaching tank of water to a water jet to make it work in space - the same way we can attach a patch of a road to a car. Replace gravity with some magnets to ensure wheels are pressed against that patch of Earth - and car going to be able to increase it's forward velocity in space until the chunk of road ends and completely separates flying backwards.
Just today I was designing my waterjet and I had questions, like a light from heaven this video appeared, well in my search results. It's like he knew 4 years ago this day would come, uncanny.
Variable geometry exit nozzle? Maybe not like the variable exit nozzle on a fighter jet, but more like the air intake on the SR71 Blackbird. More suitable for mixed flow pump.
One thing that comes to mind when thinking about this is, "why not have the pipe inlet on the front to reduce drag from water changing direction up into the pipe?" At least, on something other than a fast planing vessel where only the bottom of the hull is in contact with the water. I am guessing the reason is that skin friction inside the pipe would be a much greater effect than the gain (discounting the fact that you also have to slightly enlarge your hull to maintain displacement)?
Excellent point. The trade off of skin friction in the pipe is a challenge to get around. One major concern is that we want the steering force in the aft end to maintain directional control. It becomes much harder with the steering only in the front end.
I use a variable nozzle that actually changes shape long the curve to maintain peak efficiency. I also use a variable inlet. I use a variable impeller as well which adjusts as speed increases. thanks for these videos they helped me come up with some great designs.
Thanks for sharing your video with us, This is great information, I committed with a question on one of your past jet video, it’s almost like this one answered my question, the agency I work for is about to dump about 100k on a new trim setup, after they fail i will show them this video . Cheers
Really informative video, Nick. You always make good stuff. I had one question though. You say that discharging below the waterline is bad because of the higher external pressure. But wouldn't the elevation change increase the stagnation pressure in the water flowing out the nozzle by just as much, thereby canceling that effect out?
Excellent question. I had to think about this one. It's true that the change in static pressure is the same, due to the elevation change. But the dynamic pressure from the waterjet (equivalent pressure from the velocity) is much higher than just the static pressure. To make valuable use of that dynamic pressure, we need free flowing water from the outlet. Otherwise, the viscosity of the surrounding water and the static pressure slow down our outlet flow. It isn't strictly a matter of static pressures. It's also the momentum of moving that much water. We encounter less resistance if there is nothing in the way at the outlet.
What if the stator blades double as the nozzle? The blades stop the rotation of the water and reduce the circumference for thrust. Remember, water doesn't like to be compressed. I had another thought: what if the impeller blades were spun by the outside (still inside the housing, just outside of the blades)? Maybe variable pitch blades too? This might help with the problems that hydroplanes face with the wings being under water.
I learnt a lot with this video, thank you! However, I'm pretty sure all these constraints have been studied thoroughly and engineered solutions have been brought. Being more an "artist" than an engineer, I was wondering if a few things would be mechanically possible/advantageous: - a variable nozzle diameter (a.k.a. "iris door") to adapt the diameter of the nozzle to the speed of the impeller/flow/thrust: would it have some beneficial effect on any parameter? This would be pretty easy to implement with some electronics, but is it even relevant? - floats both side of the nozzle to force it at a mostly constant level from the water line: Would the fold induced in the water path have a strong influence on the efficiency? - a spoon-like cap (like on Pelton turbines) above the nozzle to redirect the outflow mostly horizontally instead of dispersing nearly vertically: would it waste thrust, or the gain would outweight the loss of thrust? - the shape of the impeller: a few years back, Integza made tests on different shapes of impellers and came with a "lily impeller" (there's a ready-to print model on GrabCad). It would certainly make the path much longer, but is there a specific type of impeller to put in a water jet, or anything goes, it depends of the thrust and the engine power? - for the inlet: to reduce turbulence, planes have winglets at the tip of the wings. Would putting fins near the inlets with the goal to drive and rectify the inflow work, or is it pure fantasy? Thank you for sharing your views on this!
That is exactly what I was thinking as well. It seems like some intermediate effect could be had with a simpler design than a fighter aircraft jet nozzle. Perhaps just some moving baffles which reduce the effective nozzle cross section, but do not direct the flow equally in all directions like a fighter aircraft (just balanced on each axis).
Yes, in theory you can change the inlet size to adjust waterjet performance with speed. In practice, I have never seen a commercial waterjet that does this. Too much complexity, and one more control that the captain needs to worry about. There may be some specialized military applications that do this. Military are the only people I can imagine who could afford the development cost of a custom waterjet design.
Do you show somewhere an efficiency comparison between propeller vs. waterjet? the baseline efficiency is always difference between ship speed and speed of accelerated water from the propeller or jet..... I am also not quite sure what efficiency relation you are referring to in the slide shown?
Do they have to be exactly similar in size and shape for it to work, or would a progressive pitch angle work? Since water cant be compressed, they would have to be identical, right?
I want to make a water jet unit for a 19hp engine what diameter should the impeller be? Is there some sort of calculator of how to build it otherwise it will just be a spinny thing in a tube
Thanks for the video. It was very informative. I was thinking of putting 3 x 16mm water jets in a cake tin (to be removed with ease) to screw on the bottom of a surfboard. Gathering from this video it wouldn't work. I want to make a motor to get a 9"7' longboard moving at a reasonable pace to have a bit of fun at the beach with the kids. Any suggestions would be much appreciated. Regards. Mick
I think i would first try a single dc variable speed motor with a prop, maybe a motorcycle battery. If gas, i dunno, a moped engine? I imagine a ktm 50 might be a little peppy on a surfboard
I am designing a surfboard with a water jet pump. I only need it to for short burst of energy. What I am trying to accomplish is a 5-15 second boost to help with catching the wave prior to take off. Where can I find water pumps to buy COTS type. Perhaps 1-2 inch diameter.
So I have a couple of questions: 1. Could the inlet be placed at the front of the boat to utilize the pressure created by the bow wave to facilitate water intake, reducing the distance the water needs to rise before ejecting from the nozzle, and allowing for a more interesting configuration of engines, pumps and nozzles? 2. Is it absolutely vital to have the waterjet at the rear of the boat? For example on a large displacement hull could the nozzles be placed on the sides of the hull above the waterline with buckets to control the flow fore and aft thus making even the largest of ships able to "strafe" without issue. If the waterjet is above the waterline it wouldn't interfere with hydrodynamics. My biggest concern would be bucket wear.
1. this is not a very good idea, you want to have the intake compleatly under water at all times to ensure that do dont have any air in the pump. the intake is formed so the water gets pressed in to the tunnel at speed, so you are using the movement of the boat to your advantage . what is also happening is that you create a flow of water close to the hull and this reduses the friction. In general all waterjet driven boats travel at speeds that are above "the hump". normally +30 kn. 2. Some special appilications do this. normally the "strafe" is a small part of manuvering. you need to have a efficent forward motion to reduce fule cost and get the top speed. if the side motions are important to that degree one could install a bowthruster quite cheap and get similar effect. If you move the jets to the side you get a lot of rotation of the ship. i know installations that use this for manuvering, mailny amphibious vehicles , its simple but not at all efficiant.
@@filipledin6548 Interesting. With regard to point 1 though, what if you're talking about a large displacement hull where it's not above the waterline, the idea being to basically create a low pressure system at the front of the boat equal to the high pressure system creating the bow wave thus creating an even parting of the water down the length of the hull. No bow wave at all essentially. I did the math, the idea is essentially to have a square bow and the area of the bow (in square meters) times the speed of the boat (in meters per second) equals the total volume of water (in cubic meters per second) that needs to be moved from the front of the ship to the back of the ship. Provided the jet is moving roughly that much water there should be no bow wave to overcome. Designing it so that it doesn't suck air, at least in calm water, shouldn't be too difficult I would think, then again this isn't my field.
@@samoldfield5220 I know some about jets, but im no naval architect what so ever. What i described is the general idea why its placed as it is and the logic behind it.
Great explanation :) So now i have a question.. Im building an RC model of a yacht Project Infinty by Dorries yachts and because me being me this means that i'm not building a 1m model but a model that will be 3m long (1:30 scale) and i would like it to be powerfull enough to pull a skier on water (total weight of the model est. to be arround 120-130kg ) So how can i calculate how big impeller do i need and how powerfull engine to run it? (Im going to do it with dual jet powered by an electric motor I'd be very gratefull for any sort of information. Thanks
think of an impeller as a pop can. calculate the volume, then multiply by blade number. figure the wqeight of the water, then calcculate the speed of the water at the Nozzle coming out. for example. pop can weighs 1LBS(just an example) thats the volume of your impeller times 3 for each blade, so 3 lbs. Depth of impeller is the water speeds plug in, if you have an impeller that is pitched(of deep/height of a cylinder) for one rotation its 3 pounds moving the hieght of your cylinder, then RPM is the speed at which it moves. you have to calculate how much weight is pushed and at what speed in order to get your total force. sorry its been a minute since i had to calculate it so the text is choppy haha! hope that helps for an idea of how to proceed with research!
Jetboards generally use a nozzle including stator vanes to increase waterflow velocity and efficiency. Commercial boards use boosterjet setup; the rider is controlling the board by shifting his/her weight.
What about the efficiency of a propeller as a semi jet propulsion unit?? A propeller style jet pump without the nozzle. I am curious. Can it be tucked under the watercraft like a jet pump and be efficient??? Could this be your next content??
Strictly speaking, no. A waterjet is specifically designed for surface propulsion. There is a similar device used for underwater propulsion called a pump jet. These are popular on military submarines.
I'm a novice here. Trying to learn as much as I can from a physical standpoint. So I may ask silly questions. Every time I think of jet propulsion I think of how it compares to sterndrives, or propeller drive if you will, and why the loss in efficiency compared to the sterndrive. On outboard motors I see for example 60/40 horsepower. So 60 engine horsepower but only 40 horsepower at the impeller? Or is this horsepower being measured by a different means, like thrust? Because thrust can be converted to horsepower in the case of turbine engines so I assume that might also apply to waterjets as well. I can't comprehend how 20 horsepower would be lost from the crankshaft to the impeller since it's a direct connection. My only guess is 20 horsepower is consumed moving water through a narrow passageway under high pressure, and what we get in return is 40 horsepower worth of thrust, if that makes sense. Whereas as the impeller moves a "low volume" of water under high pressure and velocity, the propeller moves a much larger volume of water at lower velocity and "no pressure", so to speak. It's simply under the water it's only job is to move the water rearward the vessel......unless you're going in reverse. First question, is my statement correct, at least partly? Second, theoretically, could a waterjet be designed almost opposite of most current waterjets today where it moves a larger volume of water at a lower velocity and pressure (to a point) like the propeller drive, and be closer to the efficiency of the propeller drive? Yes, I'm aware of the concern about cavitation. For now let us pretend it isn't a factor. The point of all this is I do like jet propulsion but I HATE the loss of efficiency and speed compared to a propeller drive. I would love nothing more than to see the efficiency deficit addressed but until I do, I won't tolerate the loss in speed just so I can operate in shallow water.
You are mostly correct. 1.) yes, the loss in power is referring to the effective power delivered from the impeller. There is a tiny loss due to friction in the impeller shaft (2%-4%), but the major loss is converting that spinning shaft into a moving stream of water. 2.) In general, waterjets are designed for high flow rates. They have a smaller diameter, but spin faster and move a LOT more water through them compared to a propeller. 3.) Yes, it is possible to design a waterjet optimized for slower speed and higher efficiency. It is called a pump jet, and most often used on submarines. I suspect they use the pump jet more for acoustic reasons, but the principles are still sound.
great video. btw, I was wondering how they design their impeller blades. is it just like an open propeller? is does it have a special geometry in it particular for its application?
They have a special design. Open propellers are limited to axial flow: water flows straight from front to back across the propeller disk. But in a waterjet, you have enclosed pipes and they can use centrifugal flow, which can be a huge boost in efficiency. Waterjets actually like somewhere between the two. The current trend is to create mixed flow impellers, which are a hybrid between axial flow and centrifugal flow.
Thx 4 this very educating video, which resulted in me to following question: when my jet noozle needs to be above waterline(which makes completly sense to me), how do i determine my waterline during design/construction?
i think your question is of boyancy aand also what your haul looks like, so a V haul would (when mooving) have a lower water line verses a flat bottomed boat. hope that helps!
Can you please Nick make videos about Towing Tanks?!, the accuracy of the results compared to the post sea trials? Different types of tanks and latest techniques?? Thank you
Okay, here’s a freebie……sort of!😜 You don’t like Bulbous Bows because of the thin parameters of usefulness? What if I had a way to negotiate that issue, and make it useful on almost any boat\ship you put it on?
Hi, I am working on a pedal bike design for pedal boats and thought that a waterjet that you could design for something like with a Bafang mid motor mixed with a Spatium water bike as example. I think the jet would be possible
Have you ever seen the old French Mirage jets? They had a "mouse" that moved forward and backwards to alter airflow. Could something like that be used to alter nozzle volume? Have you seen how Banks turbochargers work? What about that idea for altering waterflow?
In jet engines and I think large ship propellers, we know that moving a large volume of the medium at a slow speed is much more efficient than moving a smaller volume fast. That's why jet engines have huge fans now. I don't see this mentioned in water jets, but they must obey the same principle.
So if I understood correctly, all these outboard engines where a waterjet pump system replaces the prop driven lower unit, which are used on back of some boats for use in shallow water, are not being used correctly as the whole jet assembly is completely submerged ?
It would be more accurate to say they are not used optimally. Those aftermarket conversions could potentially be redesigned to work better. But sometimes we don't need things optimized to within an inch of perfection. I think those outboard waterjets are great at being a relatively affordable conversion kit to adapt to shallow water. They aren't 100% perfect. But sometimes, you don't need perfect.
What is your guys's opinion of a variable nozzle kind of like the afterburner of a jet engine. It could give you optimal flow angles through different velocities
I would like to thank you very much for your videos explaining how waterjet works and I am learning a whole lot. I am trying to design a kayak truster using an aluminum pipe of 2 inches diameter. If I want to create a nice jet what diameter would you recommend the nozzle to be? I came up with 2 inches to 1.5 inches reducer but I don't know how to calculate the ratio. would you be able to suggest something? Is 2 inches to 1.5 inches good enough compression or should I go from 2 to 1 inch? Thanks much
About the outlet jet : when you want to move forward, wouldn't be more efficient to push yourself into a back solid wall (water = higher viscosity) instead of a gas (air)?
No, because the waterjet doesn't push against anything. Many people think of that analogy of trying to push against something solid. But fluids work differently. In general, when you try to put something solid in the flow path, the fluid upstream senses the solid object and diverts around it, decreasing the overall efficiency of your design. Talking specifically about waterjets, you have to understand that the waterjet works by first building up pressure at the pump, and then letting that pressure drop back down at the outlet. Many other things also happen along the way, but the drop in pressure is critical. If I put a wall at the outlet (of water or a physical wall), that blocks the flow of water, holding in some of that pressure drop. This greatly reduces the efficiency of the waterjet.
@@DatawaveMarineSolutions Ok, thanks for your detailed explication! That means waterjets use the traction obtained from the pulling force of the propeller trough water (from front to back outlet) and throw up the pushing force obtained at outlet.. ??? Even that is weird for my brain, I think you are right (you are a marine engineer and I am just a construction one). But, as many others who won't belive before seeing it, I will make some tests in the next spring with both rigs. I am willing to build a kind of small catamaran pontoon boat and still not decided if to chose between electric or diesel/petrol motor and between regular propeller or jet, even hydrofoils. My heart goes for electric jet, but other says common old solutions are easier to implemment. P.S. sorry for my english 🙂
That's a bit of editing magic. The ring actually stays on my left hand the entire time. But sometimes I flip the image in editing to better fit in with the background. Just one of the many details that goes into forming these videos.
I notice editing anomalies in most media however I didn't notice the ring switch till you alerted me but if you look at the video at 2:48 his vest buttons are sewn on the right side of his vest and at 13:03 his vest buttons are sewn on the left side of his vest.Now we know he didn't resew his buttons. I bet he inverted some of his images in post production to fit his demonstration pics better.My wife hates that I notice this kind of stuff in the middle of movies. Great eye man!
None yet that I know of. Propeller research takes a long time and large budgets. We have to search through thousands of variations in propeller shape to correctly tune each prop design to the right flow conditions.
Not always. You lose a lot of efficiency when lifting 1-2 m. But it is not a sure bet that waterjets will be less efficient. It depends on the speed of the ship and the total distance lifted. It used to be that hydrofoils were preferred just because the alternative was very complicated propeller shafting to connect the engine in the hull to the propeller at the hydrofoil. Now, with more powerful electric motors, podded propulsion is an attractive alternative. Just run some high voltage wires down the struts into a pod on the hydrofoil.
Is it worth using a waterjet on a British NarrowBoat (60ft v 12ft flat bottom barge operating in very shallow water with a max speed of 7-8 knots) Traditionally propellers are used but get fowled up regularly due to water debris.
Hey mid design of some sort of board for water travel and ocean clean up in a fun way. Was wondering, does the angle of the impeller matter after the water jet is primed? my idea was to angle the impeller ( 45 dgrees maybe? for a guess) and have a larger then normal impeller, not deep inside the tube but closer towards to inlet, making a lower rpm possible, and washing away the cavitation! i figured that, if an impeller was angled, there would be a quick grab of the vehicle , so pulling down parralled to the angle of the impeller, but once primed the water jet then would still thrust forward. it'll be a personal water craft with very light parts, like an Eskateboard. the impeller could be mounted to shoot water straight up and fill a smaller tube directed out the back for thrust. i know i' have to test but some advice of the idea would help, think RC car that vaacuums at the bottom in order to drive up a wall, then a water shot out the back for propulsion! dope video, i'll definitly subscribe as i have quite a few water gadgets i have to develop! Thanks Jay Masters
hi , would it be possible to use water jets on a personal sub , i'm in the middle of working out which propulsion system would be best and also the kind of battery set up to put in it , thanks
Waterjets would not be recommended. However, you probably want a pump jet for a personal sub. For inspiration, you can look at tugs with ducted propellers. They use a very similar technology.
You stated that a fully submerged pump is BAD. So how does an efoil pump design work when placed close to foils? It is permanently submerged at that point. Does this mean they are highly inefficient? Commercial Efoils with jet pumps do exist now, so are they all underpowered/inefficient for torque and rpm specs similar to a prop driven efoil using same motor? Problem for me currently is that prop driven efoils are still illegal to use in Canada (but legal to sell). They must be a jet pump design to use without being fined $300. Thanks in advance.
I would not say highly inefficient. It depends on the difference in submerged depth. But the designs for Efoil jet pumps work slightly different from a boat waterjet. So there is no exact comparison. But practically speaking, any loss in efficiency still works out to a smaller cost than a $300 fine. The open prop isn't worth it for that case.
When a jet is working, its geometry is tilted, and so water comes into a chamber straight, and so exhausted with some angle into a surface. So, is it above or below a water line initially no more maters then imho.
Thank you Is there proven methods to instantly remove gas from water? Deaerators Henry's Law of Partial Pressure Thus removing cavitation and damage from gas implosion on the impeller ?
Nothing to absolutely prevent cavitation. Even if we completely remove all saturated gas, we still get cavitation. During cavitation, the liquid water converts to the gas phase (steam) due to low pressure. And then implodes a second later when the pressure rises again.
The entire waterjet is a single unit, from the inlet to the outlet. You seal the boat around the waterjet, and the waterjet casing seals out the higher pressure water. The only major point of water leakage is the drive shaft as it enters the waterjet case. (There are also some entry points for the hydraulics that steer the waterjet, but these are not in the path of the higher pressure water.) The drive shaft has a special bearing seal that works very well under high pressure. I can give you the details on that bearing, because that is not my field of expertise. Also, the waterjet pressure is not super high. This is no the same pressure as when they use industrial waterjets to cut steel. Boat waterjets operate at much lower pressures.
There one major flaw in this whole concept of waterjet, why use a middle/central shaft that gets in the way, and why not use a whole tube? Why divert the water to get inside in the first place ? Multiples outside spinning shaft can achieve much more power efficency then single central shaft. Also using multiple side shaft to spin the inner propeler means, you get more propeler surface, and no middle shaft in the way. Let the tube flow througj the water, as the water flow throw the tube. It's called a Tubemarine.
Also, you know bullet trains, how electromagnetic moves them. Imagine the rail is a ring, and inside that first big ring, theres a smaller ring that represent the train. You have a electromagnetic motorwheel. Now apply this concept to spinning a propeler inside a turbine and you have the best electric jet engine ever made. Now that you have all this, combine two Tubemarine, the concept of the hybrid hydrofoil and you have the best boat ever, eletricity powered. Now because you know there's always plenty off wind at sea, use a huge kite sail to futher increase the efficency of the boat. Voilà you've created a revolotionary boat design by combining already known stuff, just never put together before.
If you have problem understanding the motorwheel, or how to apply bullet train technologie to other motors, this video will explaib it to you th-cam.com/video/tNiY5y-jZFs/w-d-xo.html
I will add it to the list. A version of what you are describing is currently implemented on many modern subs. They call it a pump jet. Instead of an open propeller, they surround the propeller with a shroud and place some stators behind it. It uses many of the same principles as a waterjet. Although, designed for an entirely different purpose.
I was wondering if the principle of Dyson's bladeless fan concept can be used to propel water vehicle, especially a sub to reduce sound while increasing speed compared to conventional propeller design.
Excellent question. The full proper answer would be: It depends on the specific waterjet and geometry of the inlet. I would typically require a detailed CFD analysis to accurately answer that question. Disclaimers aside, the general answer would be: minimal propulsive effect. In a simplified jet design, the area of the sloped top on the inlet matches the area of the sloped bottom. Those two surfaces cancel each other. Now, some of the more advanced waterjet designs may try to change their inlet shape so the top and bottom areas are not equal. If you do it right, the increased pressure against the top of the inlet would generate a forward thrust. But you really need CFD to successfully make that an intentional design feature. The force on the inlet depends on the water flow, but the water flow gets shaped by the inlet. It's like trying to hit a moving target that actively tries to hide from you.
i wonder if anyone ever tought of putting a CVT gearbox on the back of the diesel engine. that way the diesel can run at its most efficient rpm ( 2000 rpm for example ) and the input rpm of the jet can be varied by the use of the CVT gearbox so basically the engine runs a constant rpm and then use the CVT to vary the jets rpm or have a variable outlet size like usd on military jet engines
@@DatawaveMarineSolutions depends on the cvt used . im not looking for one to go on a 50m ferry cat . more like twin 200hp diesels on the back of a 34 ft cat
Hi, does the power the engine has to produce depends on the speed of the water before or after the nozzle? I was wandering because the mass flow is the same but the speed is more at the end so that means more power? How is that posible
The power of the engine depends on the total change speed of the water, comparing inlet of waterjet to outlet of nozzle. You have to count from the inlet of the waterjet, not the nozzle, to capture the power produced by the impeller. But no matter where you count it, the power comes from the change in speed. The mathematics assume the water already flows through the jet, matching the forward speed of the boat. Without accelerating the water, no extra power is required. (Of course, the only way this could happen in real life is if the boat was towed.)
@@DatawaveMarineSolutions alright but if we use bernaulli, and the entry area of the waterjet is greater than the area of the nozzle ,that means that pressure will turn into speed , and more speed means more Thrust , but more speed change means more power or energy per l/s , but in pipes the water flowing tru a nozzle gets faster and looses pressure but where does the energy is coming from there? Is the pressure energy? So that means that the jetski pump when we add a smaller area nozzle need to produce more power to create more pressure?
@@alexindustries44 This is a case where Bernoulli's principle can be misleading. Bernoulli's principle only applies along constant streamlines, where the total energy in the fluid (pressure + speed, etc.) does not change. The impeller in the middle injects additional energy. There are effectively two zones that Bernoulli applies to, with a jump between the zones: before the impeller and after the impeller. The impeller generates a pressure increase without a velocity increase (at least the idealized version does).
hmm it's kind of interesting to see the nozzle trade off between speed and propulsive efficiency from rocket design also present in water jet design. IE: sea level nozzle need to be small so the exhaust pressure match the ambient pressure, while vacuum nozzle need to be gigantic because ambient pressure is effectively zero. There was some attempt to use an aerospike nozzle that turn the nozzle curve surface inward and let the ambient pressure form the shape of the perfect nozzle regardless of ambient pressure. Unfortunately aerospike nozzle didn't work out because rocket exhaust is way too hot, and aerospike has much higher surface relative to flow rate compare to a traditional nozzle. But in marine propulsion, I don't think cooling is an issue, so maybe aerospike nozzle could work in marine scenario, so you effectively have a variable shape nozzle that works for all speed.
@@sjoormen1 ahhh, well, it can help to know 3d especially if you intend to 3d print the parts. Though, as discussed here, doing paper calculations will greatly help.
16 core AMD EPYC with 32 GB of memory for simulations of less than 1M elements. For larger simulations, DMS also has a 32 core, 64 GB of memory machine. And for really large simulations, we have access to several computer clusters with hundreds of cores.
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Hi Nick, we just kinda met.... I'm still watching my first video, just paused it, then checked out your channel and I must say I'm happy to meet you. Very in-depth direct info, very well delivered with passion. Well done and I'm excited to learn more. Thank you.
man, thank you so much.. ive been trying to design a waterjet for some time and theres so little information on this subject online, and out of the blue comes this guy and answers every question i had
Waterjet for dummies. Deepest respects from a physicist and aviation inspector :)
My father, a boat builder in New Zealand in 1964, accepted Hamilton's, and the world's, first ever jet boat, as a trade-in. He passed it on to Hamilton himself. At the same time he was building a high country deer recovery, flat bottom, 25 footer with two Chrysler Interceptor V8s, with race cams and twin, four barrel, Holly carbs, totalling 800 horsepower. The fastest and most powerful of its day. It could carry a ton across wet gravel, fifty feet, and then into a foot of water.
I was picking my nozzle when my wife handed me a tissue and told me I was being gross . So when you pick your nozzle try to do it in private . DIY tip of the day .
Picking your nozzle and thrusting the axial flow into your bucket is such a drag. Great video, by the way!
I'm picking my nozzle currently 😁✌️
I am in tears. You saved my life with your deep wisdom. 🙏
You're the man. I'm from the Philippines and is designing a boat propelled by a jet out of recycled materials.
Great video. Basically confirms everything I already know. And how I know is about 12 years ago after years of racing rc cars I had decided to get into boats, but I wanted to custom build my own. Part way into build while researching stern drives I came across jet pumps made by a company called Graupner. Having a huge love for jet engines I was immediately intrigued. I ended up purchasing a 29mm jet pump with reverser for $80-90. It came completely unassembled so I had to put together which sounded easy (YEAH RIGHT!) Was a pain cuz there was only fraction of mm between impeller & side wall. So lining the drive shaft had to be PERFECT or impeller would scrape. Almost didn't think I was gonna pull it off but somehow I did. All I know is in the years since that thing has taught me ALOT about both the physics as well as the design of those amazing things lol. I still have it which I've installed into a "drive-box" that I use to demonstrate to people. It might only be 1 1/2" diameter and about 10" long but when coupled with a 40k rpm brushless motor it will shoot water 40-50 feet. Impressive little thing. All I know is mostly through observing it and the video essentially just confirmed it all.
I just found all your videos with this one. THANK YOU! I feel like I am being informed.
The first thing that came to my mind took me by surprise: This is way more more rocket science than your average boating. Instead of "biting into the water" prop style you are dealing with a reaction engine. Very intresting
But wait, all existing vehicles uses reaction principle to move. Every single one of them pushes something back to achieve forward motion.
@@shurmurray I'm refering to a reaction engine, like it expells mass at a (hopefully high) velocity as a means to gain direct propulsion. The faster it is thrown out = higher thrust, The heavier the matter it tosses out = higher thrust. A car uses friction to gain propulsion. A water jet (having a snorkle to continue to suck water) would keep accelerating just as well in free air because it is tossing a ton of water per minute out the backside at a considerable speed. A std boat propeller would be using the pressure differential I guess.
@@Paxmax the underlying principle is the same: vehicle pushes off something - either from a chunk of water or a whole planet. Or other way around: the impeller uses pressure difference in pumped water to produce thrust :) There is really not much difference beside external appearance and efficiency.
@@shurmurray Cars(tire friction) and boat/airplane propellers(pressure gradients) do not work in the vaccum of space, reaction engines do. It's kind of an important difference between the means of propulsion. If you have a big bag of water attached to the water jet it would create propulsion in space (if we disregard other circumstancial show stoppers such as a std combustion engine(normally powering the impeller) does not operate in vaccum and the water would tend to violently boil because of the lack of pressure).
@@Paxmax yes - all means of propulsion rely on some spare mass to throw backwards. Jet pushes water (gas, air...), car pushes the whole Earth. They can't move (change velocity) without that reaction mass - car without ground and water jet without water.
Attaching tank of water to a water jet to make it work in space - the same way we can attach a patch of a road to a car. Replace gravity with some magnets to ensure wheels are pressed against that patch of Earth - and car going to be able to increase it's forward velocity in space until the chunk of road ends and completely separates flying backwards.
Just today I was designing my waterjet and I had questions, like a light from heaven this video appeared, well in my search results. It's like he knew 4 years ago this day would come, uncanny.
Would variable angle of attack on the "fancy spiny thing" increase the efficiency range?
Thanks for all the videos Nick! Very informative.
Variable geometry exit nozzle? Maybe not like the variable exit nozzle on a fighter jet, but more like the air intake on the SR71 Blackbird. More suitable for mixed flow pump.
Nice thinking!
One thing that comes to mind when thinking about this is, "why not have the pipe inlet on the front to reduce drag from water changing direction up into the pipe?" At least, on something other than a fast planing vessel where only the bottom of the hull is in contact with the water. I am guessing the reason is that skin friction inside the pipe would be a much greater effect than the gain (discounting the fact that you also have to slightly enlarge your hull to maintain displacement)?
Excellent point. The trade off of skin friction in the pipe is a challenge to get around. One major concern is that we want the steering force in the aft end to maintain directional control. It becomes much harder with the steering only in the front end.
I use a variable nozzle that actually changes shape long the curve to maintain peak efficiency. I also use a variable inlet. I use a variable impeller as well which adjusts as speed increases. thanks for these videos they helped me come up with some great designs.
are your designs in the market? so I can take a look?
cant believe this video is free
im studying to be a mech e and this stuff is so fun to watch thank you
That was great idea for getting rid of, or rather actually keeping the bubbles to stop the damage. Something I would have thought out.
Thanks for sharing your video with us,
This is great information, I committed with a question on one of your past jet video, it’s almost like this one answered my question, the agency I work for is about to dump about 100k on a new trim setup, after they fail i will show them this video . Cheers
This is really helping me with autonomous/RC robotics water vehicles
I need to click on your earlier waterjet explanations to find out what sized ships can benefit from them as opposed to propeller drive ships.
Really informative video, Nick. You always make good stuff.
I had one question though. You say that discharging below the waterline is bad because of the higher external pressure. But wouldn't the elevation change increase the stagnation pressure in the water flowing out the nozzle by just as much, thereby canceling that effect out?
Excellent question. I had to think about this one. It's true that the change in static pressure is the same, due to the elevation change. But the dynamic pressure from the waterjet (equivalent pressure from the velocity) is much higher than just the static pressure. To make valuable use of that dynamic pressure, we need free flowing water from the outlet. Otherwise, the viscosity of the surrounding water and the static pressure slow down our outlet flow. It isn't strictly a matter of static pressures. It's also the momentum of moving that much water. We encounter less resistance if there is nothing in the way at the outlet.
@@DatawaveMarineSolutions That makes a lot of sense, thanks!
So much answers in this video. Thank you much!
The beginning made me laugh you got my sub bro good video
What if the stator blades double as the nozzle? The blades stop the rotation of the water and reduce the circumference for thrust. Remember, water doesn't like to be compressed. I had another thought: what if the impeller blades were spun by the outside (still inside the housing, just outside of the blades)? Maybe variable pitch blades too? This might help with the problems that hydroplanes face with the wings being under water.
I learnt a lot with this video, thank you!
However, I'm pretty sure all these constraints have been studied thoroughly and engineered solutions have been brought.
Being more an "artist" than an engineer, I was wondering if a few things would be mechanically possible/advantageous:
- a variable nozzle diameter (a.k.a. "iris door") to adapt the diameter of the nozzle to the speed of the impeller/flow/thrust: would it have some beneficial effect on any parameter? This would be pretty easy to implement with some electronics, but is it even relevant?
- floats both side of the nozzle to force it at a mostly constant level from the water line: Would the fold induced in the water path have a strong influence on the efficiency?
- a spoon-like cap (like on Pelton turbines) above the nozzle to redirect the outflow mostly horizontally instead of dispersing nearly vertically: would it waste thrust, or the gain would outweight the loss of thrust?
- the shape of the impeller: a few years back, Integza made tests on different shapes of impellers and came with a "lily impeller" (there's a ready-to print model on GrabCad). It would certainly make the path much longer, but is there a specific type of impeller to put in a water jet, or anything goes, it depends of the thrust and the engine power?
- for the inlet: to reduce turbulence, planes have winglets at the tip of the wings. Would putting fins near the inlets with the goal to drive and rectify the inflow work, or is it pure fantasy?
Thank you for sharing your views on this!
Thanks for putting sources down there 👍
Bow thruster advantageous and disadvantageous as for speed/torque to manoeuvre an object/overcome hidrostatic.
Hi there. Are there waterjets whose openings can be changed to match the speed like in jet fighter engines?
Same question! What about adjustable nozzle size?
That is exactly what I was thinking as well. It seems like some intermediate effect could be had with a simpler design than a fighter aircraft jet nozzle. Perhaps just some moving baffles which reduce the effective nozzle cross section, but do not direct the flow equally in all directions like a fighter aircraft (just balanced on each axis).
Yes, in theory you can change the inlet size to adjust waterjet performance with speed. In practice, I have never seen a commercial waterjet that does this. Too much complexity, and one more control that the captain needs to worry about. There may be some specialized military applications that do this. Military are the only people I can imagine who could afford the development cost of a custom waterjet design.
@@DatawaveMarineSolutions ahhh, ok. Thanks for the info, sir.👍
@@DatawaveMarineSolutions Surely if the only consideration is matching nozzle aperture to speed then software would manage it?
Good explanation and really motivating
Srilankan students have won international
competitions in waterjjets. That is why I
requested this.
can you point me to that competition so I can take a closer look? what were the criteria for winning?
Water is power source congratulations to everyone involved love sent in vibrations
Thanks for information about water jet .Simple.easy to understand
Are there nozzles that are flat/rectangular ? A rectangular outlet could very it’s output width.
Do you show somewhere an efficiency comparison between propeller vs. waterjet?
the baseline efficiency is always difference between ship speed and speed of accelerated water from the propeller or jet.....
I am also not quite sure what efficiency relation you are referring to in the slide shown?
To prevent cavitation, serialize dual impeller use 2 steps pressure increase.
Do they have to be exactly similar in size and shape for it to work, or would a progressive pitch angle work? Since water cant be compressed, they would have to be identical, right?
I want to make a water jet unit for a 19hp engine what diameter should the impeller be? Is there some sort of calculator of how to build it otherwise it will just be a spinny thing in a tube
Good video exactly what I was looking for
Thanks for the video.
It was very informative.
I was thinking of putting 3 x 16mm water jets in a cake tin (to be removed with ease) to screw on the bottom of a surfboard.
Gathering from this video it wouldn't work.
I want to make a motor to get a 9"7' longboard moving at a reasonable pace to have a bit of fun at the beach with the kids.
Any suggestions would be much appreciated.
Regards.
Mick
I think i would first try a single dc variable speed motor with a prop, maybe a motorcycle battery. If gas, i dunno, a moped engine? I imagine a ktm 50 might be a little peppy on a surfboard
Reccomended video currently under this one is: how to make 3d printed jet drive for surfboard
Great video as usual. Fascinating and compelling.
I am designing a surfboard with a water jet pump. I only need it to for short burst of energy. What I am trying to accomplish is a 5-15 second boost to help with catching the wave prior to take off. Where can I find water pumps to buy COTS type. Perhaps 1-2 inch diameter.
This information is so useful that I can better design 3D printing waterjet
i was thinking the same thing!
This is so educational.
Thank you for this information.
Because a lily shape propeller moves a larger mass of water for a fraction of the power of a conventional one, why are they not used?
Thank you, simple and smooth explanation
Very interesting vid! Thanks!
Where is the cavitation video you mentioned?
Here you go: th-cam.com/video/MyZzhwYMytc/w-d-xo.html
So I have a couple of questions:
1. Could the inlet be placed at the front of the boat to utilize the pressure created by the bow wave to facilitate water intake, reducing the distance the water needs to rise before ejecting from the nozzle, and allowing for a more interesting configuration of engines, pumps and nozzles?
2. Is it absolutely vital to have the waterjet at the rear of the boat? For example on a large displacement hull could the nozzles be placed on the sides of the hull above the waterline with buckets to control the flow fore and aft thus making even the largest of ships able to "strafe" without issue. If the waterjet is above the waterline it wouldn't interfere with hydrodynamics. My biggest concern would be bucket wear.
1. this is not a very good idea, you want to have the intake compleatly under water at all times to ensure that do dont have any air in the pump. the intake is formed so the water gets pressed in to the tunnel at speed, so you are using the movement of the boat to your advantage . what is also happening is that you create a flow of water close to the hull and this reduses the friction. In general all waterjet driven boats travel at speeds that are above "the hump". normally +30 kn.
2. Some special appilications do this. normally the "strafe" is a small part of manuvering. you need to have a efficent forward motion to reduce fule cost and get the top speed. if the side motions are important to that degree one could install a bowthruster quite cheap and get similar effect. If you move the jets to the side you get a lot of rotation of the ship. i know installations that use this for manuvering, mailny amphibious vehicles , its simple but not at all efficiant.
@@filipledin6548 Interesting.
With regard to point 1 though, what if you're talking about a large displacement hull where it's not above the waterline, the idea being to basically create a low pressure system at the front of the boat equal to the high pressure system creating the bow wave thus creating an even parting of the water down the length of the hull. No bow wave at all essentially.
I did the math, the idea is essentially to have a square bow and the area of the bow (in square meters) times the speed of the boat (in meters per second) equals the total volume of water (in cubic meters per second) that needs to be moved from the front of the ship to the back of the ship. Provided the jet is moving roughly that much water there should be no bow wave to overcome. Designing it so that it doesn't suck air, at least in calm water, shouldn't be too difficult I would think, then again this isn't my field.
@@samoldfield5220 I know some about jets, but im no naval architect what so ever. What i described is the general idea why its placed as it is and the logic behind it.
Great explanation :)
So now i have a question..
Im building an RC model of a yacht Project Infinty by Dorries yachts and because me being me this means that i'm not building a 1m model but a model that will be 3m long (1:30 scale) and i would like it to be powerfull enough to pull a skier on water (total weight of the model est. to be arround 120-130kg )
So how can i calculate how big impeller do i need and how powerfull engine to run it? (Im going to do it with dual jet powered by an electric motor
I'd be very gratefull for any sort of information.
Thanks
think of an impeller as a pop can. calculate the volume, then multiply by blade number. figure the wqeight of the water, then calcculate the speed of the water at the Nozzle coming out.
for example. pop can weighs 1LBS(just an example) thats the volume of your impeller times 3 for each blade, so 3 lbs. Depth of impeller is the water speeds plug in, if you have an impeller that is pitched(of deep/height of a cylinder) for one rotation its 3 pounds moving the hieght of your cylinder, then RPM is the speed at which it moves.
you have to calculate how much weight is pushed and at what speed in order to get your total force.
sorry its been a minute since i had to calculate it so the text is choppy haha! hope that helps for an idea of how to proceed with research!
Jetboards generally use a nozzle including stator vanes to increase waterflow velocity and efficiency. Commercial boards use boosterjet setup; the rider is controlling the board by shifting his/her weight.
What about the efficiency of a propeller as a semi jet propulsion unit?? A propeller style jet pump without the nozzle. I am curious. Can it be tucked under the watercraft like a jet pump and be efficient??? Could this be your next content??
Apreciate the educational videos.
Hi, would a Waterjet make sense for underwater propulsion (beneath the waterline) or would an old-fashion propeller be the better choice for that?
Strictly speaking, no. A waterjet is specifically designed for surface propulsion. There is a similar device used for underwater propulsion called a pump jet. These are popular on military submarines.
I'm a novice here. Trying to learn as much as I can from a physical standpoint. So I may ask silly questions. Every time I think of jet propulsion I think of how it compares to sterndrives, or propeller drive if you will, and why the loss in efficiency compared to the sterndrive. On outboard motors I see for example 60/40 horsepower. So 60 engine horsepower but only 40 horsepower at the impeller? Or is this horsepower being measured by a different means, like thrust? Because thrust can be converted to horsepower in the case of turbine engines so I assume that might also apply to waterjets as well. I can't comprehend how 20 horsepower would be lost from the crankshaft to the impeller since it's a direct connection. My only guess is 20 horsepower is consumed moving water through a narrow passageway under high pressure, and what we get in return is 40 horsepower worth of thrust, if that makes sense. Whereas as the impeller moves a "low volume" of water under high pressure and velocity, the propeller moves a much larger volume of water at lower velocity and "no pressure", so to speak. It's simply under the water it's only job is to move the water rearward the vessel......unless you're going in reverse.
First question, is my statement correct, at least partly? Second, theoretically, could a waterjet be designed almost opposite of most current waterjets today where it moves a larger volume of water at a lower velocity and pressure (to a point) like the propeller drive, and be closer to the efficiency of the propeller drive? Yes, I'm aware of the concern about cavitation. For now let us pretend it isn't a factor.
The point of all this is I do like jet propulsion but I HATE the loss of efficiency and speed compared to a propeller drive. I would love nothing more than to see the efficiency deficit addressed but until I do, I won't tolerate the loss in speed just so I can operate in shallow water.
You are mostly correct. 1.) yes, the loss in power is referring to the effective power delivered from the impeller. There is a tiny loss due to friction in the impeller shaft (2%-4%), but the major loss is converting that spinning shaft into a moving stream of water. 2.) In general, waterjets are designed for high flow rates. They have a smaller diameter, but spin faster and move a LOT more water through them compared to a propeller. 3.) Yes, it is possible to design a waterjet optimized for slower speed and higher efficiency. It is called a pump jet, and most often used on submarines. I suspect they use the pump jet more for acoustic reasons, but the principles are still sound.
great video. btw, I was wondering how they design their impeller blades. is it just like an open propeller? is does it have a special geometry in it particular for its application?
They have a special design. Open propellers are limited to axial flow: water flows straight from front to back across the propeller disk. But in a waterjet, you have enclosed pipes and they can use centrifugal flow, which can be a huge boost in efficiency. Waterjets actually like somewhere between the two. The current trend is to create mixed flow impellers, which are a hybrid between axial flow and centrifugal flow.
Thx 4 this very educating video, which resulted in me to following question: when my jet noozle needs to be above waterline(which makes completly sense to me), how do i determine my waterline during design/construction?
i think your question is of boyancy aand also what your haul looks like, so a V haul would (when mooving) have a lower water line verses a flat bottomed boat. hope that helps!
Can you please Nick make videos about Towing Tanks?!, the accuracy of the results compared to the post sea trials? Different types of tanks and latest techniques?? Thank you
I have those videos planned for production later this year. Stay tuned and they shall appear.
Okay, here’s a freebie……sort of!😜
You don’t like Bulbous Bows because of the thin parameters of usefulness? What if I had a way to negotiate that issue, and make it useful on almost any boat\ship you put it on?
Hi, I am working on a pedal bike design for pedal boats and thought that a waterjet that you could design for something like with a Bafang mid motor mixed with a Spatium water bike as example. I think the jet would be possible
What about inlet tube shape? Nozzle shape?- different shapes would make variable volumes much easier
New subscriber... Thank for tje video sir
Have you ever seen the old French Mirage jets? They had a "mouse" that moved forward and backwards to alter airflow. Could something like that be used to alter nozzle volume?
Have you seen how Banks turbochargers work? What about that idea for altering waterflow?
In jet engines and I think large ship propellers, we know that moving a large volume of the medium at a slow speed is much more efficient than moving a smaller volume fast. That's why jet engines have huge fans now. I don't see this mentioned in water jets, but they must obey the same principle.
Yes. Most waterjets do tend to use that principle.
So if I understood correctly, all these outboard engines where a waterjet pump system replaces the prop driven lower unit, which are used on back of some boats for use in shallow water, are not being used correctly as the whole jet assembly is completely submerged ?
It would be more accurate to say they are not used optimally. Those aftermarket conversions could potentially be redesigned to work better. But sometimes we don't need things optimized to within an inch of perfection. I think those outboard waterjets are great at being a relatively affordable conversion kit to adapt to shallow water. They aren't 100% perfect. But sometimes, you don't need perfect.
How can we calculate the power needed to push 1ton displacement travelling at 30k ots?
What is your guys's opinion of a variable nozzle kind of like the afterburner of a jet engine. It could give you optimal flow angles through different velocities
I would like to thank you very much for your videos explaining how waterjet works and I am learning a whole lot. I am trying to design a kayak truster using an aluminum pipe of 2 inches diameter. If I want to create a nice jet what diameter would you recommend the nozzle to be? I came up with 2 inches to 1.5 inches reducer but I don't know how to calculate the ratio. would you be able to suggest something? Is 2 inches to 1.5 inches good enough compression or should I go from 2 to 1 inch? Thanks much
About the outlet jet : when you want to move forward, wouldn't be more efficient to push yourself into a back solid wall (water = higher viscosity) instead of a gas (air)?
No, because the waterjet doesn't push against anything. Many people think of that analogy of trying to push against something solid. But fluids work differently. In general, when you try to put something solid in the flow path, the fluid upstream senses the solid object and diverts around it, decreasing the overall efficiency of your design.
Talking specifically about waterjets, you have to understand that the waterjet works by first building up pressure at the pump, and then letting that pressure drop back down at the outlet. Many other things also happen along the way, but the drop in pressure is critical. If I put a wall at the outlet (of water or a physical wall), that blocks the flow of water, holding in some of that pressure drop. This greatly reduces the efficiency of the waterjet.
@@DatawaveMarineSolutions
Ok, thanks for your detailed explication!
That means waterjets use the traction obtained from the pulling force of the propeller trough water (from front to back outlet) and throw up the pushing force obtained at outlet.. ???
Even that is weird for my brain, I think you are right (you are a marine engineer and I am just a construction one).
But, as many others who won't belive before seeing it, I will make some tests in the next spring with both rigs.
I am willing to build a kind of small catamaran pontoon boat and still not decided if to chose between electric or diesel/petrol motor and between regular propeller or jet, even hydrofoils.
My heart goes for electric jet, but other says common old solutions are easier to implemment.
P.S. sorry for my english 🙂
Great video. Off subject question....what's the purpose of the ring moving between hands during the video?
That's a bit of editing magic. The ring actually stays on my left hand the entire time. But sometimes I flip the image in editing to better fit in with the background. Just one of the many details that goes into forming these videos.
I notice editing anomalies in most media however I didn't notice the ring switch till you alerted me but if you look at the video at 2:48 his vest buttons are sewn on the right side of his vest and at 13:03 his vest buttons are sewn on the left side of his vest.Now we know he didn't resew his buttons. I bet he inverted some of his images in post production to fit his demonstration pics better.My wife hates that I notice this kind of stuff in the middle of movies. Great eye man!
Is there any research about the advantage to using toroidal shaped impeller blades in a jet system?
None yet that I know of. Propeller research takes a long time and large budgets. We have to search through thousands of variations in propeller shape to correctly tune each prop design to the right flow conditions.
i would make the active rotary vanes in rings composing the chamber, not as a air turbine in the center, where it blocks the flow...
In the case of a hydrofoil is it still more efficient to lift the water up above the waterline than to have it submerged?
Not always. You lose a lot of efficiency when lifting 1-2 m. But it is not a sure bet that waterjets will be less efficient. It depends on the speed of the ship and the total distance lifted.
It used to be that hydrofoils were preferred just because the alternative was very complicated propeller shafting to connect the engine in the hull to the propeller at the hydrofoil. Now, with more powerful electric motors, podded propulsion is an attractive alternative. Just run some high voltage wires down the struts into a pod on the hydrofoil.
Your intro 10/10 ape instinct
Why not have variable nozzles, like the garden hose, or a modern fighter jet?
Jet boards make all the floods more fun.
with standard bicycle gearing of course, 28 gears etc
Can nozzles resize themselves based on water pressure?
if the jet is above water, pushing against air wont push the boat forward??? :P
Is it worth using a waterjet on a British NarrowBoat (60ft v 12ft flat bottom barge operating in very shallow water with a max speed of 7-8 knots)
Traditionally propellers are used but get fowled up regularly due to water debris.
Hey mid design of some sort of board for water travel and ocean clean up in a fun way. Was wondering, does the angle of the impeller matter after the water jet is primed?
my idea was to angle the impeller ( 45 dgrees maybe? for a guess) and have a larger then normal impeller, not deep inside the tube but closer towards to inlet, making a lower rpm possible, and washing away the cavitation!
i figured that, if an impeller was angled, there would be a quick grab of the vehicle , so pulling down parralled to the angle of the impeller, but once primed the water jet then would still thrust forward. it'll be a personal water craft with very light parts, like an Eskateboard.
the impeller could be mounted to shoot water straight up and fill a smaller tube directed out the back for thrust.
i know i' have to test but some advice of the idea would help, think RC car that vaacuums at the bottom in order to drive up a wall, then a water shot out the back for propulsion!
dope video, i'll definitly subscribe as i have quite a few water gadgets i have to develop!
Thanks
Jay Masters
Awesome project. Were you able to make progress?
hi , would it be possible to use water jets on a personal sub , i'm in the middle of working out which propulsion system would be best and also the kind of battery set up to put in it , thanks
Waterjets would not be recommended. However, you probably want a pump jet for a personal sub. For inspiration, you can look at tugs with ducted propellers. They use a very similar technology.
You stated that a fully submerged pump is BAD. So how does an efoil pump design work when placed close to foils? It is permanently submerged at that point. Does this mean they are highly inefficient? Commercial Efoils with jet pumps do exist now, so are they all underpowered/inefficient for torque and rpm specs similar to a prop driven efoil using same motor? Problem for me currently is that prop driven efoils are still illegal to use in Canada (but legal to sell). They must be a jet pump design to use without being fined $300. Thanks in advance.
I would not say highly inefficient. It depends on the difference in submerged depth. But the designs for Efoil jet pumps work slightly different from a boat waterjet. So there is no exact comparison. But practically speaking, any loss in efficiency still works out to a smaller cost than a $300 fine. The open prop isn't worth it for that case.
When a jet is working, its geometry is tilted, and so water comes into a chamber straight, and so exhausted with some angle into a surface. So, is it above or below a water line initially no more maters then imho.
Thank you
Is there proven methods to instantly remove gas from water?
Deaerators
Henry's Law of Partial Pressure
Thus removing cavitation and damage from gas implosion on the impeller ?
Nothing to absolutely prevent cavitation. Even if we completely remove all saturated gas, we still get cavitation. During cavitation, the liquid water converts to the gas phase (steam) due to low pressure. And then implodes a second later when the pressure rises again.
Hey nice video but how do we seal the water from entering the boat at such high pressure
The entire waterjet is a single unit, from the inlet to the outlet. You seal the boat around the waterjet, and the waterjet casing seals out the higher pressure water. The only major point of water leakage is the drive shaft as it enters the waterjet case. (There are also some entry points for the hydraulics that steer the waterjet, but these are not in the path of the higher pressure water.) The drive shaft has a special bearing seal that works very well under high pressure. I can give you the details on that bearing, because that is not my field of expertise. Also, the waterjet pressure is not super high. This is no the same pressure as when they use industrial waterjets to cut steel. Boat waterjets operate at much lower pressures.
There one major flaw in this whole concept of waterjet, why use a middle/central shaft that gets in the way, and why not use a whole tube?
Why divert the water to get inside in the first place ? Multiples outside spinning shaft can achieve much more power efficency then single central shaft. Also using multiple side shaft to spin the inner propeler means, you get more propeler surface, and no middle shaft in the way. Let the tube flow througj the water, as the water flow throw the tube. It's called a Tubemarine.
Also, you know bullet trains, how electromagnetic moves them. Imagine the rail is a ring, and inside that first big ring, theres a smaller ring that represent the train. You have a electromagnetic motorwheel. Now apply this concept to spinning a propeler inside a turbine and you have the best electric jet engine ever made. Now that you have all this, combine two Tubemarine, the concept of the hybrid hydrofoil and you have the best boat ever, eletricity powered. Now because you know there's always plenty off wind at sea, use a huge kite sail to futher increase the efficency of the boat. Voilà you've created a revolotionary boat design by combining already known stuff, just never put together before.
If you have problem understanding the motorwheel, or how to apply bullet train technologie to other motors, this video will explaib it to you th-cam.com/video/tNiY5y-jZFs/w-d-xo.html
Are there any nacelle style water jets that look like submerged aerojets?
Layman here: Can you make a video about the prospect of submarine jets?
I will add it to the list. A version of what you are describing is currently implemented on many modern subs. They call it a pump jet. Instead of an open propeller, they surround the propeller with a shroud and place some stators behind it. It uses many of the same principles as a waterjet. Although, designed for an entirely different purpose.
I was wondering if the principle of Dyson's bladeless fan concept can be used to propel water vehicle, especially a sub to reduce sound while increasing speed compared to conventional propeller design.
I have also wondered about this. At this stage, I can not say. It would require a detailed analysis to answer that question.
What propulsive effect does one get from the force of the water pressing against the sloped top of the inlet?
Excellent question. The full proper answer would be: It depends on the specific waterjet and geometry of the inlet. I would typically require a detailed CFD analysis to accurately answer that question.
Disclaimers aside, the general answer would be: minimal propulsive effect. In a simplified jet design, the area of the sloped top on the inlet matches the area of the sloped bottom. Those two surfaces cancel each other.
Now, some of the more advanced waterjet designs may try to change their inlet shape so the top and bottom areas are not equal. If you do it right, the increased pressure against the top of the inlet would generate a forward thrust.
But you really need CFD to successfully make that an intentional design feature. The force on the inlet depends on the water flow, but the water flow gets shaped by the inlet. It's like trying to hit a moving target that actively tries to hide from you.
i wonder if anyone ever tought of putting a CVT gearbox on the back of the diesel engine. that way the diesel can run at its most efficient rpm ( 2000 rpm for example ) and the input rpm of the jet can be varied by the use of the CVT gearbox
so basically the engine runs a constant rpm and then use the CVT to vary the jets rpm
or have a variable outlet size like usd on military jet engines
I suspect it was considered. Main problem, we push so much power through these power trains that a CVT would probably burn up.
@@DatawaveMarineSolutions depends on the cvt used . im not looking for one to go on a 50m ferry cat . more like twin 200hp diesels on the back of a 34 ft cat
Nice video man!
Very good!! Thanks for share!!
Hi, does the power the engine has to produce depends on the speed of the water before or after the nozzle? I was wandering because the mass flow is the same but the speed is more at the end so that means more power? How is that posible
The power of the engine depends on the total change speed of the water, comparing inlet of waterjet to outlet of nozzle. You have to count from the inlet of the waterjet, not the nozzle, to capture the power produced by the impeller.
But no matter where you count it, the power comes from the change in speed. The mathematics assume the water already flows through the jet, matching the forward speed of the boat. Without accelerating the water, no extra power is required. (Of course, the only way this could happen in real life is if the boat was towed.)
@@DatawaveMarineSolutions alright but if we use bernaulli, and the entry area of the waterjet is greater than the area of the nozzle ,that means that pressure will turn into speed , and more speed means more Thrust , but more speed change means more power or energy per l/s , but in pipes the water flowing tru a nozzle gets faster and looses pressure but where does the energy is coming from there? Is the pressure energy? So that means that the jetski pump when we add a smaller area nozzle need to produce more power to create more pressure?
@@alexindustries44 This is a case where Bernoulli's principle can be misleading. Bernoulli's principle only applies along constant streamlines, where the total energy in the fluid (pressure + speed, etc.) does not change. The impeller in the middle injects additional energy. There are effectively two zones that Bernoulli applies to, with a jump between the zones: before the impeller and after the impeller. The impeller generates a pressure increase without a velocity increase (at least the idealized version does).
@@DatawaveMarineSolutions now i got it ,that makes a lot of sense thank you for the answer
hmm it's kind of interesting to see the nozzle trade off between speed and propulsive efficiency from rocket design also present in water jet design. IE: sea level nozzle need to be small so the exhaust pressure match the ambient pressure, while vacuum nozzle need to be gigantic because ambient pressure is effectively zero. There was some attempt to use an aerospike nozzle that turn the nozzle curve surface inward and let the ambient pressure form the shape of the perfect nozzle regardless of ambient pressure. Unfortunately aerospike nozzle didn't work out because rocket exhaust is way too hot, and aerospike has much higher surface relative to flow rate compare to a traditional nozzle. But in marine propulsion, I don't think cooling is an issue, so maybe aerospike nozzle could work in marine scenario, so you effectively have a variable shape nozzle that works for all speed.
Now that is a very interesting idea!
Now I just need to learn 3d design software so I can design a jet for RC boats.
every software is good just as man behind computer is.
@@sjoormen1 ahhh, well, it can help to know 3d especially if you intend to 3d print the parts. Though, as discussed here, doing paper calculations will greatly help.
Agreed. Just seing that withoit knowledge computer dosen't help much. Yet.
Blender is a solid program, but i think a CAD one for design is better, as a lot of design for parts is repetitive
witch propeller use for moto engin 110cc ?
What if you change where the water comes from?
What kind of computers do you use to run FEA?
16 core AMD EPYC with 32 GB of memory for simulations of less than 1M elements. For larger simulations, DMS also has a 32 core, 64 GB of memory machine. And for really large simulations, we have access to several computer clusters with hundreds of cores.