It is partially the load and partially the extreme speed. But drag boats typically use surface piercing, super-cavitating propellers (also called surface drives), which are an entirely different beast from conventional propellers. The main goal of surface drives is to minimize the area of propeller in the water, because at those speeds, the propeller produces significant drag in the water. With a surface drive, typically only the bottom half of the propeller is in the water.
Every time I have an obscure marine engineering question, DMS Marine pops up with the correct answer. I love it. The details on velocity ratio and relative application speed where right on target for me. It makes sense from a fluid dynamics perspective, but sometimes when you just have boat lust, you forget the basics. A little like those new toroidal props the kids are making for drones. There are certain advantages, but a much smaller optimized operating range. sorry, I nattering. Thanks for an awesome set of videos. It's a lot of work and they continue to amaze.
When I watch your videos I have no idea what decade I am in. I guess in a way it makes your information even more timeless. Thanks for the great content and details.
1968, patrol boat river. My first contact with jet drives. Twin v-6 Detroit diesels, Jacuzzi jet pumps. As I recall. 32 feet long, the jets made us think we knew what we were doing. Easy to maneuver in tight quarters, also in wind and current. Swore I would have one when I got back to the world. Then I found out what they cost, back to oars.
I just got back from key West Florida and in the shallow Waters I saw many carved lines in the coral created by boat propellers. I guess the jet propulsion also has an advantage there.
Thank you, this addressed the questions I had without me needing to wade through the advertising hype. I've been enjoying your channel. Have a great day.
It has been a great use of my time watching your video, I love the way you explained keeping it simple. Just wanted to comment, I have read (actually You tubeing) and it seems that there is an alternative to the gray area of 20-30 knots regarding efficiency (I do not think for maneuverability). The so called Advanced Propellers by Maarten MOSTERT that claims the fuel reduction by increasing propeller efficiency up to 20%. The other is the Voith Linear Jet, they states that has better efficiency than water jets up to 40 knots. Both above options with simple maintenance as a conventional propeller (who has waterjets know about its maintenance, specially when marine life give a pain in the neck. I may say it is worth to compare all three systems in the 20-30 knots. Thanks and keep the excellent work
I agree. I knew about the Voith linear jet, but the Advanced propellers were new to me. Thanks for the information! advancedpropellers.com/ Eventually, I hope to make a video discussing the options in the transition region.
as long as there are not a lot of leaves on the bottom, for the jet to vacuum up. saw that on a jet powered kayak. guy was in shallow slow moving creek, kept having to stop amd clean out the intake svreens. yes i like jets better in the shallows or arpund stumps, dont forget to pull the locking pin on your outboard so they motor cam come out of the water when it hits something...
Nothing is really good in very shallow water. Jets suck up stones, sticks, sea weed, and all kinds of things that can damage them. That's easier than you think, shells are nasty on the impeller, chipping the shit out of everything. They do go slightly shallower, but not much. Fast application is a little different, but still, not that much if preservation is your goal.
Hi, I am new in this excelent canal, very ilustrative! My question is the following: I have in mind to use a fast boat with a capacity of 20 passengers and I would like to understand what type of water jet pump should I use and what engine? I have in mind a super charged diesel engine, preferably due to the basically cost of fuel here in Peru. I need recommendations to have a better understanding of engine ratio, weight, speed. The intention is to take visitors through the rivers of the Peruvian jungle at relatively more efficient speeds than outboards and basically thinking about shallow rivers where outboards are inefficient. thanks for your comments......
You mentioned the waterjet has a lower intake than the vessal and from what i understand this is what hinders it from being able to produce the proper thrust at lower speeds... What if the inlet for the jet was mounted on the sides of the vessel but still below the water line to insure no air entered the jet when at full speed? Or maybe installing ram scoops to help pull the water in as you pick up speed so you could start out slow but as you move the scoops help pull in more water amd increase the efficiency? Just a thought.. :)
@@KKhhoorrnniittee No, only a few of their models, possibly only one right now. I mean from Pershing 6x to 9x they use surface drives and thanks to that they're so fast they could get from Odessa to Snake Island in no time! I think right now The 140 is the only one with jet drives, making it a lot faster than huge ships like the Moskva...but then again all boats are faster than Moskva since it's in the bottom of the Black Sea along with a pretty good number of orcs.
There is a local river where I live that goes from 20+ ft deep to 6 inches deep all along its length. Its nothing but a series of pools and shallows with a gravel sand bottom. Jet boats are the only type of powered boat that can be used on it. Most people have a wide shallow draft flat bottom boat with a outboard jet.
Should add discussion on cavitation. Waterjets operate best under laminar flow. If too fast and there is excessive air, they don't work, as thrust is reduced. Same with Propellers. The speed limit for a blade going through water is around 50 to 55kts where cavitation occurs. Once you hit cavitation speeds, you lose thrust over any propeller or impeller. This includes obstructions from badly designed brackets and hull designs. Water jets do not work with stepped hulls, where the step adds air under the hull that can get ingested into the water jet.
One problem not mentioned sea weed , floating grass caught up on the intake grates needing to be cleaned often . Perhaps they have an auto system that cleans the intakes .
Great question. Unfortunately, too complicated for a simple TH-cam video. That would require a detailed trade-off study. Let me know if you ever want to contract DMS for that work.
What would use more fuel? Crossing the Atlantic at 14 knots with a conventional propeller, or crossing it at 30-35 knots with a waterjet? That would be a huge deciding factor I would think.
Slow is definitely more efficient. Not to mention it's very unlikely in an Atlantic crossing to have conditions suitable for 30-35 kts. Even in a big yacht you're forced to go slower due to sea state more often than you'd realize.
I agree, although planes try to minimize the speed to increase the efficiency (more flow less speed), and here they apparently find efficiency at higher speeds.
I wouldn't say minimising the speed of an aircraft optimises efficiency. After all, in most applications your efficiency is in terms of fuel used for distance travelled, and the design of an airframe and engine combination has a distinct point of maximum efficiency at which both faster and slower speeds are worse. Plus, props, turboprops and turbofans all have other constraints. A turbofan is more efficient in lower density air, thus it encourages flying at higher altitudes. Indeed it's not usually very effective flying below 30,000 feet with any kind of jet engine. conventional props meanwhile, lose power with altitude to the point that you likely wouldn't even be able to get most of them up to 30,000 feet... For most low speed applications a prop is likely more efficient, but it also has more mechanical wear and tear, and it's difficult to achieve high speeds without a very large and heavy engine. In aircraft there is of course a major transition point - supersonic airflow; Once the airflow goes supersonic, the physics change. This means you either want something to be entirely supersonic, or not at all. When parts of a system are moving through air at supersonic speeds but not others, bad things tend to happen. This is one of the limitations on prop aircraft, but it's also why a turbofan is more efficient when it spins slower; It's not because you're trying to make it slower in general, it's that you want the fan diameter to be as large as possible without the fan tips hitting supersonic speeds. The core of a turbine however, operates best at high speed. This means there's a tradeoff between the speed of the turbine, and the speed of the bypass fan. Since in most designs these are directly coupled, the faster the turbine, the more power the engine produces, but because the bypass fan produces most of the thrust, the bigger the fan the better... Until the fan tips reach supersonic speeds, at which point you either have to slow down the turbine, or use a gear box, which adds weight and complexity...
Sorry, but an exact motor sizing is considered contracted work. I recommend you look at some Zodiac boats (www.zodiac-nautic.com) to see what motor size they use on a comparable boat. Compare the boats based on length and beam, rather than seating capacity.
recall a 18' jet boat with 10 people onboard that had lots of engine noise but not enough thrust to put it on plane. Very embarrassing for the owner. He finally resorted to just puttering around the harbor.
What do think of pumpjets as used on submarines and are now available for yachts/commercial shipping. Voith in Germany now offers them and I wonder if they are a good comprise if draught is an issue.
I have aspirations to build a folding trimaran but I really hate that most have an outboard hanging of the transom - really spoils the aesthetic not to mention can't help with the weight balance. Seems straightforward to me to have a small jet drive with a motor placed more centrally. They can sail at 20 knots so maybe not too much of a dent in efficiency and anyway would be sailing most the time.
I could care less about efficiencies simply because I like the outside of my boat to be smooth without something hanging down that can get caught on things and possibly damage wildlife or get damaged itself or in the case of running aground, acting like an anchor.
We had a couple of WJ boats back in the 1970's. Both were 21 foot, both Ford 351, the workboat carried heavy loads and had a single stage 10 inch jet, the other boat was more pleasure and used a 3 stage 6 inch jet, both made by Hamilton Jets here in NZ. The 3 stage was faster, but the 10 inch single had the least speed change when loaded.
Good video . Question : should large hospital-ships not be installed with waterjets ? Wouldn't fast deployment and mobility not be a plus for changing global and distant geografical use when quickly needed in situations of emergency at big disasters ? Would also the combination of waterjet-propulsion and hydrofoil-hull not result in the fastest possible distant deployment for a hospital-ship ? Are such vessels already being built and thought of in terms of design ?
Yes, fast deployment would be a major advantage for hospital ships. Waterjets are one way to achieve that. The hydrofoil hull could create faster deployment, but there are other factors to consider. What you described is a ship that can respond to disaster scenarios. In addition to being a hospital ship, it also needs to provide logistics support to a disaster region. Flying in food, tent shelters, supplying fresh water, supporting helicopters to carry wounded back to the hospital. All that adds up to a lot of weight, and hydrofoils are not good at carrying large amounts of weight. Further, hydrofoils add a lot of draft, which would restrict the ship to only enter deep water ports. A flexible disaster response needs to be more like the Wasp-class amphibious assault ship: able to deploy anywhere you have a beach. To my knowledge, no one has plans to build such a vessel. This would be an expensive ship. And you can only justify that expense if the vessel sees use 80% of the year. Disasters don't strike that often.
Hoping this question wasn’t already asked or is plainly obvious: When you say ‘velocity’, I believe you mean the velocity of the boat, not the water that is jetted out. For your example of the large barge, with a smaller jet at high RPM, the water exiting the jet may be 30+ knots (limiting factor being cavitation along with impeller efficiency), while providing modest thrust for the large mass thus the barge may travel at say 5 knots. My question is, am I right to conclude that the efficiency is related to the velocity of the jet, not the boat itself?
Jet efficiency depends on a host of design factors. But if we ignore all the other design factors and just focus on speed, efficiency generally goes up with water velocity at the inlet of the jet. When a boat has forward speed, that forward speed helps to supply much of the velocity at the inlet. So technically, jet efficiency is tied to velocity at the inlet. But inlet velocity is also tied to forward speed of the ship.
I find it interesting, you talk about DMS in the 3rd person, yet Nick you are DMS, according to your website you are the only staff member, so drop the 3rd person and talk about your company as it is yourself and no one else.
By far the Biggest reason i bought a water Jet driven boat was Safety, B4 they had the safety strap on outboards didn't see this thank God but heard of this accident involving the death of two innocent kids when a bloke hit a wave was thrown overboard as his boat was racing out of control, after that i knew i would never again have a prop driven boat and as you rightly said the boat jet combination has to be right had a 14. 6 inches dateline with a V6 driving a PP6 jet unit combination was not the best as the boat would struggle to get on the plane facing the sky engine screaming doing 12 knots then once on the plane same RPM would do about 28 -30 knots topping up at just over 40 the other was about 17 food same engine very well marinized by Castolti jets Milan Italy driving a 09 jet the jet unit had a reduction gearbox build into it to suit any engine of your choice getting on the plane was totally effortless the PP6 jet was definitely better at high speed maneuvering but its impeller size was too small, it also had no build in gearbox n at times was wasting engine torque, same time it was a Lot cheaper to buy so overall both gave good value for money, speed boats are usually used for water skiing n fast fun boating so for me on all the issues water pumps are my choice too good video thx
I see these "performance" boats with five or even six outboard engines, can these five or six props really get enough water to realize potential or is this just to look good?
I'm thinking the same. What happens to the whole system in a rough see if the inlet is lifted clear of the waterline and it sucks in air? Presumably it'll unload and overspeed and need some sort of control to manage it.
This is a trimarand question. Why are the outer hulls always higher than the center hull, it makes the boat rock/handle like mono hull. I plan to build a trimarand where all hulls are equally in the water and supporting the boat.
It depends on the purpose of the trimaran. For what you described, those trimarans are trying to optimize for speed. Placing the outer amas higher does two things: 1. Reduces the draft of the outer amas and reduces their resistance to help the boat go faster. 2. Placing the amas higher means they provide buoyancy over a larger range of heel angles before becoming fully submerged (the point when things get bad for a trimaran). Other trimarans do exactly what you are suggesting. More important than the draft of the amas is their relative displacement and waterplane area compared to the center hull. Larger amas make for a stiffer / more stable ride.
Can you please do a video on the thunder child 2 hull? If you can't do a video specifically on it could you please do one on some of the technologies it uses. It is an extremely visual striking design that also seems to be very good at what it is meant to do.
Frank Kowalski, the father of that hull, described it as an asymmetrical catamaran (being such in the stern and tapering off to single hull in the bow) with a foil in the aft (between the catamaran halves) to promote planing. Oh, looks like we have a hybrid of two hybrids there {scratches head in confusion}. Definitely worth hearing a professional's opinion from a scientific standpoint.
Have anyone tested a combination of water jet propulsion and propellers? For example waterjet engine in the middle and two IPS engines on each side? You could program the waterjet to turn off between 8-25 knots for efficiancy
You can see a demo here with hamilton waterjets: th-cam.com/video/RryL3XwUO50/w-d-xo.html Crab walk only works with two or more waterjets. The buckets need to be set with one jet providing forward thrust, and one providing reverse thrust. Set your waterjets at opposite helm angles. Then the forward and aft thrust cancels out. Net result: sideways thrust. Practical example: say you want to crab to starboard. 1. Set the starboard jet for forward thrust, jet angled port. (The physical jet on your stern. The bucket swings toward the port side.) 2. Set the port jet for reverse thrust, jet angled to starboard. 3. If you carefully balance the buckets, the boat crab walks to starboard. This will probably require a high RPM, because most of the waterjet power cancels out. It's only a small component that gets directed sideways. I would definitely practice in away from the dock the first time you try this. **Many boats have linked steering. You can't individually control the jet directions. In this case, still use the opposite jet thrust. It still works, but not very well.
I have a 1979 glastron carson, I'm looking to change it to a twin water jet system with jetski motors. The question is who sells the kits on water jets.
My question relates to the efficiency of the water jet. I only know what I saw watching your TH-cam video about water jet propulsion systems. Your claim of 90% efficiency sounds great and should help with using the water jet on a solar fuelled boat. I am thinking that an efficient electric motor could turn the pump. Do you have any experience in this area? I am in the brainstorming step on picking a propulsion system that I hope could be run by solar and a backup generator if the sun is not out on a 30 foot catamaran. I would be replacing an inboard Volvo 220 engine. I am hoping with the more efficient batteries and motors I can find a really efficient propulsion system. Otherwise stick to the same old technology the boat normally comes in.
The 90% efficiency only relates to the pump, not the waterjet as a whole. The waterjet as a whole will be around 40% - 55% efficient. At low speeds, the efficiency can drop down to 30%. The pump efficiency only measures how well the pump converts the energy of a spinning shaft into a pressure difference. The waterjet as a whole then converts that pressure difference into forward thrust. I have done a fair amount of work on electric propulsion. I would not recommend a waterjet for electric propulsion. Waterjets are best suited for high speed, high power applications. Modern batteries are not ideal for high speed or high power.
@@DatawaveMarineSolutions Thank you for your quick response. Speed is not my goal other than say 20 to 25 knots when needed but long range efficiency using batteries capacitors and charged by generator, solar and 50AMP charging stations at the dock. So you reduced my options to stern drive and inboard outboard propulsion systems. Thank you. I really enjoy your videos. I would love to see one on converting stern drive engines say a Volvo 220 to an electric motor.
You can also consider the effect on wildlife. Driving a jet boat through spawning grounds of certain types of fish is like putting the eggs and fry through a blender. Drive through a mass of certain types of jellyfish and you can exponentially increase their population. The point is, consider the environment you'll be using each type of propulsion in, or your boat may last longer than where you intend to use it.
The advantage of a waterjet I'm looking for is the safety. A jetski could never be safe with an open prop. But I would like to go slow. I'm thinking of more like a prop in a tube, I haven't seen designs like this, must be a reason..
Another great video thanks. A question I've always been curious about is why don't Mono hulled sailboats have out riggers (not counting multi hull vessels). Is there any problems with retrofitting your own, like?
Because it would not help top speed, seakeeping, room aboard or much else. It would help righting moment, but all of the rigging and hull would have to be modified and strengthened, since there is no way for sudden gusts of wind to be unloaded from the boat by heeling, and it would not be able to go any faster with all of that extra power because would generally slam right into it hull speed anyways, just maybe a little quicker if that extra power could overcome the extra weight and appendage drag. It would be akin to training wheels on a bike. Help it stay upright, but extremely limiting everywhere else.
@@nicholaycalhoun1681 Thanks. I have a plan for refurbishing with the focus being to be as sea sound as possible. It's an interesting point about how the rigging in gusts that I hadn't thought about. Thanks again.
Heel angle on a monohull sailboat is actually beneficial to the hull efficiency. The water line gets longer so the boat can go slightly faster before hitting hull speed and wetted surface area actually decreases up until about 20° of heel in modern designs which reduces drag.
Liked the video thanks for the education, new sub here . I have a question to ask you , I work for a company that services boats . The agency who owns a boat that has twin Volvo diesels can’t stand the 46 ft v bottom that just nearly won’t plane . I think top speed is about 21 kts. They can’t see over the bow it’s bad. Twin jets , I believe they are hameltons . Do you have a clue where I can start? It’s a shame to see it sit and not get used .
Sounds like boat is trimming to far aft to get past its hump speed. I would try adding some interceptors on the transom. (Assuming you have any room between the jets.) Other tricks: look for objects on the boat that you can move forward (furniture, spare equipment, people, etc.). If that doesn't work, DMS offers professional engineering services. For the right price, I would be happy to look into the issues with that boat. You can contact me at sales@dmsonline.us Hopefully some simple adjustments are all that you need. Good luck.
Why can't you put water jets more under water? Aren't the rooster tails a sign of inefficiency? What if you mounted them at a 10 degree down angle to push against hard water? Wouldn't that make them more efficient? Thanks!
No physics stop them from going underwater. But they would be less efficient. Jets look inefficient because our brains are trained from looking at propellers. But waterjets work entirely different than propellers. They have their own set of rules. That rooster tail is actually a sign that waterjets works like intended. We want a massive jet of high speed water out the back. It generates the momentum that pushes the boat forward. Without that rooster tail, we don't get the momentum. Same way, if we put the jet underwater, the surrounding water would leach off the momentum of the jet, stealing our thrust. And if we mount at a 10 deg angle to push against hard water, it wouldn't do any good. We use the momentum of the water jet as it exits the bucket. Once the jet of water leaves the bucket, we gain no benefit from it. Pushing against the water can't help. The most efficient way to run a waterjet is straight, level, and just barely above the waterline.
@@DatawaveMarineSolutions This tracks. When Bill Hamilton invented the waterjet his prototype had a submerged nozzle. It did work, but it was very slow. Simply lifting the nozzle to be around 85% above the waterline provided massive speed gain.
Thank you for explaining, when to use these different technologies. I am curious if these water propusion theories also applies to small watercrafts, lets say a small one man ship or even rc boats big/small? Afaik the physics should not change drastically. -Regards a non native english speaker.
Yes, they apply at any size. But at smaller scale, it is easier to overcome inefficient propulsion with more power. So efficiency is less critical at smaller size.
So what's the difference between a propeller and impeller? Don't they both create a pressure difference to make thrust? The waterjet thing seems to me just a ducted propeller, but with a long duct (tube). Is it maybe like wind turbine blades where some are lift-type and others are drag-type?
Ducting a propeller increases efficiency and thrust. An impeller in a jet pump unit is effectively an optimised propeller for that application. It also uses stators etc to increase efficiency as stated in this video. Thrust is created by the volume of water passing through the pump and exiting the nozzle. The nozzle is located at or slightly above the waterline to take advantage of the differential density of water vs air thereby giving the pump the ability to move larger quantities of water accellerating the boat. There is more to it when calculating speeds flow rate of the pump and exit nozzle diameter all play a part. The jet pump has been around for some time but was not used so well until a NZ farmer by the name of Hamilton took the idea and moved the nozzle to the right location and created the first jet boat as we know today.
Both impellers and propellers do both create a pressure difference. But they exploit different ends of the pressure equation. For both a propeller and impeller, you get two changes in the water flow: a change in water pressure, and a change in water velocity. A propeller tries to minimize the change in water velocity. It wants to only have a change in pressure, keeping all the pressure change happening right at the propeller blades. Any other changes are lost energy. A waterjet uses a duct after the impeller. And that duct is crucial. It converts the generated velocity energy into back pressure against impeller blades, generating thrust. That means we can operate at higher speeds, generating lots of velocity change and still using that energy.
@@DatawaveMarineSolutions referring to a propeller as a screw would help explanation. A water jet is a water pump on crack that moves massive amounts of water at high pressure. A prop pulls through the water like screw threads. Them old timers were pretty precise with nomanclature.
@@DatawaveMarineSolutions , great video, the main thing that I feel you may have overlooked with this kind of propulsion is the fact of how they operate in "skinny" water . this is a major concern in Alaska gillnet fisheries and 3-4 feet of additional draft with conventional screw propeller can make a huge difference , if you can see a seagull's knees you have enough water to travel and commercial fish with a waterjet, huge over looked value of this type of propulsion thanks Jeff
Why is a water jet not submerged? I'd expect that output pushing against the water to be more efficient. With the output above water you only get Newtons action-reaction force.
Thanks for the content. Are the graphs from the video from [ J. Carlton, Marine Propellers and Propulsion, London: Butterworth-Heinemann Publications, 2007. ] ---> this source? If it is not, can you please inform me regarding that matter? Thank you.
What about if it's under the water for low speeds propulsion say up to 12 knots, wouldn't this be better make it more efficient. I mean you've got the back force of the water behind the impeller nozzle to propel you would it help at low speeds if you made a nosey go from above the water to below the water at its optimum speed. And what about the impellers automatic adjusting of Pitch as well for the given circumstances speed thrust
I can't say with certainty. What you are asking requires some very intensive waterjet optimization, and those are the details that a waterjet manufacturer never releases. Most of these jets end up partially underwater at low speeds. Usually, the waterline rests right on the shaftline of the jet. But even if fully submerged, that may not improve efficiency. The jets have an impeller, followed by guide vanes, followed by a bucket. The guide vanes and bucket all add drag, decreasing the efficiency. We can afford drag penalty at high speeds. But at low speeds, the margins we don't have that much thrust to start with. I also don't know of any impellers that allow automatic pitch adjustment. Most impellers are more like turbine blades. They are a single cast piece of metal, machined with high precision. They don't have any moving parts. You just attach them to the spinning shaft inside the waterjet. But that would be a neat feature if a waterjet included automatic pitch adjustment. Have you seen this on a specific model?
Take a look at Sir William Hamilton's performance figures for the first 2 water jets in a boat, both jets were used on the same boat, the boat was slow, the first jet discharged under water and the second above water, and it propelled the boat a twice the speed. You can test this by holding a reduced size nozzle water hose, then dip the nozzle under water, and see how the trust diminishes.
Has the "bucket" style thrust reverser ever been implemented in a power driven installation? Especially on a smaller pleasure vessel that thrust reverser method does not need to be bespoke.
I do have a question although I not a potential customer. Would water jets help a sailing yacht during low wind performance or during high waves in storm conditions ? Thank you I am a curious person
Yes, they would. Although any propulsion device will help a sailing ship at those low speeds. And propellers are more efficient than waterjets at low speed. The force generated from the sails depends on the wind speed at the sails. Wind at the sails is a combination of the ambient wind (true wind) and the forward speed of the boat. We call this combination the apparent wind. And at low speeds, propelling the boat forward increased the apparent wind, even if the true wind remains the same. More apparent wind = more force from the sails.
It depends on the ship speed. Below 20 knots of speed, pod drives and props are generally more efficient. Above 30 knots, waterjets are generally more efficient. Between 20 - 30 knots, it goes case by case.
Couldn't a screw in a tunnel work like a water jet seems like one could put thrust ports along the tube to help with maneuvering and how much water actually enters.
just use both; or like I mentioned in another video put the propellers up front not in back, yeap. Hve a channel effect so propeller has just the right amount of air to water to work in ht/room. As the channel gets smaller the inline props get smaller still just the right amount of water & air in the tube, then it gets down to jet size & they get their chance & steer w/them out rear in directions u want or multi directions u want at same time.
With the proliferation of small electric drives, would it be possible to have both propeller and a waterjet for the different speeds? Below 20, lower the prop. Above 20, lift up the prop and fire up the waterjet?
Yes, it is possible. Although, depending on the complexity of the installation, it may be more cost effective to just use the electric drives and the waterjets, with an adjustable inlet. Adjustable inlets on waterjets are rare, but they do happen. Usually on military craft.
@@DatawaveMarineSolutions So you're saying it has a variable ratio jet? Increasing the ratio at lower speeds let you ramp up the efficiency sooner on the curve? Sounds similar to fighter jets which tighten and open up the tail to fine-tune the exhaust.
DMS sólo proporciona ingeniería y diseño. Para comprar una turbina, vaya a www.hamiltonjet.com/ o www.kongsberg.com/maritime/products/propulsors-and-propulsion-systems/waterjets/
Hi there. Are the pump jets used in submarines considered water jets or are they more like ducted propellers:i.e. they minimize velocity change like a normal propeller.
I would call them closer to ducted propellers, assuming that they are optimized for slow speed propulsion. But I can't say for certain, since I don't have the design data for those propellers. And I doubt any navy wants to hand over the data to their highly classified submarine propulsion systems.
Am I correct in presuming that drag boats use prop systems due to the heavy load they are placed under?
Another great video!!!
It is partially the load and partially the extreme speed. But drag boats typically use surface piercing, super-cavitating propellers (also called surface drives), which are an entirely different beast from conventional propellers. The main goal of surface drives is to minimize the area of propeller in the water, because at those speeds, the propeller produces significant drag in the water. With a surface drive, typically only the bottom half of the propeller is in the water.
Much quicker out of the hole.
Very little "slippage" , whereas pumps need to get "spun-up" to reach their efficiency.
Datawave Marine Solutions really interesting, I was about to ask about surface drives, are they more efficient than water jets at high speed?
@@DatawaveMarineSolutions l
Invented by Hamilton, he would blast up mountain river systems white water rapids etc their ideal in those conditions.
Every time I have an obscure marine engineering question, DMS Marine pops up with the correct answer. I love it. The details on velocity ratio and relative application speed where right on target for me. It makes sense from a fluid dynamics perspective, but sometimes when you just have boat lust, you forget the basics. A little like those new toroidal props the kids are making for drones. There are certain advantages, but a much smaller optimized operating range.
sorry, I nattering.
Thanks for an awesome set of videos. It's a lot of work and they continue to amaze.
You forgot the jet benifit in brown water/ultra shallow applications.
What I really like in water jet it doesn't need gearbox for reverse
When I watch your videos I have no idea what decade I am in. I guess in a way it makes your information even more timeless. Thanks for the great content and details.
It was 2019 when you wrote the comment. It’s 2020 now. You’re welcome.
@@dylconnaway9976 📆😁
1968, patrol boat river. My first contact with jet drives. Twin v-6 Detroit diesels, Jacuzzi jet pumps. As I recall. 32 feet long, the jets made us think we knew what we were doing. Easy to maneuver in tight quarters, also in wind and current. Swore I would have one when I got back to the world. Then I found out what they cost, back to oars.
I just got back from key West Florida and in the shallow Waters I saw many carved lines in the coral created by boat propellers. I guess the jet propulsion also has an advantage there.
Jets are also safer for sea life. No prop, no badly scarred manatees.
Thank you, this addressed the questions I had without me needing to wade through the advertising hype. I've been enjoying your channel. Have a great day.
It has been a great use of my time watching your video,
I love the way you explained keeping it simple.
Just wanted to comment, I have read (actually You tubeing) and it seems that there is an alternative to the gray area of 20-30 knots regarding efficiency (I do not think for maneuverability). The so called Advanced Propellers by
Maarten MOSTERT that claims the fuel reduction by increasing propeller efficiency up to 20%.
The other is the Voith Linear Jet, they states that has better efficiency than water jets up to 40 knots.
Both above options with simple maintenance as a conventional propeller (who has waterjets know about its maintenance, specially when marine life give a pain in the neck.
I may say it is worth to compare all three systems in the 20-30 knots.
Thanks and keep the excellent work
I agree. I knew about the Voith linear jet, but the Advanced propellers were new to me. Thanks for the information!
advancedpropellers.com/
Eventually, I hope to make a video discussing the options in the transition region.
Coulod you do an analysis of the Volvo forward facing counter rotating props in the yacht world?? That would be very interesting.
Jets can also operate in very shallow water
as long as there are not a lot of leaves on the bottom, for the jet to vacuum up. saw that on a jet powered kayak. guy was in shallow slow moving creek, kept having to stop amd clean out the intake svreens. yes i like jets better in the shallows or arpund stumps, dont forget to pull the locking pin on your outboard so they motor cam come out of the water when it hits something...
Nothing is really good in very shallow water. Jets suck up stones, sticks, sea weed, and all kinds of things that can damage them. That's easier than you think, shells are nasty on the impeller, chipping the shit out of everything. They do go slightly shallower, but not much. Fast application is a little different, but still, not that much if preservation is your goal.
Hi, I am new in this excelent canal, very ilustrative! My question is the following: I have in mind to use a fast boat with a capacity of 20 passengers and I would like to understand what type of water jet pump should I use and what engine? I have in mind a super charged diesel engine, preferably due to the basically cost of fuel here in Peru.
I need recommendations to have a better understanding of engine ratio, weight, speed.
The intention is to take visitors through the rivers of the Peruvian jungle at relatively more efficient speeds than outboards and basically thinking about shallow rivers where outboards are inefficient.
thanks for your comments......
You mentioned the waterjet has a lower intake than the vessal and from what i understand this is what hinders it from being able to produce the proper thrust at lower speeds... What if the inlet for the jet was mounted on the sides of the vessel but still below the water line to insure no air entered the jet when at full speed? Or maybe installing ram scoops to help pull the water in as you pick up speed so you could start out slow but as you move the scoops help pull in more water amd increase the efficiency? Just a thought.. :)
Surface drives is what I'd be interested in! Yachts like Pershings seem to have amazing efficiency at very high speeds
They have jet drives, don't they?
@@KKhhoorrnniittee No, only a few of their models, possibly only one right now. I mean from Pershing 6x to 9x they use surface drives and thanks to that they're so fast they could get from Odessa to Snake Island in no time! I think right now The 140 is the only one with jet drives, making it a lot faster than huge ships like the Moskva...but then again all boats are faster than Moskva since it's in the bottom of the Black Sea along with a pretty good number of orcs.
@@pistonburner6448 Is that one of the terrorist ships that were sunk at Pearl Harbour?
I wish to undertake a logo design for DMS...I love the info presented...but I wish the logo graphics were much better.
This is a great video. Very informative, short and to the point. Thank you!
would love to see a video comparing Arneson surface drive to jet pump.
Very interesting subject matter and thanks for sharing your experties. Nice presentation!
I dont have anything to do with ships. Love this channel though, its very....relaxing.
I´m old fashioned. I favorite the good old sidemount paddle wheels, those where only the blades submerges in the water :)
I really like this information in my new project, thank you very much, God bless.
There is a local river where I live that goes from 20+ ft deep to 6 inches deep all along its length. Its nothing but a series of pools and shallows with a gravel sand bottom. Jet boats are the only type of powered boat that can be used on it. Most people have a wide shallow draft flat bottom boat with a outboard jet.
Should add discussion on cavitation. Waterjets operate best under laminar flow. If too fast and there is excessive air, they don't work, as thrust is reduced. Same with Propellers. The speed limit for a blade going through water is around 50 to 55kts where cavitation occurs. Once you hit cavitation speeds, you lose thrust over any propeller or impeller. This includes obstructions from badly designed brackets and hull designs. Water jets do not work with stepped hulls, where the step adds air under the hull that can get ingested into the water jet.
One problem not mentioned sea weed , floating grass caught up on the intake grates needing to be cleaned often . Perhaps they have an auto system that cleans the intakes .
Nets and ropes usually dont tangle, but do on props. So you win and lose.
Its called maintance
Really enjoy his unabashed nerdiness.
Your videos are really informative & helpful. Thank you.
great subject. I would like to see a comparison in navegability/speed/stability of a 35 ft catamaran versus a 40 or above for ocean crossing.
Great question. Unfortunately, too complicated for a simple TH-cam video. That would require a detailed trade-off study. Let me know if you ever want to contract DMS for that work.
What would use more fuel? Crossing the Atlantic at 14 knots with a conventional propeller, or crossing it at 30-35 knots with a waterjet? That would be a huge deciding factor I would think.
Slow is definitely more efficient. Not to mention it's very unlikely in an Atlantic crossing to have conditions suitable for 30-35 kts. Even in a big yacht you're forced to go slower due to sea state more often than you'd realize.
Would love to hear your opinion on a propulsion system mimicking a manta ray's wings.
The analogy to aircraft of turboprops vs. turbo fans is inescapable.
I agree, although planes try to minimize the speed to increase the efficiency (more flow less speed), and here they apparently find efficiency at higher speeds.
I wouldn't say minimising the speed of an aircraft optimises efficiency.
After all, in most applications your efficiency is in terms of fuel used for distance travelled, and the design of an airframe and engine combination has a distinct point of maximum efficiency at which both faster and slower speeds are worse.
Plus, props, turboprops and turbofans all have other constraints.
A turbofan is more efficient in lower density air, thus it encourages flying at higher altitudes. Indeed it's not usually very effective flying below 30,000 feet with any kind of jet engine.
conventional props meanwhile, lose power with altitude to the point that you likely wouldn't even be able to get most of them up to 30,000 feet...
For most low speed applications a prop is likely more efficient, but it also has more mechanical wear and tear, and it's difficult to achieve high speeds without a very large and heavy engine.
In aircraft there is of course a major transition point - supersonic airflow; Once the airflow goes supersonic, the physics change.
This means you either want something to be entirely supersonic, or not at all. When parts of a system are moving through air at supersonic speeds but not others, bad things tend to happen.
This is one of the limitations on prop aircraft, but it's also why a turbofan is more efficient when it spins slower;
It's not because you're trying to make it slower in general, it's that you want the fan diameter to be as large as possible without the fan tips hitting supersonic speeds.
The core of a turbine however, operates best at high speed.
This means there's a tradeoff between the speed of the turbine, and the speed of the bypass fan.
Since in most designs these are directly coupled, the faster the turbine, the more power the engine produces, but because the bypass fan produces most of the thrust, the bigger the fan the better... Until the fan tips reach supersonic speeds, at which point you either have to slow down the turbine, or use a gear box, which adds weight and complexity...
Hi, What motor would you suggest using on a 5 seat inflatable boat?
Sorry, but an exact motor sizing is considered contracted work. I recommend you look at some Zodiac boats (www.zodiac-nautic.com) to see what motor size they use on a comparable boat. Compare the boats based on length and beam, rather than seating capacity.
thanks so much for your sharing ,it is a very clear and sound presentation
recall a 18' jet boat with 10 people onboard that had lots of engine noise but not enough thrust to put it on plane. Very embarrassing for the owner. He finally resorted to just puttering around the harbor.
TEN ppl on 18'? Problem may not have been simply lack of power.
Whaaao! Perfect channel for relaxing satisfaction of my curious mind
Thanks with this. Inam drsigning a swoth trawler and was curious about this.
What do think of pumpjets as used on submarines and are now available for yachts/commercial shipping. Voith in Germany now offers them and I wonder if they are a good comprise if draught is an issue.
I have aspirations to build a folding trimaran but I really hate that most have an outboard hanging of the transom - really spoils the aesthetic not to mention can't help with the weight balance. Seems straightforward to me to have a small jet drive with a motor placed more centrally. They can sail at 20 knots so maybe not too much of a dent in efficiency and anyway would be sailing most the time.
Just wanted to say I enjoy your videos!
I could care less about efficiencies simply because I like the outside of my boat to be smooth without something hanging down that can get caught on things and possibly damage wildlife or get damaged itself or in the case of running aground, acting like an anchor.
We had a couple of WJ boats back in the 1970's. Both were 21 foot, both Ford 351, the workboat carried heavy loads and had a single stage 10 inch jet, the other boat was more pleasure and used a 3 stage 6 inch jet, both made by Hamilton Jets here in NZ. The 3 stage was faster, but the 10 inch single had the least speed change when loaded.
I'm wondering ,is the factory for Hamilton jet next to Rotorua where the sulphur spring baths are?
This is very helpful. Thank you
Good video . Question : should large hospital-ships not be installed with waterjets ? Wouldn't fast deployment and mobility not be a plus for changing global and distant geografical use when quickly needed in situations of emergency at big disasters ? Would also the combination of waterjet-propulsion and hydrofoil-hull not result in the fastest possible distant deployment for a hospital-ship ? Are such vessels already being built and thought of in terms of design ?
Yes, fast deployment would be a major advantage for hospital ships. Waterjets are one way to achieve that. The hydrofoil hull could create faster deployment, but there are other factors to consider. What you described is a ship that can respond to disaster scenarios. In addition to being a hospital ship, it also needs to provide logistics support to a disaster region. Flying in food, tent shelters, supplying fresh water, supporting helicopters to carry wounded back to the hospital. All that adds up to a lot of weight, and hydrofoils are not good at carrying large amounts of weight.
Further, hydrofoils add a lot of draft, which would restrict the ship to only enter deep water ports. A flexible disaster response needs to be more like the Wasp-class amphibious assault ship: able to deploy anywhere you have a beach.
To my knowledge, no one has plans to build such a vessel. This would be an expensive ship. And you can only justify that expense if the vessel sees use 80% of the year. Disasters don't strike that often.
Hoping this question wasn’t already asked or is plainly obvious: When you say ‘velocity’, I believe you mean the velocity of the boat, not the water that is jetted out. For your example of the large barge, with a smaller jet at high RPM, the water exiting the jet may be 30+ knots (limiting factor being cavitation along with impeller efficiency), while providing modest thrust for the large mass thus the barge may travel at say 5 knots. My question is, am I right to conclude that the efficiency is related to the velocity of the jet, not the boat itself?
Jet efficiency depends on a host of design factors. But if we ignore all the other design factors and just focus on speed, efficiency generally goes up with water velocity at the inlet of the jet. When a boat has forward speed, that forward speed helps to supply much of the velocity at the inlet. So technically, jet efficiency is tied to velocity at the inlet. But inlet velocity is also tied to forward speed of the ship.
1:24 - I would love to get information about the physics behind utilizing change in pressure versus change in velocity to generate thrust.
Thanks for the video
Great video! 👍 I dig it, all things jet boats is our deal at Jet Boat Mayhem 🚢 😎 👌
I want one sounds like fun ,, good video
I find it interesting, you talk about DMS in the 3rd person, yet Nick you are DMS, according to your website you are the only staff member, so drop the 3rd person and talk about your company as it is yourself and no one else.
By far the Biggest reason i bought a water Jet driven boat was Safety, B4 they had the safety strap on outboards didn't see this thank God but heard of this accident involving the death of two innocent kids when a bloke hit a wave was thrown overboard as his boat was racing out of control, after that i knew i would never again have a prop driven boat and as you rightly said the boat jet combination has to be right had a 14. 6 inches dateline with a V6 driving a PP6 jet unit combination was not the best as the boat would struggle to get on the plane facing the sky engine screaming doing 12 knots then once on the plane same RPM would do about 28 -30 knots topping up at just over 40 the other was about 17 food same engine very well marinized by Castolti jets Milan Italy driving a 09 jet the jet unit had a reduction gearbox build into it to suit any engine of your choice getting on the plane was totally effortless the PP6 jet was definitely better at high speed maneuvering but its impeller size was too small, it also had no build in gearbox n at times was wasting engine torque, same time it was a Lot cheaper to buy so overall both gave good value for money, speed boats are usually used for water skiing n fast fun boating so for me on all the issues water pumps are my choice too good video thx
Aggree
I see these "performance" boats with five or even six outboard engines, can these five or six props really get enough water to realize potential or is this just to look good?
Sir is water jet also good for big waves??
Or are they good at open sea??
Great question I haven’t seen an answer anywhere for this.
I'm thinking the same. What happens to the whole system in a rough see if the inlet is lifted clear of the waterline and it sucks in air? Presumably it'll unload and overspeed and need some sort of control to manage it.
So my idea of mounting a jet engine backwards on the deck pointing the output at my sails is still safe.
Very interesting!
Rất hay với mô hình trong cuộc sống
This is a trimarand question. Why are the outer hulls always higher than the center hull, it makes the boat rock/handle like mono hull. I plan to build a trimarand where all hulls are equally in the water and supporting the boat.
It depends on the purpose of the trimaran. For what you described, those trimarans are trying to optimize for speed. Placing the outer amas higher does two things:
1. Reduces the draft of the outer amas and reduces their resistance to help the boat go faster.
2. Placing the amas higher means they provide buoyancy over a larger range of heel angles before becoming fully submerged (the point when things get bad for a trimaran).
Other trimarans do exactly what you are suggesting. More important than the draft of the amas is their relative displacement and waterplane area compared to the center hull. Larger amas make for a stiffer / more stable ride.
Great video. Thank you.
the only disadvantages of jet propulsion are the cost and complexity of the project, which increases maintenance costs.
Can you please do a video on the thunder child 2 hull? If you can't do a video specifically on it could you please do one on some of the technologies it uses. It is an extremely visual striking design that also seems to be very good at what it is meant to do.
Frank Kowalski, the father of that hull, described it as an asymmetrical catamaran (being such in the stern and tapering off to single hull in the bow) with a foil in the aft (between the catamaran halves) to promote planing. Oh, looks like we have a hybrid of two hybrids there {scratches head in confusion}. Definitely worth hearing a professional's opinion from a scientific standpoint.
Have anyone tested a combination of water jet propulsion and propellers? For example waterjet engine in the middle and two IPS engines on each side? You could program the waterjet to turn off between 8-25 knots for efficiancy
How do you crab or walk the boat sideways such as in docking? What position do the buckets need to be and what RPM?
You can see a demo here with hamilton waterjets:
th-cam.com/video/RryL3XwUO50/w-d-xo.html
Crab walk only works with two or more waterjets. The buckets need to be set with one jet providing forward thrust, and one providing reverse thrust. Set your waterjets at opposite helm angles. Then the forward and aft thrust cancels out. Net result: sideways thrust.
Practical example: say you want to crab to starboard.
1. Set the starboard jet for forward thrust, jet angled port. (The physical jet on your stern. The bucket swings toward the port side.)
2. Set the port jet for reverse thrust, jet angled to starboard.
3. If you carefully balance the buckets, the boat crab walks to starboard.
This will probably require a high RPM, because most of the waterjet power cancels out. It's only a small component that gets directed sideways. I would definitely practice in away from the dock the first time you try this.
**Many boats have linked steering. You can't individually control the jet directions. In this case, still use the opposite jet thrust. It still works, but not very well.
Maybe it might be wise to have both propellor and water jet. Then you can switch between the two depending on application.
I have a 1979 glastron carson, I'm looking to change it to a twin water jet system with jetski motors. The question is who sells the kits on water jets.
Thanks to Bill Hamilton of New Zealand.
My question relates to the efficiency of the water jet. I only know what I saw watching your TH-cam video about water jet propulsion systems. Your claim of 90% efficiency sounds great and should help with using the water jet on a solar fuelled boat. I am thinking that an efficient electric motor could turn the pump. Do you have any experience in this area? I am in the brainstorming step on picking a propulsion system that I hope could be run by solar and a backup generator if the sun is not out on a 30 foot catamaran. I would be replacing an inboard Volvo 220 engine. I am hoping with the more efficient batteries and motors I can find a really efficient propulsion system. Otherwise stick to the same old technology the boat normally comes in.
The 90% efficiency only relates to the pump, not the waterjet as a whole. The waterjet as a whole will be around 40% - 55% efficient. At low speeds, the efficiency can drop down to 30%. The pump efficiency only measures how well the pump converts the energy of a spinning shaft into a pressure difference. The waterjet as a whole then converts that pressure difference into forward thrust.
I have done a fair amount of work on electric propulsion. I would not recommend a waterjet for electric propulsion. Waterjets are best suited for high speed, high power applications. Modern batteries are not ideal for high speed or high power.
@@DatawaveMarineSolutions Thank you for your quick response. Speed is not my goal other than say 20 to 25 knots when needed but long range efficiency using batteries capacitors and charged by generator, solar and 50AMP charging stations at the dock. So you reduced my options to stern drive and inboard outboard propulsion systems. Thank you. I really enjoy your videos. I would love to see one on converting stern drive engines say a Volvo 220 to an electric motor.
If the intake is adjustable would it help to get better efficiency
Are jets suitable for a sailing catamaran?
You can also consider the effect on wildlife. Driving a jet boat through spawning grounds of certain types of fish is like putting the eggs and fry through a blender. Drive through a mass of certain types of jellyfish and you can exponentially increase their population. The point is, consider the environment you'll be using each type of propulsion in, or your boat may last longer than where you intend to use it.
What about a propeller in a duct?
The advantage of a waterjet I'm looking for is the safety. A jetski could never be safe with an open prop.
But I would like to go slow. I'm thinking of more like a prop in a tube, I haven't seen designs like this, must be a reason..
Many large ships use a shrouded propeller. At higher speeds though, the shroud/duct becomes a large drag factor.
Another great video thanks. A question I've always been curious about is why don't Mono hulled sailboats have out riggers (not counting multi hull vessels). Is there any problems with retrofitting your own, like?
Because it would not help top speed, seakeeping, room aboard or much else. It would help righting moment, but all of the rigging and hull would have to be modified and strengthened, since there is no way for sudden gusts of wind to be unloaded from the boat by heeling, and it would not be able to go any faster with all of that extra power because would generally slam right into it hull speed anyways, just maybe a little quicker if that extra power could overcome the extra weight and appendage drag. It would be akin to training wheels on a bike. Help it stay upright, but extremely limiting everywhere else.
@@nicholaycalhoun1681 Thanks. I have a plan for refurbishing with the focus being to be as sea sound as possible. It's an interesting point about how the rigging in gusts that I hadn't thought about. Thanks again.
@@exploreseafaring Get a trimaran
Heel angle on a monohull sailboat is actually beneficial to the hull efficiency. The water line gets longer so the boat can go slightly faster before hitting hull speed and wetted surface area actually decreases up until about 20° of heel in modern designs which reduces drag.
@@otm646 Thanks. I've been waiting 2 years for this answer. Much appreciated.
THANKS FOR THE VIDEO
IS IT POSSIBLR FOR FISHING VESSEL OF 70 FT
Liked the video thanks for the education, new sub here .
I have a question to ask you , I work for a company that services boats . The agency who owns a boat that has twin Volvo diesels can’t stand the 46 ft v bottom that just nearly won’t plane . I think top speed is about 21 kts. They can’t see over the bow it’s bad. Twin jets , I believe they are hameltons . Do you have a clue where I can start? It’s a shame to see it sit and not get used .
Sounds like boat is trimming to far aft to get past its hump speed. I would try adding some interceptors on the transom. (Assuming you have any room between the jets.) Other tricks: look for objects on the boat that you can move forward (furniture, spare equipment, people, etc.).
If that doesn't work, DMS offers professional engineering services. For the right price, I would be happy to look into the issues with that boat. You can contact me at sales@dmsonline.us Hopefully some simple adjustments are all that you need. Good luck.
Why can't you put water jets more under water? Aren't the rooster tails a sign of inefficiency? What if you mounted them at a 10 degree down angle to push against hard water? Wouldn't that make them more efficient?
Thanks!
No physics stop them from going underwater. But they would be less efficient. Jets look inefficient because our brains are trained from looking at propellers. But waterjets work entirely different than propellers. They have their own set of rules.
That rooster tail is actually a sign that waterjets works like intended. We want a massive jet of high speed water out the back. It generates the momentum that pushes the boat forward. Without that rooster tail, we don't get the momentum.
Same way, if we put the jet underwater, the surrounding water would leach off the momentum of the jet, stealing our thrust. And if we mount at a 10 deg angle to push against hard water, it wouldn't do any good. We use the momentum of the water jet as it exits the bucket. Once the jet of water leaves the bucket, we gain no benefit from it. Pushing against the water can't help. The most efficient way to run a waterjet is straight, level, and just barely above the waterline.
@@DatawaveMarineSolutions This tracks. When Bill Hamilton invented the waterjet his prototype had a submerged nozzle. It did work, but it was very slow. Simply lifting the nozzle to be around 85% above the waterline provided massive speed gain.
Do you have the idea what is the working speed of water jet impellers? Say 20inch dia impellers?
Awesome video!
Thank you for explaining, when to use these different technologies.
I am curious if these water propusion theories also applies to small watercrafts, lets say a small one man ship or even rc boats big/small?
Afaik the physics should not change drastically.
-Regards a non native english speaker.
Yes, they apply at any size. But at smaller scale, it is easier to overcome inefficient propulsion with more power. So efficiency is less critical at smaller size.
So what's the difference between a propeller and impeller? Don't they both create a pressure difference to make thrust? The waterjet thing seems to me just a ducted propeller, but with a long duct (tube). Is it maybe like wind turbine blades where some are lift-type and others are drag-type?
Ducting a propeller increases efficiency and thrust. An impeller in a jet pump unit is effectively an optimised propeller for that application. It also uses stators etc to increase efficiency as stated in this video.
Thrust is created by the volume of water passing through the pump and exiting the nozzle. The nozzle is located at or slightly above the waterline to take advantage of the differential density of water vs air thereby giving the pump the ability to move larger quantities of water accellerating the boat. There is more to it when calculating speeds flow rate of the pump and exit nozzle diameter all play a part.
The jet pump has been around for some time but was not used so well until a NZ farmer by the name of Hamilton took the idea and moved the nozzle to the right location and created the first jet boat as we know today.
Both impellers and propellers do both create a pressure difference. But they exploit different ends of the pressure equation. For both a propeller and impeller, you get two changes in the water flow: a change in water pressure, and a change in water velocity.
A propeller tries to minimize the change in water velocity. It wants to only have a change in pressure, keeping all the pressure change happening right at the propeller blades. Any other changes are lost energy.
A waterjet uses a duct after the impeller. And that duct is crucial. It converts the generated velocity energy into back pressure against impeller blades, generating thrust. That means we can operate at higher speeds, generating lots of velocity change and still using that energy.
@@DatawaveMarineSolutions referring to a propeller as a screw would help explanation.
A water jet is a water pump on crack that moves massive amounts of water at high pressure. A prop pulls through the water like screw threads. Them old timers were pretty precise with nomanclature.
@@DatawaveMarineSolutions , great video, the main thing that I feel you may have overlooked with this kind of propulsion is the fact of how they operate in "skinny" water . this is a major concern in Alaska gillnet fisheries and 3-4 feet of additional draft with conventional screw propeller can make a huge difference , if you can see a seagull's knees you have enough water to travel and commercial fish with a waterjet, huge over looked value of this type of propulsion thanks Jeff
@@jeffkutz2118 Excellent point!
Ultra shallow areas for example 0,7m draft what kind of problem will be if the seabed is sand?
Why is a water jet not submerged?
I'd expect that output pushing against the water to be more efficient.
With the output above water you only get Newtons action-reaction force.
I have jet drives on my catamaran .With both engines running at full throttle i can get a little over 45 knots.
Observed myself, sea state 5, SAR 20 meter flaps shut down while on rescue. Had to be rescued herself.
Thanks for the content. Are the graphs from the video from [ J. Carlton, Marine Propellers and Propulsion, London: Butterworth-Heinemann Publications, 2007. ] ---> this source? If it is not, can you please inform me regarding that matter?
Thank you.
All references are listed in the video description. But the graphs I generated myself, based on equations provided in Carlton.
@@DatawaveMarineSolutions thank you for the reply, i will show your website in my references then.
Couldn't you put an openable venturi behind the water jet to increase it's low speed efficiency?
What about if it's under the water for low speeds propulsion say up to 12 knots, wouldn't this be better make it more efficient. I mean you've got the back force of the water behind the impeller nozzle to propel you would it help at low speeds if you made a nosey go from above the water to below the water at its optimum speed. And what about the impellers automatic adjusting of Pitch as well for the given circumstances speed thrust
I can't say with certainty. What you are asking requires some very intensive waterjet optimization, and those are the details that a waterjet manufacturer never releases. Most of these jets end up partially underwater at low speeds. Usually, the waterline rests right on the shaftline of the jet. But even if fully submerged, that may not improve efficiency. The jets have an impeller, followed by guide vanes, followed by a bucket. The guide vanes and bucket all add drag, decreasing the efficiency. We can afford drag penalty at high speeds. But at low speeds, the margins we don't have that much thrust to start with.
I also don't know of any impellers that allow automatic pitch adjustment. Most impellers are more like turbine blades. They are a single cast piece of metal, machined with high precision. They don't have any moving parts. You just attach them to the spinning shaft inside the waterjet. But that would be a neat feature if a waterjet included automatic pitch adjustment. Have you seen this on a specific model?
Take a look at Sir William Hamilton's performance figures for the first 2 water jets in a boat, both jets were used on the same boat, the boat was slow, the first jet discharged under water and the second above water, and it propelled the boat a twice the speed. You can test this by holding a reduced size nozzle water hose, then dip the nozzle under water, and see how the trust diminishes.
What if there were an auxiliary engine with a folding prop.
waterjet can use for surface modification?
How do jets do at pushing barges or towing heavy loads?
Has the "bucket" style thrust reverser ever been implemented in a power driven installation? Especially on a smaller pleasure vessel that thrust reverser method does not need to be bespoke.
Not that I have seen. Though I give it fair odds you can find a unique vessel somewhere that attempted what you described.
I have a video suggestion, cavitation plates
I do have a question although I not a potential customer.
Would water jets help a sailing yacht during low wind performance or during high waves in storm conditions ?
Thank you I am a curious person
Yes, they would. Although any propulsion device will help a sailing ship at those low speeds. And propellers are more efficient than waterjets at low speed.
The force generated from the sails depends on the wind speed at the sails. Wind at the sails is a combination of the ambient wind (true wind) and the forward speed of the boat. We call this combination the apparent wind. And at low speeds, propelling the boat forward increased the apparent wind, even if the true wind remains the same. More apparent wind = more force from the sails.
Hi, do you offer ship (Suezmax & VLCC) design and optimization consultation ?
Yes. For more details, send an email to sales@dmsonline.us. I will be happy to discuss the project details with you.
@@DatawaveMarineSolutions Where are you located and how much do you charge? - on project basis or hourly basis?
The pros and cons of waterjets and conventional propellers, but not.azipods... although I guess azipods are just a different setup for propellers?
Interesting .. not one word on variable pitch turbines or propellers currently in use on aircraft & some large ships .
That would be a good subject for another video.
Are water jets more efficient for distance over pod drives or props?
It depends on the ship speed. Below 20 knots of speed, pod drives and props are generally more efficient. Above 30 knots, waterjets are generally more efficient. Between 20 - 30 knots, it goes case by case.
Couldn't a screw in a tunnel work like a water jet seems like one could put thrust ports along the tube to help with maneuvering and how much water actually enters.
just use both; or like I mentioned in another video put the propellers up front not in back, yeap. Hve a channel effect so propeller has just the right amount of air to water to work in ht/room. As the channel gets smaller the inline props get smaller still just the right amount of water & air in the tube, then it gets down to jet size & they get their chance & steer w/them out rear in directions u want or multi directions u want at same time.
What about putting it on a house boat would that work out ok
With the proliferation of small electric drives, would it be possible to have both propeller and a waterjet for the different speeds? Below 20, lower the prop. Above 20, lift up the prop and fire up the waterjet?
Yes, it is possible. Although, depending on the complexity of the installation, it may be more cost effective to just use the electric drives and the waterjets, with an adjustable inlet. Adjustable inlets on waterjets are rare, but they do happen. Usually on military craft.
@@DatawaveMarineSolutions So you're saying it has a variable ratio jet? Increasing the ratio at lower speeds let you ramp up the efficiency sooner on the curve?
Sounds similar to fighter jets which tighten and open up the tail to fine-tune the exhaust.
What about debris getting sucked up into the intake?
Hola como hago para comunicarme quiero una turbina de esas
DMS sólo proporciona ingeniería y diseño. Para comprar una turbina, vaya a www.hamiltonjet.com/
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www.kongsberg.com/maritime/products/propulsors-and-propulsion-systems/waterjets/
Hi there. Are the pump jets used in submarines considered water jets or are they more like ducted propellers:i.e. they minimize velocity change like a normal propeller.
I would call them closer to ducted propellers, assuming that they are optimized for slow speed propulsion. But I can't say for certain, since I don't have the design data for those propellers. And I doubt any navy wants to hand over the data to their highly classified submarine propulsion systems.
@@DatawaveMarineSolutions thanks for the info👍