Hi.. My name is Edward from malaysia. Your video really makes me really understand how water jet works. Make more tutorial on water jet. I love jet boat. TQVM👍👍
I am no engineer but I'm great at logistics. That being said I enjoy watching your video. Between high school physics and my naval career I fully understand what saying or at least can figure it out. With that said I just liked and subscribed. Thanks.
Sir one more thing, can we add a variable nozzle at the outlet of waterjet like we have in fighter jet engine, I don't know the name of that thing but its use to increase and decrease the diameter of outlet which is very useful in some cases.
Hi, I want to design an efficient water jet pump for a diy surf board based on required static thrust. Do you have any recommendations on where to start from? Any books you can recommend? I know the basic theory but I need to understand how to approximate my design to get it in the ball park of what I want and then try to validate with CFD and experimental results. Also I want to estimate the required RPM and torque at full throttle that the pump requires.
Extra example for the first point you labour, Rockets don't push against the atmosphere, obviously because they work in space. It's the same principle you're trying to clarify. Following that, I know the lighter the molecule fired from the exhaust the better the performance of a rocket, same with air tools, lighter means faster tool (Helium wheel guns banned in F1). Would that principal mean deliberately cavitating the water to expand the air after the impeller, before the bucket improve thrust? ignoring for a moment whatever was cavitating the water would erode away (I presume nearly immediately).
In principle, I think so. the expansion from cavitation would result in greater acceleration of the water. But as you said, that would also erode away whatever generated the cavitation. But to address your point, that would essentially be an effort to inject expanding gas bubbles into the flow stream. Ships have experimented with compressed air injection for different purposes. Thankfully, compressed air does not suffer from the same erosion effects as cavitation.
If you were to design a nozzle that was capable of varying diameters, could you increase the efficiency of the water jet at various speeds? For example could a nozzle designed for a 35knot operating speed could be choked down in diameter at 25knot speeds to increase velocity and efficiency.
It seems like if you had an adjustable nozzle orifice on a waterjet , then you would also need to have either a way to change the the motors output @ X rpm or a way to adjust the impeller's blade pitch to match the needs of a changing nozzle size. And if you could do those two things then situations that required an adjustable nozzle size would be much rarer. Maybe
As always, a fascinating and complex subject made accessible and easy to comprehend! Thank you so much for what you do! With all the emerging technology around elegant electric motor designs and high performance batteries are there new realms where water jet design can be further optimized?
I'm not sure about further optimization. But I have seen new applications for waterjet design in recreational boating. Applications in kayaks, surfboards, wakeboards, scuba-propulsion, etc. Essentially applications of micro-waterjets. The interesting part is that the goal for those applications is to consider the trade-off between peak waterjet efficiency, and minimize weight of the waterjet. So you may consider removing some of the typical waterjet components like the bucket and the stators to reduce the weight. It reduces the efficiency of the jet, but improves the power / weight ratio or the overall device.
Sorry Nick The Naval Architect, I have to disagree with you. You said that water accelerated out the back of a boat equals forward thrust. That statement is not true unless you are in a vacuum and there is no resistance to the water exiting. Your rule #2, “the size of the rooster tail coming out the back, really doesn't matter,” is wrong. The following is a little story of how I know this: I grew up in a small town on a popular tourist lake. It was back in the 70's or early 80's and some jet boats had a power trim. They would sometimes drive along the beach lifting the rooster tail and shooting the water at least a hundred feet behind the boat. When they did that, they never had much speed and were only looking for attention from the girls on the beach. When trimmed properly, the boats were capable of much higher speeds just by keeping the water in the lake. One day though, a cabin along the beach caught fire and a guy with a jet boat saw the burning house. He backed his boat in near the shore, trimmed the boat to make a very large rooster tail and shot water at the cabin which was way up on the bank. While using his steering and trim to direct the water at the flames, he proceeded to put the fire out. The boat did not accelerate forward according to your second rule, it just inched along; in fact, he was able to apply full throttle with minimal movement of the boat and he put the fire out in under three minutes. Albeit, he had to back up a couple of times. The reason that the boat didn't go shooting across the lake was not because the water wasn't being accelerated (it was); it was because there was only a small build up of pressure behind the water jet when pushing it through the air as opposed to a large build up of pressure when pushing the water into more water. The size of the rooster tail out the back really DOES matter!
@@eduardodaquiljr9637 normally, no. You want the water jet outlet above waterline when running at speed. But if the pump is completely out of the water, it can't prime. (Prime = suck in the first water to get started.). Typical install: mount the water jet with the shaftline of the jet at the same level as the waterline.
Fantastic explanation.. But to help further my understanding... I expected the Action/ reaction and thrust component to need to react on water to provide thrust... Obviously the toy hoverboard did not have that... What is the other reasoning behind needing a nozzle to be low on the stern? My previous thinking was that the water stream reacted with the water for thrust.. But against air seems counter intuitive..? Any further help here? Thanks again. Casey.. ( trying to put together a mini jet boat out of PWC components..)
Well it really doesn't need to react on anything, if you think about a gun recoil it's pretty much the same principle. You have on one side your handgun providing a force to the bullet (action) and on the other the bullet providing force on your gun and by extension your hand (reaction), you will feel the same reaction independently of wether the bullet did hit the target or not. Same applies with this hoverboard here. As for the nozzle needing to be low I'm afraid I do not know either...
Lets say you needed a waterjet thruster rather than a propeller, for safety reasons, on a slow moving vessel (5kn). Would it still be necessary to have a nozzle to accelerate the water? Could not the acceleration take place in an axial flow impeller. Could it be, in this case, that a nozzle would converts high volume low speed to a lower volume with high speed and a potential loss in efficency. Another question: Judging from the shapes of waterjet turbineblades (not airfoils), are they so called supercavitation blades? Thanks for a amazingly clear and entertaining video.
To answer your question, yes you can absolutely place an axial flow impeller without a nozzle inside a tube for slow speed. Whether we would still call that a waterjet? I would say no, but it really is a debate of semantics and not about practical engineering. Even without the nozzle, the axial flow impeller will still accelerate the water. But if you are talking about protecting a propeller on a vessel moving at 5 knots, the more practical option is to just build a duct and cage around a conventional propeller, rather than build a bad waterjet. The propeller loses some efficiency due to the drag of the duct and cage, but it still does better than a bad waterjet. To your other question: No, waterjet impeller blades normally do not use supercavitation blades. We normally want to avoid cavitation within the waterjet. The blades look odd because they are designed to work with the spiral flow pattern of the water as it gets forced through the impeller while in a tube. But if you look at the cross section of the blades, they look like regular airfoil shapes.
Broadly, yes. The submarine equivalent is called a pumpjet. It's a little different to a waterjet. Waterjets are designed around operating on the water surface, with the jet outlet being above water, and the inlet on the bottom of the hull. Pumpjets pull water in from the front, on all sides. They are designed to operate underwater. And for submarines, the pumpjet tends to be most focused on silent operation rather than pure efficiency. I did a comparison video on this, which you can find here: ua-cam.com/video/Y8kJKL5M8ug/v-deo.htmlsi=l7sGMBXD4G_Va0VP And does a waterjet need a rudder? Usually, no. The waterjet usually has a bucket, which redirects the outlet stream. By changing the angle a little to the left or right, we can turn the boat. But pumpjets normally don't have a bucket, because it makes too much noise underwater. So submarines with pumpjets still use rudders.
Rooster tail doesn't matter in terms of thrust, true. However the angle of the rooster jet changes the trim angle of the boat which can increase planing efficiency (or make it worse!).
Your modern jet engine works on the same basic principle as a waterjet. The intent is that water exist the waterjet faster than it entered. The same is true for a jet engine: air exits faster than it entered. But how you achieve that goal works completely different in air at supersonic speeds. If you take a waterjet design and apply it straight in air at supersonic speeds, it will deliver exceptionally poor performance.
@@DatawaveMarineSolutions Thanks! I'm actually interested in a supersonic electric jet. And since propellers doesnt work well at those speeds, I'm looking for alternatives. But I guess a jet engine that only compress the air without the combustion process is a bit silly. Is there any way to make a supersonic electric jet at all? (assuming battery improvements obviously)
@@temporaryname8852 Excellent question. And, unfortunately, outside my field of expertise. I'm not sure how you would generate sufficient thrust. Fundamentally, the combustion process just imparts heat to the air, causing expansion. In theory, you could achieve the same effect with an electric arc across the air path. But it would take a LOT of a high voltage electricity.
@@temporaryname8852 I don't know if you're still interested, but an electric jet drive like you describe is fine in principle. The turbine in a jet engine isn't adding to the thrust. It consumes energy, so by removing the turbine, and driving the compressor mecanically, you get more thrust. A lot of supersonic planes already do this in a way. Even most fighter jets now have turbofan engines, where the core engine produces torque to drive the fan, which just shoves air through a nozzle without any fuel or heating to produce extra thrust. This is done for improved efficiency. In principle, you can get rid of the turbine and use an electric motor to drive a fan with a nozzle behind and you could even go supersonic with enough power on your motor. In practical terms it's fairly hopeless, because the electricity needs to come from heavy, bulky batteries. Battery powered planes are marginal even for slow prop planes. They get some use as trainers, since those don't have to fly far, but if you want to go faster, you need more power, which means range gets even shorter, to the point it would be useless for anything but a stunt. Batteries also have a maximum power output, so to power a supersonic jet, no matter how briefly, you'll still need a huge weight of batteries, which will make it difficult to fly in the first place. I think maybe an RC plane, or a very small manned one could maybe do it for a record setting run, but it just wouldn't be practical for any real uses.
My kyack with a human powered water jet needs the correct size nozzle ForThe 2 bilge pumpS I think I can pump 20 gals on each pump for a little while At 40 psi I think I need a 1/2 inch nozzle for each pump is that about rite.?
When I see that rooster tail and the acceleration, I worry about the suction power of waterjets. Do you have to install a grate to protect against fish getting sucked in...or people? But I know a conventional propeller also creates a lot of suction current and can be dangerous for people and fish too. Maybe you can make an addon video about what are the metrics of suction and how do you calculate how much is too much? PS, waterjets are cool, but icebreakers are cooler (literally). I hope you get to icebreakers soon.
You can see the grate on the intake in the video. But yes, you need something there. Small jet boats are notorious for sucking lines into their impellors, and it's a PITA to extract the mangled remains of the line from the system. Bigger jets normally means a bigger boat and bigger lines... and are probably even harder to untangle. Fish I suspect are less of an issue because they're bulky and easier to filter out, plus they're softer so they will tend to just pass through the jet and come out as a cloudy pool of water...
When a water jet driven boat speeds over a dense growth of water weeds or water not deep enough over a mud flat the water inlet becomes clogged and the boat stops. In the case of the now antique River Patrol boats as used in Nam fifty years ago the diesel driving the thing explodes as a connecting rod tries to leave the engine. This can be very exciting.
Are there any specific rules for designing the size of the jets inlet with respect to the nozzle diameter? I know the inlet velocity plays a big part but I'm trying to design a pump and need a decent starting size. Any help with be appreciated :)
Probably not, for two reasons. First, the RC jets can't afford the engineering cost to optimize a jet to the same degree as a commercial jet. Second, consider the weight of the electronics and motors to distribute that power to all the jets you would need. That would also reduce the overall system efficiency.
I had an interesting discussion with my friend. I claimed through what I learnt here that it does not matter where the water is pushed. But how come the jet is always pushed down to the water? Is it only to make the water jet not touch something else?
The physics will always work. You can place the pump 5 m above water level, and the basic physics of a waterjet still work. But the location of the waterjet does have a strong influence on the efficiency. It takes energy to pull the water above the static waterline. Quite a lot of energy, because waterjets need to do that with a huge flow rate. So a waterjet 5 m above waterline is much less efficient than a waterjet only 0.5 m above waterline. Sorry if the video mislead you. For brevity, I don't cover all the nuances of each subject. Otherwise, I need to recreate an entire college class.
Probably, yes. I don't normally do reaction videos or commentary on current events, because it can be too easy to jump to conclusions. But I am considering a video about the physics behind the grounding and the salvage operation.
@@DatawaveMarineSolutions Great: That's what I was thinking - there is a lot of questions around how ship dynamics precipitated that situation. Always enjoy your 'lessons'.
Does impeller generate pressure though, i think that impellers generates kinetic energy on the fluid which which increases the flow, by inducing kinetic energy its then transferred to more kinetic energy and less pressure in nozzle. Hope somone approves or agrees to my answer, because i know for sure that pressure in pump is a measure of the resistance not the impeller. Another question will surface roughness affect the performance of impeller?
I made an RC boat with a waterjet, and above a certain throttle point, the jet would completely lose all thrust. I believed this to be since the boat started to ride out of the water and the inlet wasn't, getting enough water to suck in by the pump. Does anybody have any suggestions, I'm sure this applies to real life.
Great question! I answer that in a separate video that specifically targets the questions of waterjet efficiency: ua-cam.com/video/fNNYUq5M-z4/v-deo.html
@@DatawaveMarineSolutions Ummm ... okay, so I have this incredibly stupid question of no real importance ... if I'm interested in "efficiency" in the sense of fuel economy, why should I *EVER* consider using a water jet over a prop (at least in the absence of having committed to having a big honking fuel hungry gas turbine as the ship's engine)? I mean, yes, F = m * a shows that you can get the same amount of force (thrust) from either accelerating a large mass a small amount OR accelerating a small mass a large amount ... *BUT* the kinetic energy of the accelerated mass is described by the equation KE = (1/2) * m * v * v and so small changes in v (which is the acceleration caused by said propulsive element be it a prop or an impeller) turns into very large changes in kinetic energy very quickly. And since that energy has to be delivered by the engine, and that energy comes from converting the chemical energy of the fuel into mechanical energy delivered to the propulsive element, that means that for a given energy input, acceleration a small mass by a large amount is always less "efficient" in the fuel economy sense of the word than accelerating a large mass by a small amount. So in the case of air instead of water, a quad copter with relatively small diameter props is almost a stupid idea compared to a helicopter with a single larger diameter prop, at least when it comes to "efficiency" as in getting the most lift for the amount of energy in your batteries or fuel. So what am I missing here? Why can't I beat the crap out out of any water jet in terms of fuel efficiency by just making the prop or props larger in diameter? Is it that you can only go so large in increasing prop diameter in water before cavitation sets in? And if cavitation is the culprit, then why isn't this justification for using a prop that doesn't move in a circle like a lifting vane configuration?
@@lewiscole5193 In your logic, one major factor to include is that the efficiency of a waterjet / prop is not uniform across all speeds. In general, you are correct that a large diameter propeller beats a smaller propeller in efficiency. And at lower speeds, a propeller beats a waterjet in efficiency. But at higher speeds, the efficiency of the propeller drops off and the waterjet efficiency improves. Eventually, the waterjet becomes more efficient than the propeller, at high speeds.
@@DatawaveMarineSolutions Thank you for your response. At the outset, let me say that I'm not a naval architect and I don't play one on TV. What I am is someone who has been interested in aircraft forever and who once upon a time thought about designing and building one of my one. So I have a basic familiarity with aerodynamics and aircraft history and what I'm curious about is why something that applies to aircraft doesn't seem to apply to ships rather than to start an argument. So back to your response. I think, we are talking at cross purposes here as I'm *NOT* talking about "efficiency" as it's usually defined, namely the ratio of power out (usually denoted by eta[o]) to power in (usually denoted by eta[i]). Instead, I'm referring to "efficiency" in the sense of "fuel economy", and in this case, both Newton's Second Law and the definition of kinetic energy don't give a damn about "efficiency" at some particular speed or even over a range of speed. Both equations together indicate that it is *ALWAYS* more "efficient" in terms of minimizing the amount of energy you have to deliver to the propulsor element to get a given thrust by accelerating a larger mass to a smaller speed than to accelerate a smaller mass to a higher speed. In short, a larger prop *ALWAYS* wins out over a smaller prop (or jet impeller) for any acceleration (which is what "v" in the equation for kinetic energy really is) independent of propulsor efficiency at some particular speed or speed range. In the case of aircraft, a prop powered aircraft always wins out over a jet powered aircraft so long as the jet's fan is of a smaller diameter absent some other consideration(s). Even today, virtually all smaller air liners are always prop driven even though they used turboprop engines rather than Otto cycle engines. And in the case of larger airliners, large "props" still win out as that's what the fan at the front of a high bypass turbofan engine really is (albeit a prop in a duct) compared to low bypass turbofans or pure turbojets. Even larger "unducted fans" are better still where such props have a scimitar shaped blades to reduce losses from shockwaves on their surface. It is not efficiency (or the lack there of) that has prevented these "unducted fans" from appearing in anything other than test aircraft, but rather noise. So, getting back to the issue at hand. Even if a jet of some diameter is more "efficient" at a given speed than an identical size prop, I should always be able to beat the jet simply by increasing the diameter of the prop OR increasing the number of props absent some other consideration(s). And whatever the "efficiency" of a water jet might be at some "higher speed", it would seem to me that a larger prop should still be an option ... after all, as far as I know, all of the non-gas turbine powered hydroplanes are powered by props rather than water jets which I would assume would not be the case if a jet's efficiency advantage at higher speeds were overwhelming compelling. That gets me back to lifting fans. Once upon a time, Lockheed proposed their "sternwheeler" jet transport called the Omega which used lifting fans rather than either props or jets for propulsion. Not having to move each of the lifting blades in a circle where one end was fixed at the axis presumably should have reduced/eliminated compressibility as an issue for said propulsor. And if cavitation is what limits prop diameter on a ship (is it?), then a lifting fan should be able to move more water without cavitation getting in the way. In the case of the Omega, presumably the expense of getting an airworthiness certificate got in the way of its lack of further development, but no such constraint presumably exists for a ship and so I'm left wondering why I haven't seen even a proposal for a lifting fan powered ship. So can you please wave your arms at the discrepancy again as it does *NOT* seem that "efficiency" at higher speeds is a particularly good answer to my question(s)?
@Lewis 1. The way to maximize fuel efficiency in any engine is to switch it off. 2. If motorbike can get 80 mpg. Why would anyone drive a car, or lorry? 3. You say a bigger prop is better, but you seem to forget it's also bigger, ie heavier, and needs a heavier thing to hold it and a heavier thing to turn it. You can't strap an A300 Airbus engine to a little Cessna - it'd collapse.
Probably not. The stern shape of the ss United States would make it very difficult to fit in a waterjet. Technically, it is possible. But it would probably be a waste of effort.
I have a stupid question. Lets say i was doing a restomod of a 1957 chris craft. I wanted to take the jet pump from a jet ski but have it ran by the 131 hp engine. would the jet even work given lower rpms of the larger motor?
Not a stupid question. Unfortunately, too complicated to answer without detailed knowledge of the jet, hull, and the motor. But you are correct to consider the problem of lower RPM from the motor.
The best way to test all of these theories is to make it out of pvc. If you can make something half as large out of pvc then you can figure out nozzle size and intake shape and so on
If you would like a confidential discussion, you can contact me at sales@dmsonline.us. I can prepare an NDA to protect any confidential information you share.
Depends on the bucket design .. and of course how deep the harbor/marina is. Some buckets direct the jet straight down in neutral, other direct it only slightly down but mainly to the sides .. the ones that shoot straight down could definitely disturb the floor or worse a reef ..
Technically, yes. But there are other options that are more efficient for a tug. Options include conventional propeller, controllable pitch propeller, azipod, or Voith propeller.
Sadly, Google translate did not do this justice. Sorry, I do not speak Mandarin / Chinese characters. From Google translate, I understand the basics. 1. Impeller pressure relates to efficiency. 2. Inlet of impeller, minimum limit is vacuum pressure. Agreed. 3. Cavitation of impeller. Something about surface effects. I wish I spoke the language.
@@DatawaveMarineSolutions "1. First impeller won't have too high of an exit pressure, or the efficiency goes down. 2. The limit of the pressure at the inlet is vacuum. 3. The diameter and RPM of the impeller is ultimately constrained by cavitation. China has production, but the quality is basic. I have switched to the research of surface drives" Might have made some mistakes, not specifically my field of study.
With potential for 90% efficiency I am thinking a matched design of electric motor and water jet (vs propeller) on a blue water sailing yacht, say a NEEL 45 or 47 trimaran, or similar catamaran (light weight, low drag) might make electric powered propulsion viable. Solar, wind, and water electric generators for ongoing recharge. Add an appropriately sized genset for backup.
You have to be careful. The PUMP is 90% efficient. The waterjet as a whole is around 40 - 60% efficient, depending on the model you select and how you use it. Remember that the pump only generates pressure. The rest of the waterjet still needs to convert that pressure into thrust, which involves some additional efficiency losses.
Not a great shape for water jet impeller at around 7:00. Most important to add ... gap between impeller and the water jet wall or pipe is SUPER CRITICAL. The gap has to be really small. Stator is NOT optional.
So a waterjet is actually more like a rocket, as in the propulsion comes from it shoving a load of mass out of the back, ergo it would work in space (if it had a water source)?
@@sepg5084 No because a jet in part gets it thrust by pushing against the existing atmosphere and causing an overpressure. Whereas a rocket relies solely on the expulsion of mass at high velocity.
Dear friend make a video explain "SEA GOING AND RIVER VESSEL".... very few info online; just broker advices... i think very few people know, most of the little info online is from North Europe and former USSR countries. flat advices from design bureau of Germany, Sweden, Netherlands, ... nothing really clear and good explain.
As a general rule, DMS doesn't include the mathematics in the presentations because several of the engineering concepts can be implemented incorrectly when taken take out of the larger context of a full education in ship design. If you are interested in the mathematics, the video description lists several references used to create the presentation. Reference [2] would be a good starting place.
Hi, I'd like to build a water jet that operates BELOW water. Like this one aerofoils.de/ You say that the efficiency drops off - can I simply enlarge the nozzle to reduce the hydraulic locking effect below water? Or just operate with no nozzle effect at all turning it into a ducted impeller?
Hi.. My name is Edward from malaysia. Your video really makes me really understand how water jet works. Make more tutorial on water jet. I love jet boat. TQVM👍👍
I am no engineer but I'm great at logistics. That being said I enjoy watching your video. Between high school physics and my naval career I fully understand what saying or at least can figure it out. With that said I just liked and subscribed. Thanks.
The maneuverability simulation at 13:15 is really cool!!!
I agree, especially with the motors at 3/4 throttle..
Do you have any formulas to help calculate the sizes? ie: inlet, to pump diameter to nozzle? Thx Mike
Sir one more thing, can we add a variable nozzle at the outlet of waterjet like we have in fighter jet engine, I don't know the name of that thing but its use to increase and decrease the diameter of outlet which is very useful in some cases.
Hi, I want to design an efficient water jet pump for a diy surf board based on required static thrust. Do you have any recommendations on where to start from? Any books you can recommend? I know the basic theory but I need to understand how to approximate my design to get it in the ball park of what I want and then try to validate with CFD and experimental results. Also I want to estimate the required RPM and torque at full throttle that the pump requires.
perfect explanation thx a lot!!!
Extra example for the first point you labour, Rockets don't push against the atmosphere, obviously because they work in space. It's the same principle you're trying to clarify. Following that, I know the lighter the molecule fired from the exhaust the better the performance of a rocket, same with air tools, lighter means faster tool (Helium wheel guns banned in F1). Would that principal mean deliberately cavitating the water to expand the air after the impeller, before the bucket improve thrust? ignoring for a moment whatever was cavitating the water would erode away (I presume nearly immediately).
In principle, I think so. the expansion from cavitation would result in greater acceleration of the water. But as you said, that would also erode away whatever generated the cavitation. But to address your point, that would essentially be an effort to inject expanding gas bubbles into the flow stream. Ships have experimented with compressed air injection for different purposes. Thankfully, compressed air does not suffer from the same erosion effects as cavitation.
If you were to design a nozzle that was capable of varying diameters, could you increase the efficiency of the water jet at various speeds? For example could a nozzle designed for a 35knot operating speed could be choked down in diameter at 25knot speeds to increase velocity and efficiency.
Very interesting, I don't know enough about the topic :)
Since water density doesn't change i don't think it will be useful.
It seems like if you had an adjustable nozzle orifice on a waterjet , then you would also need to have either a way to change the the motors output @ X rpm or a way to adjust the impeller's blade pitch to match the needs of a changing nozzle size. And if you could do those two things then situations that required an adjustable nozzle size would be much rarer. Maybe
As always, a fascinating and complex subject made accessible and easy to comprehend! Thank you so much for what you do!
With all the emerging technology around elegant electric motor designs and high performance batteries are there new realms where water jet design can be further optimized?
I'm not sure about further optimization. But I have seen new applications for waterjet design in recreational boating. Applications in kayaks, surfboards, wakeboards, scuba-propulsion, etc. Essentially applications of micro-waterjets. The interesting part is that the goal for those applications is to consider the trade-off between peak waterjet efficiency, and minimize weight of the waterjet. So you may consider removing some of the typical waterjet components like the bucket and the stators to reduce the weight. It reduces the efficiency of the jet, but improves the power / weight ratio or the overall device.
Can you please make a video on the water jet cavitation
Sorry Nick The Naval Architect, I have to disagree with you. You said that water accelerated out the back of a boat equals forward thrust. That statement is not true unless you are in a vacuum and there is no resistance to the water exiting. Your rule #2, “the size of the rooster tail coming out the back, really doesn't matter,” is wrong. The following is a little story of how I know this: I grew up in a small town on a popular tourist lake. It was back in the 70's or early 80's and some jet boats had a power trim. They would sometimes drive along the beach lifting the rooster tail and shooting the water at least a hundred feet behind the boat. When they did that, they never had much speed and were only looking for attention from the girls on the beach. When trimmed properly, the boats were capable of much higher speeds just by keeping the water in the lake. One day though, a cabin along the beach caught fire and a guy with a jet boat saw the burning house. He backed his boat in near the shore, trimmed the boat to make a very large rooster tail and shot water at the cabin which was way up on the bank. While using his steering and trim to direct the water at the flames, he proceeded to put the fire out. The boat did not accelerate forward according to your second rule, it just inched along; in fact, he was able to apply full throttle with minimal movement of the boat and he put the fire out in under three minutes. Albeit, he had to back up a couple of times. The reason that the boat didn't go shooting across the lake was not because the water wasn't being accelerated (it was); it was because there was only a small build up of pressure behind the water jet when pushing it through the air as opposed to a large build up of pressure when pushing the water into more water. The size of the rooster tail out the back really DOES matter!
Bro just talking out his ass😮💨 tryna make a dollar out of a 15 cent hair piece☠️
How do we mount the water jet?is the outlet nozzle fully above waterline?
@@eduardodaquiljr9637 normally, no. You want the water jet outlet above waterline when running at speed. But if the pump is completely out of the water, it can't prime. (Prime = suck in the first water to get started.). Typical install: mount the water jet with the shaftline of the jet at the same level as the waterline.
Fantastic explanation.. But to help further my understanding... I expected the Action/ reaction and thrust component to need to react on water to provide thrust... Obviously the toy hoverboard did not have that... What is the other reasoning behind needing a nozzle to be low on the stern? My previous thinking was that the water stream reacted with the water for thrust.. But against air seems counter intuitive..? Any further help here? Thanks again. Casey.. ( trying to put together a mini jet boat out of PWC components..)
Well it really doesn't need to react on anything, if you think about a gun recoil it's pretty much the same principle. You have on one side your handgun providing a force to the bullet (action) and on the other the bullet providing force on your gun and by extension your hand (reaction), you will feel the same reaction independently of wether the bullet did hit the target or not. Same applies with this hoverboard here. As for the nozzle needing to be low I'm afraid I do not know either...
Lets say you needed a waterjet thruster rather than a propeller, for safety reasons, on a slow moving vessel (5kn). Would it still be necessary to have a nozzle to accelerate the water? Could not the acceleration take place in an axial flow impeller. Could it be, in this case, that a nozzle would converts high volume low speed to a lower volume with high speed and a potential loss in efficency. Another question: Judging from the shapes of waterjet turbineblades (not airfoils), are they so called supercavitation blades? Thanks for a amazingly clear and entertaining video.
To answer your question, yes you can absolutely place an axial flow impeller without a nozzle inside a tube for slow speed. Whether we would still call that a waterjet? I would say no, but it really is a debate of semantics and not about practical engineering. Even without the nozzle, the axial flow impeller will still accelerate the water. But if you are talking about protecting a propeller on a vessel moving at 5 knots, the more practical option is to just build a duct and cage around a conventional propeller, rather than build a bad waterjet. The propeller loses some efficiency due to the drag of the duct and cage, but it still does better than a bad waterjet.
To your other question: No, waterjet impeller blades normally do not use supercavitation blades. We normally want to avoid cavitation within the waterjet. The blades look odd because they are designed to work with the spiral flow pattern of the water as it gets forced through the impeller while in a tube. But if you look at the cross section of the blades, they look like regular airfoil shapes.
@@DatawaveMarineSolutions Thanks for taking the time to answer the questions in the comments. It's really interesting!
Fantastic video!
do these principles apply for a submarine? Does a waterjet propeller need no rudders?
Broadly, yes. The submarine equivalent is called a pumpjet. It's a little different to a waterjet. Waterjets are designed around operating on the water surface, with the jet outlet being above water, and the inlet on the bottom of the hull. Pumpjets pull water in from the front, on all sides. They are designed to operate underwater. And for submarines, the pumpjet tends to be most focused on silent operation rather than pure efficiency. I did a comparison video on this, which you can find here:
ua-cam.com/video/Y8kJKL5M8ug/v-deo.htmlsi=l7sGMBXD4G_Va0VP
And does a waterjet need a rudder? Usually, no. The waterjet usually has a bucket, which redirects the outlet stream. By changing the angle a little to the left or right, we can turn the boat. But pumpjets normally don't have a bucket, because it makes too much noise underwater. So submarines with pumpjets still use rudders.
Thanks learned a lot!
Rooster tail doesn't matter in terms of thrust, true. However the angle of the rooster jet changes the trim angle of the boat which can increase planing efficiency (or make it worse!).
Good point. I'll remember that for future planing hull designs.
How well would this design work in air? Can it power an aircraft at supersonic speeds? Thank you!
Your modern jet engine works on the same basic principle as a waterjet. The intent is that water exist the waterjet faster than it entered. The same is true for a jet engine: air exits faster than it entered. But how you achieve that goal works completely different in air at supersonic speeds. If you take a waterjet design and apply it straight in air at supersonic speeds, it will deliver exceptionally poor performance.
@@DatawaveMarineSolutions Thanks! I'm actually interested in a supersonic electric jet. And since propellers doesnt work well at those speeds, I'm looking for alternatives. But I guess a jet engine that only compress the air without the combustion process is a bit silly.
Is there any way to make a supersonic electric jet at all? (assuming battery improvements obviously)
@@temporaryname8852 Excellent question. And, unfortunately, outside my field of expertise. I'm not sure how you would generate sufficient thrust. Fundamentally, the combustion process just imparts heat to the air, causing expansion. In theory, you could achieve the same effect with an electric arc across the air path. But it would take a LOT of a high voltage electricity.
@@temporaryname8852 I don't know if you're still interested, but an electric jet drive like you describe is fine in principle. The turbine in a jet engine isn't adding to the thrust. It consumes energy, so by removing the turbine, and driving the compressor mecanically, you get more thrust. A lot of supersonic planes already do this in a way. Even most fighter jets now have turbofan engines, where the core engine produces torque to drive the fan, which just shoves air through a nozzle without any fuel or heating to produce extra thrust. This is done for improved efficiency.
In principle, you can get rid of the turbine and use an electric motor to drive a fan with a nozzle behind and you could even go supersonic with enough power on your motor. In practical terms it's fairly hopeless, because the electricity needs to come from heavy, bulky batteries. Battery powered planes are marginal even for slow prop planes. They get some use as trainers, since those don't have to fly far, but if you want to go faster, you need more power, which means range gets even shorter, to the point it would be useless for anything but a stunt. Batteries also have a maximum power output, so to power a supersonic jet, no matter how briefly, you'll still need a huge weight of batteries, which will make it difficult to fly in the first place.
I think maybe an RC plane, or a very small manned one could maybe do it for a record setting run, but it just wouldn't be practical for any real uses.
hello. do you have any idea what company/brand that has good pump and nozzle?
My kyack with a human powered water jet needs the correct size nozzle
ForThe 2 bilge pumpS I think I can pump 20 gals on each pump for a little while
At 40 psi I think I need a 1/2 inch nozzle for each pump is that about rite.?
When I see that rooster tail and the acceleration, I worry about the suction power of waterjets. Do you have to install a grate to protect against fish getting sucked in...or people? But I know a conventional propeller also creates a lot of suction current and can be dangerous for people and fish too. Maybe you can make an addon video about what are the metrics of suction and how do you calculate how much is too much?
PS, waterjets are cool, but icebreakers are cooler (literally). I hope you get to icebreakers soon.
You can see the grate on the intake in the video. But yes, you need something there. Small jet boats are notorious for sucking lines into their impellors, and it's a PITA to extract the mangled remains of the line from the system. Bigger jets normally means a bigger boat and bigger lines... and are probably even harder to untangle. Fish I suspect are less of an issue because they're bulky and easier to filter out, plus they're softer so they will tend to just pass through the jet and come out as a cloudy pool of water...
most jets have some sort of filter for stuff that can harm the pump
When a water jet driven boat speeds over a dense growth of water weeds or water not deep enough over a mud flat the water inlet becomes clogged and the boat stops. In the case of the now antique River Patrol boats as used in Nam fifty years ago the diesel driving the thing explodes as a connecting rod tries to leave the engine. This can be very exciting.
Question, with water jets would an internal voith thruster work with more or less efficiency?
Probably less efficiency. The Voith thruster is designed for slower flow, so the blade designs would be all wrong.
Are there any specific rules for designing the size of the jets inlet with respect to the nozzle diameter? I know the inlet velocity plays a big part but I'm trying to design a pump and need a decent starting size. Any help with be appreciated :)
What would happen if enough micro electric waterjets (from RC boats) were installed on a regular boat? Would that be more efficient?
Probably not, for two reasons. First, the RC jets can't afford the engineering cost to optimize a jet to the same degree as a commercial jet. Second, consider the weight of the electronics and motors to distribute that power to all the jets you would need. That would also reduce the overall system efficiency.
Love your videos bro
I had an interesting discussion with my friend. I claimed through what I learnt here that it does not matter where the water is pushed. But how come the jet is always pushed down to the water? Is it only to make the water jet not touch something else?
The physics will always work. You can place the pump 5 m above water level, and the basic physics of a waterjet still work. But the location of the waterjet does have a strong influence on the efficiency. It takes energy to pull the water above the static waterline. Quite a lot of energy, because waterjets need to do that with a huge flow rate. So a waterjet 5 m above waterline is much less efficient than a waterjet only 0.5 m above waterline.
Sorry if the video mislead you. For brevity, I don't cover all the nuances of each subject. Otherwise, I need to recreate an entire college class.
@@DatawaveMarineSolutions thanks! No problem, real happy with your videos.
Thanks!
Nick - are you going to do something on the Evergiven?
Probably, yes. I don't normally do reaction videos or commentary on current events, because it can be too easy to jump to conclusions. But I am considering a video about the physics behind the grounding and the salvage operation.
@@DatawaveMarineSolutions Great: That's what I was thinking - there is a lot of questions around how ship dynamics precipitated that situation. Always enjoy your 'lessons'.
Does impeller generate pressure though, i think that impellers generates kinetic energy on the fluid which which increases the flow, by inducing kinetic energy its then transferred to more kinetic energy and less pressure in nozzle. Hope somone approves or agrees to my answer, because i know for sure that pressure in pump is a measure of the resistance not the impeller.
Another question will surface roughness affect the performance of impeller?
I made an RC boat with a waterjet, and above a certain throttle point, the jet would completely lose all thrust. I believed this to be since the boat started to ride out of the water and the inlet wasn't, getting enough water to suck in by the pump. Does anybody have any suggestions, I'm sure this applies to real life.
Maybe adjust the trim to put the inlet deeper in the water?
So when should one go for a waterjet rather than a propeller if basing the decision on efficiency?
Great question! I answer that in a separate video that specifically targets the questions of waterjet efficiency: ua-cam.com/video/fNNYUq5M-z4/v-deo.html
@@DatawaveMarineSolutions
Ummm ... okay, so I have this incredibly stupid question of no real importance ... if I'm interested in "efficiency" in the sense of fuel economy, why should I *EVER* consider using a water jet over a prop (at least in the absence of having committed to having a big honking fuel hungry gas turbine as the ship's engine)?
I mean, yes, F = m * a shows that you can get the same amount of force (thrust) from either accelerating a large mass a small amount OR accelerating a small mass a large amount ... *BUT* the kinetic energy of the accelerated mass is described by the equation KE = (1/2) * m * v * v and so small changes in v (which is the acceleration caused by said propulsive element be it a prop or an impeller) turns into very large changes in kinetic energy very quickly.
And since that energy has to be delivered by the engine, and that energy comes from converting the chemical energy of the fuel into mechanical energy delivered to the propulsive element, that means that for a given energy input, acceleration a small mass by a large amount is always less "efficient" in the fuel economy sense of the word than accelerating a large mass by a small amount.
So in the case of air instead of water, a quad copter with relatively small diameter props is almost a stupid idea compared to a helicopter with a single larger diameter prop, at least when it comes to "efficiency" as in getting the most lift for the amount of energy in your batteries or fuel.
So what am I missing here?
Why can't I beat the crap out out of any water jet in terms of fuel efficiency by just making the prop or props larger in diameter?
Is it that you can only go so large in increasing prop diameter in water before cavitation sets in?
And if cavitation is the culprit, then why isn't this justification for using a prop that doesn't move in a circle like a lifting vane configuration?
@@lewiscole5193 In your logic, one major factor to include is that the efficiency of a waterjet / prop is not uniform across all speeds. In general, you are correct that a large diameter propeller beats a smaller propeller in efficiency. And at lower speeds, a propeller beats a waterjet in efficiency. But at higher speeds, the efficiency of the propeller drops off and the waterjet efficiency improves. Eventually, the waterjet becomes more efficient than the propeller, at high speeds.
@@DatawaveMarineSolutions
Thank you for your response.
At the outset, let me say that I'm not a naval architect and I don't play one on TV.
What I am is someone who has been interested in aircraft forever and who once upon a time thought about designing and building one of my one.
So I have a basic familiarity with aerodynamics and aircraft history and what I'm curious about is why something that applies to aircraft doesn't seem to apply to ships rather than to start an argument.
So back to your response.
I think, we are talking at cross purposes here as I'm *NOT* talking about "efficiency" as it's usually defined, namely the ratio of power out (usually denoted by eta[o]) to power in (usually denoted by eta[i]).
Instead, I'm referring to "efficiency" in the sense of "fuel economy", and in this case, both Newton's Second Law and the definition of kinetic energy don't give a damn about "efficiency" at some particular speed or even over a range of speed.
Both equations together indicate that it is *ALWAYS* more "efficient" in terms of minimizing the amount of energy you have to deliver to the propulsor element to get a given thrust by accelerating a larger mass to a smaller speed than to accelerate a smaller mass to a higher speed.
In short, a larger prop *ALWAYS* wins out over a smaller prop (or jet impeller) for any acceleration (which is what "v" in the equation for kinetic energy really is) independent of propulsor efficiency at some particular speed or speed range.
In the case of aircraft, a prop powered aircraft always wins out over a jet powered aircraft so long as the jet's fan is of a smaller diameter absent some other consideration(s).
Even today, virtually all smaller air liners are always prop driven even though they used turboprop engines rather than Otto cycle engines.
And in the case of larger airliners, large "props" still win out as that's what the fan at the front of a high bypass turbofan engine really is (albeit a prop in a duct) compared to low bypass turbofans or pure turbojets.
Even larger "unducted fans" are better still where such props have a scimitar shaped blades to reduce losses from shockwaves on their surface.
It is not efficiency (or the lack there of) that has prevented these "unducted fans" from appearing in anything other than test aircraft, but rather noise.
So, getting back to the issue at hand.
Even if a jet of some diameter is more "efficient" at a given speed than an identical size prop, I should always be able to beat the jet simply by increasing the diameter of the prop OR increasing the number of props absent some other consideration(s).
And whatever the "efficiency" of a water jet might be at some "higher speed", it would seem to me that a larger prop should still be an option ... after all, as far as I know, all of the non-gas turbine powered hydroplanes are powered by props rather than water jets which I would assume would not be the case if a jet's efficiency advantage at higher speeds were overwhelming compelling.
That gets me back to lifting fans.
Once upon a time, Lockheed proposed their "sternwheeler" jet transport called the Omega which used lifting fans rather than either props or jets for propulsion.
Not having to move each of the lifting blades in a circle where one end was fixed at the axis presumably should have reduced/eliminated compressibility as an issue for said propulsor.
And if cavitation is what limits prop diameter on a ship (is it?), then a lifting fan should be able to move more water without cavitation getting in the way.
In the case of the Omega, presumably the expense of getting an airworthiness certificate got in the way of its lack of further development, but no such constraint presumably exists for a ship and so I'm left wondering why I haven't seen even a proposal for a lifting fan powered ship.
So can you please wave your arms at the discrepancy again as it does *NOT* seem that "efficiency" at higher speeds is a particularly good answer to my question(s)?
@Lewis
1. The way to maximize fuel efficiency in any engine is to switch it off.
2. If motorbike can get 80 mpg. Why would anyone drive a car, or lorry?
3. You say a bigger prop is better, but you seem to forget it's also bigger, ie heavier, and needs a heavier thing to hold it and a heavier thing to turn it. You can't strap an A300 Airbus engine to a little Cessna - it'd collapse.
Nick do you think it's even possible to fit water jets on the ss United States ?!
Probably not. The stern shape of the ss United States would make it very difficult to fit in a waterjet. Technically, it is possible. But it would probably be a waste of effort.
Yeah good point.
I have a stupid question. Lets say i was doing a restomod of a 1957 chris craft. I wanted to take the jet pump from a jet ski but have it ran by the 131 hp engine. would the jet even work given lower rpms of the larger motor?
Not a stupid question. Unfortunately, too complicated to answer without detailed knowledge of the jet, hull, and the motor. But you are correct to consider the problem of lower RPM from the motor.
The best way to test all of these theories is to make it out of pvc. If you can make something half as large out of pvc then you can figure out nozzle size and intake shape and so on
If someone were to put Jets in a 1961 Hatteras 41, is that crazy talk? Would 1 large jet be better than 2? How much HP/KW would be best?
You'd definitely need 2 jets. 1 jet would not maneuver very well at all.
Thanks you help rid of my insomnia!!!!
Is there any reason the intake section of the waterjet couldn't be longer? I have my reasons which I'm not quite ready to divulge.
If you would like a confidential discussion, you can contact me at sales@dmsonline.us. I can prepare an NDA to protect any confidential information you share.
has this resulted in some sort of product?
How does maneuvering in harbor effect harbour floor?
Depends on the bucket design .. and of course how deep the harbor/marina is. Some buckets direct the jet straight down in neutral, other direct it only slightly down but mainly to the sides .. the ones that shoot straight down could definitely disturb the floor or worse a reef ..
Can we install this in conventional Tug boat ?
Technically, yes. But there are other options that are more efficient for a tug. Options include conventional propeller, controllable pitch propeller, azipod, or Voith propeller.
To answer your questions. I'd employ you.
1 一级的叶轮 不可能有太高的出口压力，否则效率会下降。
2进口的压力，极限为真空，
3叶轮的直径与转速受到，气泡的极限限制
中国有生产，但是水平比较基础。我已经转到表面效应桨的研究。
Sadly, Google translate did not do this justice. Sorry, I do not speak Mandarin / Chinese characters. From Google translate, I understand the basics.
1. Impeller pressure relates to efficiency.
2. Inlet of impeller, minimum limit is vacuum pressure. Agreed.
3. Cavitation of impeller. Something about surface effects.
I wish I spoke the language.
@@DatawaveMarineSolutions "1. First impeller won't have too high of an exit pressure, or the efficiency goes down.
2. The limit of the pressure at the inlet is vacuum.
3. The diameter and RPM of the impeller is ultimately constrained by cavitation.
China has production, but the quality is basic. I have switched to the research of surface drives"
Might have made some mistakes, not specifically my field of study.
With potential for 90% efficiency I am thinking a matched design of electric motor and water jet (vs propeller) on a blue water sailing yacht, say a NEEL 45 or 47 trimaran, or similar catamaran (light weight, low drag) might make electric powered propulsion viable. Solar, wind, and water electric generators for ongoing recharge. Add an appropriately sized genset for backup.
You have to be careful. The PUMP is 90% efficient. The waterjet as a whole is around 40 - 60% efficient, depending on the model you select and how you use it. Remember that the pump only generates pressure. The rest of the waterjet still needs to convert that pressure into thrust, which involves some additional efficiency losses.
I think the ideal configuration would be a trimaran superyacht with 5 waterjets.
Can you link your hairstylist please.
Sorry. I do my own hair.
how much it costs
That blogpost on your website regarding software seems quite extensive, it has been bookmarked for when i am able to manifest my idea to reality.
Not a great shape for water jet impeller at around 7:00. Most important to add ... gap between impeller and the water jet wall or pipe is SUPER CRITICAL. The gap has to be really small. Stator is NOT optional.
Professor Snape is here...😂😂❤️
So a waterjet is actually more like a rocket, as in the propulsion comes from it shoving a load of mass out of the back, ergo it would work in space (if it had a water source)?
Exactly. The rocket is a great analogy.
It works like a jet, not a rocket. Rockets don't suck in air/water, that's why they work in space.
@@sepg5084 No because a jet in part gets it thrust by pushing against the existing atmosphere and causing an overpressure. Whereas a rocket relies solely on the expulsion of mass at high velocity.
Thanks for explaining but we still dont know how to build a waterjet without the formula's to calculate it😅
Dear friend make a video explain "SEA GOING AND RIVER VESSEL".... very few info online; just broker advices... i think very few people know, most of the little info online is from North Europe and former USSR countries. flat advices from design bureau of Germany, Sweden, Netherlands, ... nothing really clear and good explain.
Титры сделайте
Where ar de vídeos ande de 3D model? You talk to much!
Were is the math?
As a general rule, DMS doesn't include the mathematics in the presentations because several of the engineering concepts can be implemented incorrectly when taken take out of the larger context of a full education in ship design. If you are interested in the mathematics, the video description lists several references used to create the presentation. Reference [2] would be a good starting place.
Hi, I'd like to build a water jet that operates BELOW water. Like this one aerofoils.de/ You say that the efficiency drops off - can I simply enlarge the nozzle to reduce the hydraulic locking effect below water? Or just operate with no nozzle effect at all turning it into a ducted impeller?
Thank you very much, very helpful