Sine wave propulsion

[JonathanCole]

Living in Hawaii I do a lot of diving. Quite sometime ago I started swimming underwater in an undulating, sine wave motion and noticed a dramatic increase in the speed I could swim versus simply kicking my fin-shoed legs and flapping my hands.

So I started to think about one of the sea creatures that uses such a mode of propulsion - the manta ray - and realized that it was possible to create such an underwater motion by encasing springy skeletal pieces made from carbon fiber (like fishing rods) in an undulating, flexible propulsion mechanism cast from silicone. Has anyone heard of any work like this being done for marine propulsion? Being flexible it may be more durable as well, in addition to being less injurious to sea life and swimmers.

Here's a sketch of an underwater craft that might use such a propulsion system. However, if I am correct about my sense of the efficiency of this general means of applying thrust to water, it could be also advantageously used for regular boats and ships. Any ideas?

[Skippy]

I thought all fish swim that way. Except most fish's bodies form one cycle only (or less), and their motion is horizontal rather than vertical.

Here's one project: RoboTuna (http://web.mit.edu/towtank/www/Tuna/tuna.html)

[cyclops]

Most engineering schools have yearly contests in which the submarines are all propelled that way. VERY efficient mode. Mother Nature wins another one.

[JonathanCole]

I thought all fish swim that way. Except most fish's bodies form one cycle only (or less), and their motion is horizontal rather than vertical.

Here's one project: RoboTuna (http://web.mit.edu/towtank/www/Tuna/tuna.html)
Thanks Skippy. Check out these excerpts from the M.I.T. Robo Tuna that are at that link. (color highlights added by me)

"The experimental results of tests clearly demonstrate that RoboTuna duplicates Gray's paradox (i.e. the drag of the swimming fish RoboTuna apperars to be less than the drag on the straight RoboTuna), but does so with unarguably "known" mechanical muscles. These experimental results, at least for the parameters tested, support Gray's claim that differences in marine/terrestrial muscle power are not the answer, but do not go so far as to explain what the solution to the paradox is. However, it does lend strong credence to the possiblity that some form of unconventional, highly beneficial hydrodynamic mechanism exists, which reduces drag in fish-like propulsion.

Based on this background, consider the fundamental questions raised, by the biological data, and how the Tuna's experimental results address them:

1) Can the flow past an undulating body propelled by an oscillating foil be "tuned" such that the body's drag is reduced and its thrust is enhanced in a beneficial way?

Yes, clearly it can be, as both Gray's paradox suggests and the results of RoboTuna's experiments conclusively show, this flow can be altered by the correct body-wave/tail-foil motion to use the hydrodynamics in a benificial way.

2) What are the parameters which control this tuning?

In the case of the RoboTuna the parameters which control this tuning are the set of traveling body-wave/tail-foil control parameters given by: *the forward speed *the tail fin's maximum angle of attack *the wavelength of the travelling body wave *linear amplitude of the body wave *a set of fluid dynamics parameters. These may not be the only or the optimal set of such parameters. As with coordinate or modal systems, there is probably an infinite variety of ways to express the same charateristics, but this particular set is eplicitly tied to body dynamics, in such a way as to be easy to observe, to measure, and to comprehend.

3) What is the maximum benifit that can be achieved?

Gray's paradox implies that a seven-fold reduction in drag be acheived. The RoboTuna only experimentally reduced its drag by about half. Obviously Mother Nature is the better engineer. For the sake of argument, assuming the RoboTuna has a purely internal mechanical efficiency in the range of 90%, by extension, it can be claimed that its apparent reduction in drag is in fact probably in the range of 60%, but obviously, there may still be a way to go.

4) Can a man-made (non-biological) system successfully exploit this phenomenon?

Yes, as the RoboTuna clearly demonstrates, it can. But a more appropriate question based on the Tuna's results is now; What level of performance can be acheived by a man-made system, redesigned based on the information collected during this phase of the program? These results also raise a host of intriguing new questions such as; What happens at higher speed?, What is actually going on in the flow about and behind the body?, and Can this be replicated in a free swimming fish?" So if there is a potential 7 fold reduction of drag, how come nobody is working on it for the real world? The price of "unlimited petroleum? Or is the problem to complex?

How about a vessel with three hulls. The two outer hulls are standard catamaran hulls (but super fine, thin, deep) and the center "hull" is an undulating propulsion mechanism. Perhaps it is operated by motor(s) or perhaps by a wind power device. With super low drag, in a SWATH design the sine wave hull might leave other designs in the mist. Any thoughts?

[cyclops]

Lets not ask more of Nature than she wants to give. Maximum speed about 60 mph with tunas and Makos as large and eff.

[JonathanCole]

Lets not ask more of Nature than she wants to give. Maximum speed about 60 mph with tunas and Makos as large and eff. 60 MPH is not too shabby a goal.

Imagine a wind collector on a boat that would be a row of masts (shorter than the usual length). They would be set up to pivot on a ball socket that would only allow side to side motion. They would also be attached together by some elastic medium (Like a bungee cord) which could be adjustable in terms of the height above the pivot point. The masts would have a wind collecting surface of some desirable shape and square footage that would collect the wind and cause/allow the masts to wave side to side, constrained by the elastic interconnects. The masts would continue past their pivot points into a flexible hull (this hull might even be a 2 dimensional flat sheet) where the mast ends would be firmly attached. Being constrained by the elastic interconnects and ball joints, allowing movement only on the plane perpendicular to the axis of the hull, a sine wave motion would ensue in the collectors and thus in the flexible hull.

By moving the elastic interconnects higher or lower you change the wave amplitude which determines power. By changing mast spacings you change wavelengths. Longer wavelengths for higher speeds, shorter wavelengths for lower speeds.

If there is no wind, a simple crank (not me, I'm a complicated crank) interconnect from a motor, or even hand driven could set the craft in motion. I have seen art mobiles that create sine wave motions like this atop the entrance to the subway in Porter Square in Cambridge, Massachusetts. So it definititely can work.

[cyclops]

And I thought I am a design thinking "out in orbit somewhere" person. I am a child.

[VladZenin]

Sine wave propulsion...
...Here's a sketch of an underwater craft that might use such a propulsion system. However, if I am correct about my sense of the efficiency of this general means of applying thrust to water, it could be also advantageously used for regular boats and ships. Any ideas?
Jonathan,
I can suggest a simple propulsion device for Manta ray submarine. Do you know people that will be very interested in such a project?

[Leo Lazauskas]

And I thought I am a design thinking "out in orbit somewhere" person. I am a child.

But in the Kingdom of the Blind, you are King!

[masrapido]

Jonathan Cole,

If you read my posts, you'll see that I did not say it is impossible. I said that it is not practical idea. First you suggested that I want it strapped to my feet, what is exactly what VladZenin was suggesting, read his original post; and then you claim that I did not understand the thread. Well, imagineer, you better wake up and read better yourself. Because, as I said then, this idea IS unpractical. It has been tested in late 80', admittedly the movement of the "propeller" was horisontal (from left to the right and back).

But, as they (some team somewhere in US, at some university - come on, it was long time ago. Can't remember everything.) said then: the movement IS efficient. But unpractical because propulsion IS strapped to the rest of the vessel and, as basic law of conservation of mass says, if you push something with a force, something will push you with the same opposing force.

Which part of the law you do not understand?

Now, the future is probably in a screw type of a propeller because rotary movement can achieve speeds and reduce vibrations a lot better than just a vertical movement. Rotations tend to create less vibrations to start with and when a certain speed is achieved (y'know, resonance and frequency thing) vibrations disappear.

No amount of linear movement can beat rotational movement.So, for the comfort sake I will look for propulsion other than you discuss here because, while commendable, it is simply not practical for human transport.

But, you feel free to keep imagineering. Galilleo dreamed about parachute and helicopters long before they became functional.

[JonathanCole]

But, as they (some team somewhere in US, at some university - come on, it was long time ago. Can't remember everything.) said then: the movement IS efficient. But unpractical because propulsion IS strapped to the rest of the vessel and, as basic law of conservation of mass says, if you push something with a force, something will push you with the same opposing force.

Which part of the law you do not understand?....

But, you feel free to keep imagineering. Galilleo dreamed about parachute and helicopters long before they became functional.
I think you are leaving a lot of things out of your analysis, but I don't want to rehash all that has been said in these various speculative and imaginative conversations concerning unconventional propulsion. You have a right to your opinion, all though your attitude is not one that lends itself to constructive brainstorming. Maybe you should avoid these types of speculative threads. In any case, the guy in the picture below doesn't see it your way!

[VladZenin]

Jonathan Cole,
Now, the future is probably in a screw type of a propeller because rotary movement can achieve speeds and reduce vibrations a lot better than just a vertical movement...it is simply not practical for human transport...If you don’t like a vertical movement change it on horizontal. Black Tuna has length up to 3 m and swims with the highest speed about 80 km/h; Swordfish is up to 4.0 m length and swims under water with maximum speed about 96 km/h. Could you tell us please what kind of propeller do you need to push these fishes through the water with such high speeds? How much energy/fuel do you need for a circumnavigation with these propellers? Could you tell us please what will happen in marine environment if all creatures will have propellers? Why a human being does dominate over marine environment and does not reckon with marine creatures? In that way we do harm ourselves. We kill creatures and destroy marine environment. If a man made sine wave propulsion devices are still not practical for human transport, you can create the better one and I am sure you will be rewarded for this generously.

[masrapido]

JonathanCole.

What, just because I offeer a different view and one that clearly shoots your fantasy down I have an attitude? What cind of discussion is that?

You came up with an old idea that was proven in 1980' as doable but unusable and unpractical for application in human transport and I draw you attention to its' defficiency. If you are unable to discuss negative aspects of your idea like a reasonable person, maybe you have attitude problem and should not be participating in forums like this.

Be nice and ask an engineer about some basics in physics and then feel free to apologise. There's a reason why airplanes do not flap their wings; it's the same reason why boats will not "swim" like fish do.

Instead of availing to offensive remarks and inappropriate comments, try to learn how to accept limits of your knowledge and try to learn from others. That is what these forums are for, not for people like you to abuse other people just because your lack of knowledge means nothing to you.

Now, if you have something technical to discus, and counter my suggestion, offer a technical solution for problems or offer solutions that make this type of propulsion useable for human transport, I am more than willing to listen. But if you don't, at least please respect this forum and abide by the rules about the language you use towards others.

[masrapido]

JonathanCole.

What, just because I offeer a different view and one that clearly shoots your fantasy down I have an attitude? What cind of discussion is that?

You came up with an old idea that was proven in 1980' as doable but unusable and unpractical for application in human transport and I draw you attention to its' defficiency. If you are unable to discuss negative aspects of your idea like a reasonable person, maybe you have attitude problem and should not be participating in forums like this.

Be nice and ask an engineer about some basics in physics and then feel free to apologise. There's a reason why airplanes do not flap their wings; it's the same reason why boats will not "swim" like fish do.

Instead of availing to offensive remarks and inappropriate comments, try to learn how to accept limits of your knowledge and try to learn from others. That is what these forums are for, not for people like you to abuse other people just because your lack of knowledge means nothing to you.

Now, if you have something technical to discus, and counter my suggestion, offer a technical solution for problems or offer solutions that make this type of propulsion useable for human transport, I am more than willing to listen. But if you don't, at least please respect this forum and abide by the rules about the language you use towards others.

[icetreader]

Sculling is an ancient and well known, simple human powered method of propulsion that uses sine wave propulsion, usually at the stern.
The Chinese Yuloh, Japanese Ro, Venetian Gondola and other examples from around the world are highly efficient and enable a single person to propel and steer fairly large and heavily loaded boats across long distances.

Yoav

[VladZenin]

Sine wave propulsion is very differing from sculling. After sculling people used paddle wheels. Oars and paddle wheels use the same principle of operation. Screw propeller forced oars and paddle wheels out of a modern sea and river transport. I think the sine wave propulsion will be next because it is the most efficient propelling means (see my thread 8191 “Fishes and dolphins are powerful propellers”).

[icetreader]

Sine wave propulsion is very differing from sculling. Vlad,
I'm familiar with your work and have been following the thread you started (BTW, I rated it 5 stars...http://boatdesign.net/forums/images/smilies/smile.gif )
The subject is both interesting and promising.
Paddlewheels, rowing oars and paddles have in common the fact the blade enters the water, pushes it backwards, is lifted above the surface and then brought forward to re-enter the next time.
Yuloh sculling is different since the blade is never lifted above the surface: It stays under water all the time and is moved in a way that's similar to the movemnet of a fish tail (horizontal, left-right).
See here:
http://www.simplicityboats.com/ScullYulohaboat.htm
The fact people have been using this principle for millenia proves that it works and should be further developed to be used in faster and bigger watercrafts as well as in small, human powered boats.

It seems a horizontal, left to right movement may be easier to implement in surface crafts than an up and down movement.
Here are two small, human powered boats making use of a concept that's reminding of sculling:
http://ondulo.com/
and
http://tailboats.com/

Yoav

[JonathanCole]

Jonathan Cole,

No amount of linear movement can beat rotational movement.So, for the comfort sake I will look for propulsion other than you discuss here because, while commendable, it is simply not practical for human transport.

But, you feel free to keep imagineering. Galilleo dreamed about parachute and helicopters long before they became functional.
Leonardo Da Vinci was the imagineer who thought up those things.
http://www.lairweb.org.nz/leonardo/
He actually did describe many devices that would be realized after his time. He is one of the most remembered creative personalities in the history of the world. He is a role model for me for over 50 years.

It is true that he did not overcome all of the practical impediments to seeing his ideas realized, but that in no way diminishes the genius of his work. All new developments arise as a series of steps taken by many people over the course of centuries. Sikorsky, the developer of the moderrn helicopter is said to have been influenced to do so by the work of da Vinci centuries earlier.

Just because something is not practical at a given point in time does not mean that the discussion should end because of the certainty of critics and skeptics. Why, among many millions of inventors and creative persons is da Vinci so outstanding? It is partly because he had a series of older mentors, who from the time of his youth encouraged and supported his "imagineering". I have been to da Vinci's birthplace (Vinci, Italy) and the museum there dedicated to his life. Without encouragement from others he never could have produced such a dramatically creative body of work. That is why I believe that in a collaborative creative design process (like boatdesign.net) it is better to be encouraging than disparaging. And masrapido, I had no intention of doing that to you, so if I said something to make you feel that way, I apologise.

Aloha from Hawaii,

Jonathan

[masrapido]

Yes, of course it was Da Vinci. No idea why I wrote Gallileo.

[VladZenin]

Vlad,
See here:
http://www.simplicityboats.com/ScullYulohaboat.htm
The fact people have been using this principle for millenia proves that it works and should be further developed to be used in faster and bigger watercrafts as well as in small, human powered boats.
It seems a horizontal, left to right movement may be easier to implement in surface crafts than an up and down movement.
Here are two small, human powered boats making use of a concept that's reminding of sculling:
http://ondulo.com/
and
http://tailboats.com/
I knew about http://ondulo.com/ and http://tailboats.com/ before and used to scull myself as stated in http://www.simplicityboats.com/ScullYulohaboat.htm but never knew that was ‘sculling’. You can see the sculler propels his boat by simply reversing his stroke. In fact the sculling oar works as a screw propeller blade. As long as the sculler makes oscillatory (not rotary) motion, he must turn the oar blade on a certain angle in each stroke (swinging propeller). It is easy to see the screw propeller blades have optimum position to create a directional water jet. Sculling cannot be efficient because the oar blade push water more up and each side then back. As to tail boats I see in them an approximate attempt to imitate fish locomotion.
There is no difference in efficiency of a horizontal and left to right movement of the sine wave propulsion device. We can use it this way, that way and every way.

[Frosty]

Is a surface propellor a rotating sculling device?

[VladZenin]

Could you make clear your question please?

[waveless]

When I was 16 years old, I had one year re-education in a boatyard. What was my working? my working was to make the oar for the boat! this is the most technique job in the boatyard, there were only one old master can do this job. every day I use a axe to cut a big wood to oar, it is reary a hard work. the oar use high quality wood, the wood had put in the room for many years, if the oar is distorted or miss designed, then you will got trouble that will very difficult to scull. the oar is much big than in the picture, it takes 3 month make one oar.

I think I am the only one can make this kind oar in this world.

[asathor]

then any form of wave based propagation is likely to turn out to be the most efficient because it is likely to have a higher energy conversion rate.

Waveless; please get yourself an apprentice or better yet contact the Viking Ship Museeum in Rolkilde Denmark http://www.vikingeskibsmuseet.dk/ I know they would love to have you teach someone your tecnique they have several boatbuilders employed there who do everything the old way by ax. You would feel like you were 16 again among those guys.

Maybe some of you math wizards can calculate the right amount of flex for sculling oar?

I suspect that the efficience will go up when the harmonic of the oar matches the stroke, it does in all other low loss resonance circuits. This is undoubtedly why Waveless was tought to buil the oars in one piece with continuous grain.

The fast fish are probably not using their muscles continuously - rather they use bursts of power that is released in a "wave" by their body. It would be interesting if someone who knows fish anatomy can contribute - I surely have not seen a lot of large blodvessels in the ones I have eaten.

[icetreader]

then any form of wave based propagation is likely to turn out to be the most efficient because it is likely to have a higher energy conversion rate.
Maybe some of you math wizards can calculate the right amount of flex for sculling oar?
I suspect that the efficience will go up when the harmonic of the oar matches the stroke, it does in all other low loss resonance circuits. This is undoubtedly why Waveless was tought to buil the oars in one piece with continuous grain.
The fast fish are probably not using their muscles continuously - rather they use bursts of power that is released in a "wave" by their body. It would be interesting if someone who knows fish anatomy can contribute -
Asathor,

Here's an article on the biomechanics of swimming fish: http://www.ece.eps.hw.ac.uk/Research/oceans/projects/flaps/swim.htm

Indeed, "harmony" seems to have a lot to do with this type of propulsion.
In terms of naval design maybe we should get used to think of the hull and the "propeller" (tail, fin, wing, oar - whatever) as two parts of the same thing rather than two completely different things?

Yoav

[JonathanCole]

Clearly different approaches to propagate the wave have differing advantages with respect to speed and maneuverability.

From: http://www.ece.eps.hw.ac.uk/Research/oceans/projects/flaps/bcfmodes.htm
Anguilliform mode

http://www.ece.eps.hw.ac.uk/Research/oceans/projects/flaps/images/spinyeel.gifAnguilliform is a purely undulatory mode of swimming, in which most or all of the body participates. The side-to-side amplitude of the wave is relatively large along the whole body, and it increases toward the tail.The body is long and thin, while the caudal fin is typically small and rounded, often missing altogether. The inclusion of at least one wavelength of the propulsive wave along the body, means that lateral forces are adequately cancelled out, minimising any tendencies for the body to yaw. Typical examples of this common locomotion mode are the eel and the lamprey.

[This cancellation of lateral movement is what I was trying to explain in another thread initiated by Vlad]


Subcarangiform mode

http://www.ece.eps.hw.ac.uk/Research/oceans/projects/flaps/images/trout.gifBody movements in subcarangiform swimmers (e.g. trout) are vey similar to anguilliform mode, the main difference being that the side-to-side amplitude of the undulations is small anteriorly, and expands significantly only in the posterior half or one-third of the body.


Carangiform mode

For carangiform swimming the body undulations are further confined to the last third of the body length, and thrust is provided by a rather stiff caudal fin. Since less energy is lost in lateral water shedding and vortex formation, efficiency is improved and carangiform swimmers are faster than anguilliform or subcarangiform ones. However, their turning and accelerating abilities are compromised, http://www.ece.eps.hw.ac.uk/Research/oceans/projects/flaps/images/clupea.gifdue to the relative rigidity of their bodies. Furthermore, there is an increased tendency for the body to recoil, because the lateral forces are concentrated at the posterior. Lighthill identified two main morphological adaptations associated with the minimisation of the recoil forces: (i) a reduced depth of the fish body at the point where the caudal fin attaches to the trunk (the peduncle) and (ii) the concentration of the body depth and mass towards the anterior part of the fish.


Thunniform mode

Thunniform mode is by far the most efficient locomotion mode evolved in the aquatic environment, where thrust is generated with a lift-based method, allowing high cruising speeds to be maintained for long periods. http://www.ece.eps.hw.ac.uk/Research/oceans/projects/flaps/images/skipjack.gifSignificant lateral movements occur only at the caudal fin (producing more than 90% of the thrust) and at the area near the narrow peduncle. The body is very well streamlined, while the caudal fin is stiff and high, with a crescent-moon shape often referred to as lunate. Despite the power of the caudal thrusts, the body shape and mass distribution ensure that the recoil forces are effectively minimised and very little sideslipping is induced. Although the design of thunniform swimmers is optimised for high-speed swimming in calm waters, it is particularly inefficient for other actions such as slow swimming, turning manoeuvres and rapid acceleration from stationary, as well as for turbulent water.

http://www.ece.eps.hw.ac.uk/Research/oceans/projects/flaps/images/bcf.gif

The gradation of the undulatory BCF swimming from anguilliform to thunniform modes (Source: Lindsey 1978).

[masrapido]

The only person qualified to talk about these speculative propulsions is the one that actually tested one.

http://www.dahlberg-sa.com/kd/Tail.htm

The rest of the bunch is just sauerkraut philosophy. And I apologise to all who recognise themself as such.

I wander what would Kjell have to say on efficiency and speed achievable.

[masrapido]

On the above: note the absence of waves, remark why is that, and that Kjell is using horizontal movement.

Also, Kjell has substantially solved problem with vibrations caused by tail-propeller movements. He paired them up, and I bet they are moving sinchronously in opposite direction to each other. One to the left, the other to the right. To reduce those vibrations that would make passengers sick.

His work is showing that there might be a way to use the PRINCIPLE ( of fish movement) to propell the boat/ship. Such propulsion may be adequate for work boats where advantages would be significant. As for the fast boats, I'd still stick with a rotary propeller. It turns full 360 degrees.

But I personally prefer sails for my boat. :cool:

[icetreader]

The only person qualified to talk about these speculative propulsions is the one that actually tested one. http://www.dahlberg-sa.com/kd/Tail.htm The rest of the bunch is just sauerkraut philosophy. And I apologise to all who recognise themself as such.
I wander what would Kjell have to say on efficiency and speed achievable. Masrapido,

1. Sine wave propulsion is not speculative since is has been successfully used in human powered boats for millenia (E.G. Chinese yoluh-sculling).
2. Kjell's research and findings are remarkable and they clearly suggest that this field is worth further investigation. Being a methodical researcher Kjell is likely to be the first to point to the multitude of related subjects that his research could not encompass, probably due to lack of funding. I'm sure we can all agree that it is regrettable, and he should have continued investigating. Even the limited set of variables he was able to check clearly merits a much broader investigation.
3. Other research done in this field adds to our understanding of the way sine wave propulsion works and clearly points to its potential.
4. There is no reason for us to assume that sine wave propulsion, when properly applied could not be used for fast boats, big ships etc. After all, in the natural world it is used by creatures ranging from microscopic size to 200 ton whales, and often in speeds that surpass our understanding.
5. As a boat designer and manufacturer I am grateful to people like Vlad and Jon who start such high-level discussions and "speculate" on technological subjects whose state of the art has not yet attained a commercial level. I find free-flowing discussions such as this to be both informative and intellectually stimulating, and therefore very useful.
However I can also understand why a consumer looking for a propeller for his boat may think of it as far fetched.

Yoav

[masrapido]

Hi Yoav,

Very interesting comments. I would like to point out to you that Vladzenin himself said that sculling is very different to sine wave. Also, it seems to be escaping to many that Vladzenin started his sine vawe debate by applying it to swimming. Debate took off, on a (tangential) vawe of enthusiasm, and turned into boat/ship debate. I would also like to point out to you that Jon believes this to be, dare I say, highly speculative subject/forum.

So, as we can see there's a multitude of opinions and even when some people agree on something, it may be for a whole set of different reasons.

In the meantime, I see nothing but theory in these, speculative or not, discussions. And on their face value, I cannot agree with what peole are saying. It is to far-fetched for a humble boat design forum. It does not contain any useful verifiable information, like tests, experiments, mathematical equations from which claims of efficiency were derived etc.

Many are obviously not familiar with ancient sculling, or they are missing the point here. Sculling is used on rivers for travelling DOWN the current. it is basically used for MAINTAINING the direction, not for propulsion. Venetian gondoliers actually use plain battons to push the boats because the channels are shallow. Yes there were some, with oars at the back, so what does that prove? They were used on boats for couples. Romantic, slow rides. Not dangerous US-style police chases around the channels of Venezia.

Try to scull up the stream and you will see that "classical" rowing is more efficient. As for the boats, where is the claim of being more efficient coming from? What tests, experiments trials? Against what comparable other propulsion? Oars? Show me the data, not some enthusiastic "This is revolutionary" sales pitch. Fish movement is complex, like bird's flying movement. And, as I said before, airplanes aren't flapping around the airports. Will be for a reason, wouldn't you agree?

Now, I like the work Kjell has done and there I see results that suggest possible use. He has tried it and is not making any bombastic claims. That will be for a reason too, wouldn't we all agree?

Why I say I'd stick with a propeller? Because propeller turns 360 degrees and is in uninterrupted movement, constantly providing the power. Kjell's experiments CLEARLY show that every flap has two zero moment positions where there's no work done. In a system of two flaps, there are four moments like that. Waste of time and energy because to move a flap into the opposite direction you must push it from zero. That requires a lot of energy. Not to mention braking energy loss from reaching the top of sinusoidal curve, if you know what I mean. Vlad, Jon?

As an engineer you should agree with these axioms. Hence, sine wave flapping is NOT as efficient as a propeller. By the nature of it's movement. One should be blind not to see it.

THAT is what I am saying. Of course it may help propell a boat reasonably fast, but at what cost? Instead of crying foul, sofa engineers and inventors should have a look at this and propose solution, if there's one (don't think so). Not clog the forum with links to experiments that have clearly failed to yield results, or debating fish in support of their unsupportable claims.

My remarks were not derogatory about the idea. My remarks, paradoxally, were constructive. Pointing at already identified shortfalls that budding inventors should have been informed about before going public with rather old ideas. I actually wanted to help.

But my remarks were not proven wrond. Simply refused with lots of noise. Noise instead of argument, we know what does that mean.

Since you are boat designer, would you share your technical expertise in analysing the merits AND shortfalls of this idea with us? That way we would have something technical, more scientific, to discuss.

Regards from ras rapido (faster in espanol)

And metrics please...Whole world is using metrics, those few imperialist left around, we'll get you...

[VladZenin]

masparido,
Here is a swimming Manta Ray RC robot from Japan. It flies underwater.
Japanese web site: http://www.imasy.or.jp/~imae/kagaku/
Watch some videos:
(http://www.imasy.or.jp/~imae/kagaku/manta1.mpg)
(http://www.imasy.or.jp/~imae/kagaku/manta2.mpg)
(http://www.imasy.or.jp/~imae/kagaku/manta_2.mpg)
You will love it.

[JonathanCole]

Also, it seems to be escaping to many that Vladzenin started his sine vawe debate by applying it to swimming.

That was me that started off this thread about swimming.

Debate took off, on a (tangential) vawe of enthusiasm, and turned into boat/ship debate. I would also like to point out to you that Jon believes this to be, dare I say, highly speculative subject/forum.

There are several other threads on similar subjects and I think you are confusing them.

So, as we can see there's a multitude of opinions and even when some people agree on something, it may be for a whole set of different reasons.

Then why do you seem so hostile, to people having a civilized conversation about technology related to boat design which some of the worlds highest institutions (M.I.T.) of learning seem to find merit in working on.

In the meantime, I see nothing but theory in these, speculative or not, discussions. And on their face value, I cannot agree with what peole are saying. It is to far-fetched for a humble boat design forum. It does not contain any useful verifiable information, like tests, experiments, mathematical equations from which claims of efficiency were derived etc.

Then it would make sense for you to not participate in a conversation that you find no value in.

Fish movement is complex, like bird's flying movement. And, as I said before, airplanes aren't flapping around the airports. Will be for a reason, wouldn't you agree?

That statement is so completely irrelevant to this conversation that it can only be meant to belittle the people who are taking part.

Now, I like the work Kjell has done and there I see results that suggest possible use. He has tried it and is not making any bombastic claims. That will be for a reason too, wouldn't we all agree?

No one is making any bombastic claims here except you.

As an engineer you should agree with these axioms. Hence, sine wave flapping is NOT as efficient as a propeller. By the nature of it's movement. One should be blind not to see it.

Unfortunately, the data does not support you. But you seem to be willing to say any unsubstatiated statement. Data presented on these various threads related to this topic and coming from top engineering sources have already refuted your position.

My remarks were not derogatory about the idea. My remarks, paradoxally, were constructive. Pointing at already identified shortfalls that budding inventors should have been informed about before going public with rather old ideas. I actually wanted to help.

Your remarks have been very derogatory to the participants in this thread, however. Not very helpful, friendly, constructive or polite.

But my remarks were not proven wrond... Noise instead of argument, we know what does that mean.

YES WE DO!!:rolleyes:

And metrics please...Whole world is using metrics, those few imperialist left around, we'll get you...

I think you have more hostility than is appropriate for this forum.


Aloha and peace to you,

Jon

[JonathanCole]

Here is a swimming RC robot Manta Ray from Japan. It flies underwater.
That is a very compelling presentation for anyone who doubts the utility of this line of inquiry! Thanks Vlad.

For anyone who does not understand Japanese, the videos are at the very bottom of the page that Vlad found. Just look for the words "4 MB MPEG" and such and then click on the underlined Japanese script right next to it.


(http://www.imasy.or.jp/%7Eimae/kagaku/)

[VladZenin]

Thanks Jonathan.

[icetreader]

Many are obviously not familiar with ancient sculling, or they are missing the point here. Sculling is used on rivers for travelling DOWN the current. it is basically used for MAINTAINING the direction, not for propulsion. Venetian gondoliers actually use plain battons to push the boats because the channels are shallow. Try to scull up the stream and you will see that "classical" rowing is more efficient.
Why I say I'd stick with a propeller? Because propeller turns 360 degrees and is in uninterrupted movement, constantly providing the power. Kjell's experiments CLEARLY show that every flap has two zero moment positions where there's no work done. In a system of two flaps, there are four moments like that. Waste of time and energy because to move a flap into the opposite direction you must push it from zero. That requires a lot of energy. Not to mention braking energy loss from reaching the top of sinusoidal curve, if you know what I mean. Vlad, Jon?

As an engineer you should agree with these axioms. Hence, sine wave flapping is NOT as efficient as a propeller. By the nature of it's movement. One should be blind not to see it.

Masrapido,

1. This is how the world understands what sculling is:
scull (skhttp://us.i1.yimg.com/us.yimg.com/i/edu/ref/ahd/s/ubreve.gifl)
NOUN: <>A long oar used at the stern of a boat and moved from side to side to propel the boat forward....
VERB:
tr. To propel (a boat) with a scull or a pair of sculls.
VERB:
intr.To use a scull or a pair of sculls to propel a boat.

Your interpretation about sculling being a method of steering downstream is factually wrong.

2. Since traditional sculling has been used mainly to propel relatively large-size and heavy boats (in human-powered terms) at low speeds (you can't have it all, unfortunately...) on flat or slow moving water it turned out to be a highly efficient method under such conditions: "...Indeed, at low speeds (approximately 1 m.s-1), the absolute amount of energy for propelling a gondola is the same as that for wa[l]king on the level at the same speed for a subject of 70 kg body mass."
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2347317&dopt=Abstract

3. No solution is perfect for everything, and rotational propellers, oars, paddles etc. have their weak points as well, as I assume you know.

4. Engineering formulas and "technical" data can be useful in various stages of developing a concept, from its hazy beginning to a final commercial product. However, they are definitely not the only means of thinking, creating or communicating. There is always a higher level of intellectual research and converstaion at every stage. "Gut feeling", imagination (visual and verbal) and unspecified inspiration play a crucial role in all creative processes, and dismissing them in favor of a "technical, engineering approach" is uninformed and simply unrealistic: You work with what you have from conceptualization to realization, and whatever contributes to your understanding and progress is good.
Ancient boat designers and builders didn't necessarily rely on mathematical formulas and even today some well known small boat designers still depend mainly on their "gut feeling" (at least that's what they say...). In some cases you'll find some of their designs have become classic ones in their field.
It's OK for you not to understand, like or accept this - nobody has any problem with that, but if you want to communicate with others in a respectable and more productive manner you will find that using a more moderate, relaxed and civil style can be quite helpful...

Yoav

[masrapido]

Joav and Jonathan,

Inability to understand is cultural and genetic. Your comments directed to a person speak all I should know about tring to discuss your speculations with you.

Sculling was born on rivers Yoav the boatbuilder. Not on the sea. We all know you live in a strange world up there. Fine.

Vlad, I did like it. I suggest we discuss these directly. Without the background noise of misunderstanding and hurt egoes.

Jonathan and Yoav, over to you for further expert display of personalised vitriolic comments. i realise you are to good for me to dare offer differing opinion. I apologise sincerely for thinking this to be possible. I deserve all your lectures and free display of absolute superiority. I will get now in line and will never dare to contradict you again. Promise.

[kjell]

When I was experimenting with flipping Tail Propulsion for boats. My model boats with different tails and tail movement’s was tested in a pool and recorded on video.
When looking to the videos, an interesting thing was possible to see. The boats normally make waves, but at one test the wave disappears. It seams that friction that produce the waver was reduced by the way the tail was moving.
http://www.dahlberg-sa.com/kd/index.html Tail Propulsion

[icetreader]

It seems I've been too careful stating that sculling is done in flat water.
This comprehensive article on the subject quotes some interesting examples of coastal sculling as well as more info on the efficiency of sculling as a method of propulsion:
http://councill.home.mindspring.com/sbjournal/sculling/scull3.html

From this article:

"...In the Bahamas, where fishing techniques and the narrow coral reef channels make it important to see where you're going, everybody sculls. They've even created a special stroke and oar for the job. In the Orient, the Chinese yuloh or sculling oar is the classic way of manually moving boats-- up to sampans of 60 feet and more!..."

"...And anyone who's traveled the New England coast has seen fishermen sculling dories or skiffs out to their boats."

"...As far as a yuloh's performance is concerned, an 18-foot Shanghai harbor sampan using a 13-foot yuloh could run at about 3 mph when propelled by one man. Roger Taylor, president of International Marine Publishing Co., has used a 10-foot yuloh on his 32-foot sloop Aria. He claims 2 knots in a calm, not bad for a 5-ton boat."

Enjoy http://boatdesign.net/forums/images/smilies/smile.gif

Yoav

[VladZenin]

When I was experimenting with flipping Tail Propulsion for boats. My model boats with different tails and tail movement’s was tested in a pool and recorded on video.
When looking to the videos, an interesting thing was possible to see. The boats normally make waves, but at one test the wave disappears. It seams that friction that produce the waver was reduced by the way the tail was moving.
http://www.dahlberg-sa.com/kd/index.html Tail PropulsionI think you have to continue this experiment to give yourself and us the right answer.

I want to discuss tail propulsion. Tail and fish/dolphin propulsion are very different. In fact fishes and dolphins are the travelling wave generators. A fish swims by moving its head from side to side, which sends wave down its body. This wave increases in intensity with the help of body muscles and finally reaches the tail, which then swings from side to side and propels the fish through the water. A dolphin moves head up and down and sends waves down its body in a vertical plane. Fish and dolphin tails at the time of their swimming push creatures all the time (see Force and Reactions Diagram in my reply for you in the thread "How fast..."). Tail itself (without flexible body) can’t do it. Flapping tail pushes water just at the time of it movement to the middle position. After crossing the middle tail push water left/right side and back. In other words after crossing the middle position it applies the brake to boat and causes turbulence.

[kjell]

After all my tail propulsion tests I come to the conclusion that to have a flipping tail or a foil outside a boat or a submerged hull is not a very practical solution. The experiment with the Tail-Jet is showing the possibility to take advance of the tail efficiency without the problem with exterior flipping appendices.

http://www.dahlberg-sa.com/kd/WJet.htm

[JonathanCole]

After all my tail propulsion tests I come to the conclusion that to have a flipping tail or a foil outside a boat or a submerged hull is not a very practical solution. The experiment with the Tail-Jet is showing the possibility to take advance of the tail efficiency without the problem with exterior flipping appendices.

http://www.dahlberg-sa.com/kd/WJet.htm
Kjell,

That video certainly proves the viability of your concept. Have you considered making a longer and more flexible tail (like a long diver's fin) that forms a sinusoidal shape as it is flexed. A point that Vlad has been making is that a fishes tail by itself does not account for the efficiency and speed of a fish/dolphin swimming capacity. If you replicate a full traveling wave in your device it should couple more powerfully with the water. You might have to have it in a tube with a square cross-section and perhaps flared at the outlet. I find this a very worthwhile line of research. As Vlad pointed out, such propellors are much less dangerous to sea life as well as being less likely to become fouled with debris.

[kjell]

(The long diver's fin) I only good for slow speed swim, the swimmer cant move his legs fast enough to get the benefit from a Dolphin tail. The shape of the undulation is very important to get the best propulsion effect.
http://www.dahlberg-sa.com/kd/Tail.htm

My tests in the Tail-Jet project include many variants, including different shape of tails and shape of the tube. If somebody like to work together with me in this project you are welcome.

[VladZenin]

After all my tail propulsion tests I come to the conclusion that to have a flipping tail or a foil outside a boat or a submerged hull is not a very practical solution. The experiment with the Tail-Jet is showing the possibility to take advance of the tail efficiency without the problem with exterior flipping appendices. You can see the screw propellers are exterior appendixes too but nobody makes Jet Systems with them. It will complicate a system and make it dangerous. Your pipeline can suck any objects in and propulsion system will be shattered. Excuse me, but this is not a very practical solution too.

[JonathanCole]

You can see the screw propellers are exterior appendixes too but nobody makes Jet Systems with them. It will complicate a system and make it dangerous. Your pipeline can suck any objects in and propulsion system will be shattered. Excuse me, but this is not a very practical solution too.
Actually people do enclose propellors for added efficiency and protecting the environment. There are many possible approaches to deflecting debris from the duct.

From: http://www.qis.net/~jmgraham/resrun.htm

"Reservoir Runners incorporate a ducted propeller system or Kort Nozzle. A Kort Nozzle features a hydrodynamically shaped duct, enclosing a high thrust propeller, to minimize turbulence losses and produce exceptional thrust and efficiency. The efficiency of a Kort Nozzle can be 50% to 70% higher than an open propeller on an electric boat, producing boat speeds 15% to 20% greater without using additional power from the batteries! At a given boat speed, run times are extended 50% to 70%. The propeller is also protected against hitting stumps and rocks, is safe around swimmers and won't tangle fishing lines. "

"Kort Nozzles A specialised ducted propellor system. The duct helps to derive more thrust then a open propellor in two ways. First, the duct inside diameter at the contriction is very close the propellor tips. This cuts down on energy loss from turbulant vortexes coming off the tips of the propellor. Second the duct cross section is shaped like an air foil. The water flow from the propellor moving through the duct generates thrust due to the shape of the duct. Water is forced through the contriction at high pressure which creates thrust as it flows to the less contricted exhaust opening. "

[VladZenin]

Thank you Jonathan. I see, for example HamiltonJet (www.hamiltonjet.co.nz) put up for sale 9 waterjet propulsion systems (http://www.nauticexpo.com/). I did not know about it. I ask for mercy for my ignorance. I am ashamed for that. It is impossible to stop a technological progress and a struggle for the market. It is known the mobile phones are dangerous for human health but they give us a lot of useful and necessary possibilities and we will use them.

[chenjh]

Oriental Scull was studied by 4 Japanese in a paper "Hydrodynamic Analysis of the Sweeping of a RO-an Oriental Scull" published in the Journal of Ship Research, Vol.33, No.1, pp.47-62, 1989. The authors are Azuma, Furuta, Iuchi and Watanabe.
They even measured a real boat's Ro. Its max efficiency is 0.43. The thrust is not continuous. During the reverse action of a blade (a short time period), the thrust is even negative because the blade's angle of attack is negative.

Beside, a Voith-SchneiderPropeller (VSP, vertical propeller) operating at high speed also make its blade traveling on a sine wave trajectory with varying attack angle. So, in a way of viewing, VSP is like a set of sculls operating together to provide continuous thrusst plus good maneuvering capability.

[kjell]

[QUOTE Why I say I'd stick with a propeller? Because propeller turns 360 degrees and is in uninterrupted movement, constantly providing the power. Kjell's experiments CLEARLY show that every flap has two zero moment positions where there's no work done. In a system of two flaps, there are four moments like that. Waste of time and energy because to move a flap into the opposite direction you must push it from zero. That requires a lot of energy. Not to mention braking energy loss from reaching the top of sinusoidal curve..[/QUOTE]

The limit of propeller efficiency is when the cavitations start.

The tail propulsion don’t have problem with cavitations. In the moment cavitations start on the suction side of the tail, do to the oscillating, this side is converted to pressure side and the cavitations stops. This gives the tail the opportunity to work with more efficiency than a propeller

[masrapido]

I agree with Kjell that cavitation should not trouble flaps, particularly not in a jet-type configuration. However I was refering to the power loss resulting from the movement, not from cavitation.

As I said, see quote, flaps have two dead/zero points where they come to a total halt and continue moving in opposite direction. Flaps draw water behind. To sustain the force of the water that keeps pushing them forward when they reach such a zero point and fight their way through that mass in opposite direction requires a lot of power. Twice as much. And then they face the same problem in the second zero point on the other side.

That is what I was talking about. And loss of power is the true measure of efficiency. Propeller is a lot more efficient because it does not have zero points. It only starts losing efficiency when cavitation sets in and separates it from the water. And we know that that happens at high speeds only. So for all practical purposes, on speeds below cavitation speeds, propeller works at its' optimum (almost, but that is negligible in comparison with zero points of the flaps).

[masrapido]

Just to add to the above: because of that loss of energy in zero points, fish bend their bodies and tails to minimise the impact of water trailing behind their tails. That is fine for fish, but applying the same solution to flap propeller would result in a very high level of movement in a vessel. Movements result in sea/air/car sickness as is, and being in a boat that bends left and right fast and with lots of force...I am not stopping you, but you might not have many passengers on your ferry.

[kjell]

Propeller propulsion efficiency has reached its limit and the efficiency of tail propulsion is still to discover: I am agreeing that an outside flap propeller is not the solution. That is the reason why I have started to make tests with what I call Tail-Jet Propulsion. It is some thing new and surprising.
http://www.dahlberg-sa.com/kd/WJet.htm

[JonathanCole]

Just to add to the above: because of that loss of energy in zero points, fish bend their bodies and tails to minimise the impact of water trailing behind their tails. That is fine for fish, but applying the same solution to flap propeller would result in a very high level of movement in a vessel. Movements result in sea/air/car sickness as is, and being in a boat that bends left and right fast and with lots of force...I am not stopping you, but you might not have many passengers on your ferry.
Any movement type creates an equal and opposite reaction. Even a propellor has rotary forces with the opposite reaction. In a sine wave propellor, any reactive motion can be cancelled by means of two devices operating in opposite phase, just as two props in opposite rotation would effectively cancel their induced reactive motions. This general principal is best demonstrated in a helicopter with counter rotating blades which allows for the elimination of a tail prop.

[masrapido]

chenjh, sharp observation. Do you have the document handy to share with us (a link to a page, or a copy of it somewhere? JC will enjoy me asking for a link...)

Kjell, I do agree with you. In fact that is the whole point that some are missing. Reading my earlier posts, I see how I may have been seen as aggressive against it, but I did try to explain that i was not against flaps per se. I tried to point out difficulties earlier serious researchers identified, and point out these to those who enthusiastically jumped on a bandwagon without giving it some analytical thought beforehand. Voight propeller is in some respects better than standard propeller but is not replacing it anyway. Will be for a reason.

And it does work along the flap-propulsion idea lines as chenjh rightly points out.

[tspeer]

Propeller propulsion efficiency has reached its limit and the efficiency of tail propulsion is still to discover: I am agreeing that an outside flap propeller is not the solution. That is the reason why I have started to make tests with what I call Tail-Jet Propulsion. It is some thing new and surprising.

I disagree. One can tell pretty well what the propulsive efficiency of a tail-jet is just from the geometry. I suggest you look at simple momentum theory. Here are some good sites:
http://www.grc.nasa.gov/WWW/K-12/airplane/propanl.html
http://www.mh-aerotools.de/airfoils/propuls4.htm

Although the web sites are written from the standpoint of propellers, momentum theory makes no assumptions as to what it is that is accelerating the flow. It could be a prop. It could be a flipper. It doesn't matter.

For the case of your tail jet, it's enough to know you have a tube with water coming in the front and going out the back. The simple fact is that thrust is equal to the change in momentum of the flow, which is the difference between mass times velocity in and mass times velocity out. Since the mass flow in has the be the same as the mass flow out, the thrust is also equal to the mass flow times the change in velocity.

For the same thrust, you can impart a large change in velocity to a small volume of water - the narrow diameter jet. Or you can impart a small change in velocity to a large volume of water, which is what a large span flipper does.

But energy is half the mass flow times velocity squared. The energy you have to expend is the difference between the energy of the flow coming in and the energy of the flow going out. For the case of the narrow diameter jet, the difference in velocity squared is high. For the same change in momentum - thrust - the flow leaves with a higher energy due to its higher speed. That energy has to come from the propulsion system, and so losses are high with a small diameter jet.

The most effiicient propulsive device will be one in which the change in velocity imparted to the fluid is small, so the fluid leaving the device is only going a little faster than it was when it came in. The trouble is, if you go a little faster, then the diameter is oversized and you incur drag. And even with a near-ideal sizing of the propulsor there are other losses. But momentum theory sets fundamental limits on the possible efficiency of any propulsive device even if what's moving the water has zero losses in its own right.

So a jet drive will always, always, always always have poor propulsive efficiency no matter what is inside driving the water. It doesn't matter whether it's a prop, or a flipper, or steam, or an undulating sine wave, or antigravity repulsion. There's nothing new to discover here. No surprises waiting to happen. It's a matter of conservation of mass, conservation of momentum, and conservation of energy.

It's not even true that propellers have reached the limit of their efficiency. Propellers are the size they are because if they are made bigger, the tips move faster and encounter problems like cavitation. But our growing ability to predict these effects means we can create designs that avoid them. That allows one to increase the diameter and improve propulsive efficiency.

The only way flipper propulsion is going to improve on the effiency of a propeller is by moving a larger volume of water at a lower speed. The external flipper can do this if the whole flipper moves, instead of being pivoted at the center. A propeller moves at low velocity at the center and high velocity at the tip. It's the high velocity at the tip that's the limiting factor.

So if the whole flipper translates, it's as though it had the average velocity of the prop, but not the same maximum velocity. So the flipper can be made larger without exceeding the speed limit set by cavitation. And larger is more efficient. Provided that the extra wetted area and weight/complexity of the mechanism doesn't get you first.

[jam007]

Tom Speer. Your mesage is (as always) an enjoyment to read. Clear well thought physics.
Both convincingly simple and eyeopening at the same time. Thanks

Anders

[kjell]

Hi Tom,
The theory is very good but what happen to the propeller efficiency when it receive turbulent water? Than the theory is gone. Flippers don’t have that problem. The pitch on a propeller is calculated on the incoming water speed and if the propeller is receiving a different water speed the propeller can’t give the output it was calculate for. I have over 15 years of experience with propeller calculation and resolving propulsion problems.

[jam007]

To Kjell:
Why isn´t flippers suseptible of turbulence?
How do the fippers generate their driving force?

I´m just an interrested bystander that want to learn more about physics and hydrodynamics

[masrapido]

yeah...tspeer, tread carefully. You are killing the speculative spirit of the forum. If you upset me mate JC, you'll be sculling south of the border on your own log. Mine is to small.

[kjell]

To jam007
I am glad that you ask this question. There are very little information how Flipper or Tails generates their driving force. The Tail is a fluid accelerator and works in a different way than foils. They are not working with the lift/ drag principle. The tail produces a fast pressure drop on its lee side and the surrounding water try to fill this vacuum producing acceleration. The mass of water has free way to escape without any obstruction producing a jet effect leaving vortices behind the tail. The drive force depends on the mass of water and its velocity.

[kjell]

Sorry this was the picture of the tail accelerator

[jam007]

Thanks. Kjell

Maybe I missunderstands but would not the fin create a high pressure on the opposite side as the low of equal strength?

[jam007]

Hm...
How fast can the fin travel from side to side? If it travels to fast you must get cavitation on the low presure side and that means that the mass in the low pressure jet must become almost zero and therefore the impuls drop dramatically.

Why are fish fins foilshaped?

There is something fishy here ;)

[kjell]

I have been testing with up to 50 Hz without any cavitation. As the low pressure side change to pressure side every cycle the cavitation has no time to build up.

[kjell]

I invite you to make a very simple experiment. Take a hand Fan and move it in front of your face, only 5 degrees on each side. The air you feel is the jet stream the tail is producing.

[JonathanCole]

I think it is worth pointing out that Tom Speer's critique is related to the ducted jet aspect of Kjell's device.

Another question is about the parasitic losses of the the water flowing through the duct. When a flipper moves in a duct it does not simply push the water straight back but sideways, as well. This may increase the friction/parasitic losses within the duct itself.

Another interesting question is since water is basically not compressible except perhaps for the gases within it, can you even talk in terms of a low pressure and hi pressure side? Wouldn't you have to describe the forces in terms of force vectors with varying or opposing directions?

Another point worth making is that Kjells device is not really the kind of sine wave propulsion device that originally inspired this thread, because the blade/fin is stiff. Although any point on a non-flexing fin will describe a sine wave once it is in motion, it does not reflect the way creatures generate travelling waves. The propulsor body part in a marine animals flexes in the sine wave shape. Whether tail&fin, body&fin or wings, the flex factor is always there. This is what Vlad was trying to explain in other threads related to this topic. I suspect (as Vlad does) that this travelling wave generator that marine creatures utilize has an especially advantageous affinity for the water medium. I think that it has to do with the way laminar flow works and in water there are issues of surface electronics/chemistry at the interface of the propulsor and the liquid.
See:
http://en.wikipedia.org/wiki/Electrical_double_layer
http://en.wikipedia.org/wiki/Laminar_flow
http://en.wikipedia.org/wiki/Turbulence
However to my knowledge, and in relation to interfacial electrostatic forces, no work has been done to quantify what happens to the interfacial electronic forces if the solid is moving through the solution.

[kjell]

The tail in my Jet device is flexible. And it is not pushing the water it is accelerating a big amount of water without to increase the output pressure. The tail can bee operated with sine wave motion. The sin wave motion is the less effective way to move the tail.

[JonathanCole]

My apologies Kjell, in the pictures the fin appears to be made of metal. What is it made of?

Also if it is flexible and flaps on a shaft, then it would seem that the fin itself would form the shape of a section of the wave that it generates. The travelling wave shape would then be a function of the rate of flapping and the stiffness and length of the fin. Or am I misunderstanding the way your fin is actuated?

[kjell]

You are right.
One of the most important details is the shape and the flexibility of the tail, and the way it is moving.

[C. Gray]

The Hobie Mirage drive is based upon the action of a penguins wings (filppers)as it "flies" underwater. The flexibility of the Mirage propulsors supposedly approximates a screw propeller of proper pitch and diameter as it swings through its 180 degree arc.
That got me to thinking about a similar propulsion set up using pedals to drive a fish tail shaped fin back and forth. Would a fish tail be more effective than a penguins wings...?
Any thoughts on the subject?

[kjell]

The Hobie Mirage drive is a very clever devise. Do to the 180 degree arc the Mirage drive is more efficient than a penguins wings. A fish tail can only make one sweep at the time and the frequency has to bee double than the Mirage drive to bee able to compete.

[jam007]

Found this fotage of flow around a fish fin.
Notice that the thrust is generated by the water flowing from the high pressure side around the aft edge of the fin. In addition to this there exsists a reversed von Kármán street behind the fin.
See ref: Lauder et al (http://darwin.bio.uci.edu/~edrucker/home/Other%20PDFs/Lauder.et.al.ICB.2002.pdf)

[masrapido]

The Hobie Mirage drive is a very clever devise. Do to the 180 degree arc the Mirage drive is more efficient than a penguins wings. A fish tail can only make one sweep at the time and the frequency has to bee double than the Mirage drive to bee able to compete.

So if 180 degrees is more efficient than a fish tail-type of propeller, it would be logical to assume that twice the 180 degrees (360) would be almost as twice efficient, (allowing for losses)? 360 degrees being rotary movement...

[kjell]

Twice the 180 degrees does not means twice efficient,
The main difference between the Mirage fin and a tail fin is that the Mirage fin is making a circular movement and the tail fin is making a linear movement. The water speed is the same on total area on the fin tail and the water speed is different on all parts of the Mirage fin.
The advance of the 180 degree movement is that the cavitation has no time to build up and the AoA can bee more than a propeller. The same happens with a fast moving tail fin.

[jam007]

This seems to be an interesting article: Anderson, J. M., Streitlien, K., Barrett, D. S. and Triantafyllou, M. S. (1998). Oscillating foils of high propulsive efficiency. J. Fluid Mech. 360,41–72.

Have any of you read it? Is it good? I had hoped to read it tomorrow (at the library) but now work has made it impossible but I will read it as soon as I can.

How efficient is a fin? I have found numbers around 40 % in the articles on fish that I have read on the net.
How efficient is a propeller?

[Martijn_vE]

I was part of a project 8 years or so ago, that developed a propulsion system based on the path of tail of a whale through the water, which is a bit similar to a sinus. The propulsion consisted of a 2 vertival wheels with a number of blades (naca profiles) in between. The position of these blades was continiously adapted to follow that tails movements. See http://www.nap.edu/openbook/0309058791/html/946.html or google for whale tail propulsion.

[JonathanCole]

I was part of a project 8 years or so ago, that developed a propulsion system based on the path of tail of a whale through the water, which is a bit similar to a sinus. The propulsion consisted of a 2 vertival wheels with a number of blades (naca profiles) in between. The position of these blades was continiously adapted to follow that tails movements. See http://www.nap.edu/openbook/0309058791/html/946.html or google for whale tail propulsion.

This is a really excellent resource that puts the entire issue into an internally self consistent technological and scientific language and framework. The device described here is very similar to some advanced wind turbines that I have seen. Martijn_vE, what role did you play in this work? Do you mean to say vertical axis wheels? Have vessels been built using this concept?

[yipster]

your the same Martijn van Es right ?
welcome to these forums Martijn !
yipster :cool:

[JonathanCole]

Having read the Proceedings at the link that Martijn pointed us to, I have a few questions about how this thing works. One question relates to the float of the blades. They need an angle of attack so they must not be free floating on the pivot. Yet if they maintain a fixed angle in all portions of the orbit, then they create a lot of unnecessary drag. So the question is, how is the angle of attack controlled? Is it a complex mechanism? I can imagine that it might be advantageous to simply switch from a fixed angle of attack to a free floating pivot.

Another question is calculating the drag induced by the turbulence and wetted area of the two parallel wheels. Another issue is the duct effect if the wheels are solid surfaces. Would this propulsion device work well between the hulls of a 6 meter beam catamaran? The suggestion as to wheel diameter is for 60% of the draft. A 16 by 6 meter catamaran might only have a draft of a meter or less. Will this give enough propulsor surface area to create the desired reduction of loading? I might like to utilize this in the solar electric cat I am designing if it made enough of a difference in efficiency.

[cyclops]

Back to the original post---------Fish tail motions as a replacement for what we use now.-----------I know a fishes sinewave motion is less effecient than a screw propeller. It is constantly accelerating and decelerating and stopping at each end of the sweep, not as effecient as the constant thrust of a screw device. Next topic.------I love fish and eat them.

[yipster]

Martijn, thanks for the article and keep doing it but think i confused you with Emile vE or Martijn S, other crazy dutch guys i had contact with over torpedo propulsion. one had a couple of small submarines and build a turbine is his motorbike, the other build a human diving fishtail suit, a surfboard foilsail he could stand in and what else, does this ring your belll or do i have names and plans mixed up :confused:

[kjell]

[QUOTE=cyclops] I know a fishes sinewave motion is less effecient than a screw propeller. It is constantly accelerating and decelerating and stopping at each end of the sweep, not as effecient as the constant thrust of a screw device. QUOTE]

The limit of propeller efficiency is when the cavitations start.

The tail propulsion don’t have problem with cavitations. In the moment cavitations start on the suction side of the tail, do to the oscillating, this side is converted to pressure side and the cavitations stops. This gives the tail the opportunity to work with more efficiency than a propeller
It is important to understand the way the tail works. You can’t compare the way a propeller accelerate the water with the way the tail accelerate the water. The amount and the speed of water is what producing the forward thrust. The propeller can’t accelerate more water than what the cavitations permits. The efficient tail is not using sinewave motion. Fishes only use sinewave motion at slow speed swimming.

[DMacPherson]

The limit of propeller efficiency is when the cavitations start.

I feel compelled to put in my two cents. I have no issue with the premise that there is merit in a sinusoidal propulsion system, but if it is based on a requirement that the above quote is true, then it will not stand up.

Efficiency really doesn't have anything to do with cavitation - efficiency is the ratio of thrust to torque (or thrust to power, if you prefer). On conventional inboard propellers, excessive cavitation can cause a reduction of both thrust (bad) and required input power (good), and in many cases it will reduce its efficiency where the "bad" loss of thrust is greater than the "good" reduction in input power. However, this is not always the case for all propellers. You just need to find the right propeller for the job.

Super-cavitating propeller designs are meant to operate in a fully-developed vapor cavity, with the majority of its thrust coming from the pressure face, which is unaffected by cavitation. High-performance outboard propellers are a good example of this type of propeller. Many super-cavitating propellers have efficiencies well above 0.60, which is certainly respectable.

So, keep plugging away on the sinusoidal propulsor, but be careful to let it stand on its own merit, not in comparison to some other propulsor type.

Regards,

Don MacPherson
Tech Dir
HydroComp

[JonathanCole]

So, keep plugging away on the sinusoidal propulsor, but be careful to let it stand on its own merit, not in comparison to some other propulsor type.


I hope everyone participating in this thread will take the time to carefully read the article that that Martijn has identified. According to the computer/mathematical model presented, this epicycloidal propulsion device has the potentential to be more efficient than standard props in open water use. Other benefits are also identified. Maybe the assumptions of the model are flawed, but if participants carefully look at the article, then perhaps the reasoning can be critiqued. The last page compares regular props with this whale tail propulsion unit. Actually it is not anything like a whale tail in its form. It is a rotational device with pivoting vertical wings.
http://www.nap.edu/books/0309058791/html/946.html

[cyclops]

Sinewave IS a fish tail in motion. Anything else on this post should be a seperate post. For the fish tail to be eff. it would need a ship hull like a fishbody to feed it smooth undisturbed water. The tail would be of the same proportions on both. NO ship owner would use it. Not enough cargo eff. A fish uses it's tail for getting food or fleeing. Not maximizing cargo capacity. This subject is nonesense to compare the 2 different end uses of each.

[JonathanCole]

Sinewave IS a fish tail in motion. Anything else on this post should be a seperate post. For the fish tail to be eff. it would need a ship hull like a fishbody to feed it smooth undisturbed water. The tail would be of the same proportions on both. NO ship owner would use it. Not enough cargo eff. A fish uses it's tail for getting food or fleeing. Not maximizing cargo capacity. This subject is nonesense to compare the 2 different end uses of each.

Actually, if you take any of these mechanical propulsion systems including a standard prop, they all describe a sine wave or something close to it. if you take a point on a standard prop and project it's location in time, it describes a 3 dimensional helical pattern, which looked at from the side in a 2 dimensional view, is indistinguishable from a wave.

What makes a propellor of any type more or less efficient relates to its ability to maintain laminar flow without shedding a lot of turbulent vortices. Because of the rate of flow over the surface and tortuousness of the path of flow, it would seem to make sense that there may be better solutions than the standard rotary prop. That is what this thread is about from my point of view.

It is a discussion of other approaches that incorporate the mechanisms seen in nature. If you look at the article that Martijn submitted, the device is not really trying to directly emulate nature. It is looking at the mathematics and determining that a thrust generator whose surface moves more slowly through the water, but, which has much greater surface area, may have significant efficiency advantages.

[tspeer]

There's an article in the latest Journal of Ship Research that is relevant to this thread.

Liu, Pengfei, "Propulsinve Performance of a Twin-Rectangular-Foil Propulsor in a Counterphase Oscillation," JSR, Vol 49, N0 3, Sept 2005, pp. 207-215.

Theoretical study using a panel code to compute the thrust and propulsive efficiency of two parallel foils moving toward and away from each other.

They found the two foils produced over 50% more thrust than a single foil oscillated in heave, and at a higher level of efficiency. The thrust coefficient is fairly low, and drops off rapidly when the aspect ratio of the foils drops below 12 for the twin foil. As the foils are oscillated faster, the thrust increases but the efficiency decreases. Same for increasing the amplitude of the oscillations. Placing the foils closer together increases the thrust and efficiency.

Pretty much what you might expect, but they put numbers to it.

[cyclops]

Cheese it. Everyone knows a big area, slow turning ---propellsor of whatever design--- is the most efficent. Tugboats have the highest thrust, per ton of hp. per mph.. If they thought for a split second they could increase thrust Eff. they would have done it by now. They do theory and practical to get any sales advantage.

[waveless]

High-Speed Waveless Sinusoid Propeller

I posted it at boatdesign.net in 08-07-2005, 12:22 PM, and I also post the link to china invent net(www.1st.com.cn).

here is the link:
http://boatdesign.net/forums/showthread.php?t=8340

I already made a model and tested, I do not know how to post my video here.

[JonathanCole]

If they thought for a split second they could increase thrust Eff. they would have done it by now.

Yup, and if God wanted us to fly he would have given us wings. Since he didn't we had to invent it ourselves.:) So I guess its OK with him if we keep on working this problem.

[kjell]

I made some experiments with horizontal tails with good result. This was a R/C rescue devise.

[kjell]

An other experiment with horizontal tail propulsion.

[waveless]

here is my model of sine wave propulsion.

[cyclops]

Your right Jonathan, I am a bit of a realist on projects.

[JonathanCole]

Everyone knows a big area, slow turning ---propellsor of whatever design--- is the most efficent.

Sure, but what if there are also other design requirements for the boat, like shallow draft? There are certainly circumstances that one can imagine that might better utilize a vertical axis thruster device, for example. That is what is described in Martijn's article from the Twenty-First Symposium on Naval Hydrodynamics (1997) Commission on Physical Sciences, Mathematics, and Applications. My guess is that these folks take themselves fairly seriously!!

[waveless]

Hi,

My god tell me that sinewave motion is not as effecient as the constant thrust propulsion. So a new perfect constant thrust propulsion is invented, you will see my new propulsion 'op 7 december tijdens het Nationaal Innovatie Evenement octrooien van TNO' in Utrecht.

[Martijn_vE]

I have a few questions about how this thing works. One question relates to the float of the blades. They need an angle of attack so they must not be free floating on the pivot. Yet if they maintain a fixed angle in all portions of the orbit, then they create a lot of unnecessary drag. So the question is, how is the angle of attack controlled? Is it a complex mechanism?

It's a bit similar to voith schneider propulsion, only in this case the angle of attack of the blades was continously adapted by electronics rather than mechanically if i recall correctly

[Martijn_vE]

Martijn, think i confused you with Emile vE or Martijn S, other crazy dutch guys
Thanks for generous comparison, but no, I'm not one of them.

[masrapido]

Hi,

My god tell me that sinewave motion is not as effecient as the constant thrust propulsion. So a new perfect constant thrust propulsion is invented, you will see my new propulsion 'op 7 december tijdens het Nationaal Innovatie Evenement octrooien van TNO' in Utrecht.

I couldn't have paid for this...now I know what waveless means. as good old Marx said, religion is opium for the masses.

(my buddy waveless is even stealing my words. sinewave "is not as efficient as the constant thrust". I'm going to slap him with copyright laws, made in usa-aca free trade crap, so hard, he's going to discover waves)

:cool:

[waveless]

Masrapido,

I pick up your words on the post, there is nothing copyright.

My water bike is making in china, you will see that is the most efficieny and faster water bike, it will break the speed record of rolling boat.

[masrapido]

best of luck maestro. don't forget us when you become filthy rich, ok? come by sometime, say hello.

[safewalrus]

Apart from the inflated ego's of the main protagonists in this entertainment (got as far as page 4, and had to stop - exhausted!) the main problem I can see from a practical view point is the fact that if the whole boat is "snaking" through the water, you puts yer coffee cup down and bingo! you got coffee all over the the bloody table! Just a thought!

And Masrapido 'tis great to see that your OK buddy, there was some concern (see Open forums) that you might be swimming round the "Mexus/Texico Gulf" great to see that your not!

[masrapido]

was only basking in the glory of the southern sun...

:D

am trying to draw lines of a boat for leisure coastal showing off in full safety of nearby marinas in case winds get naughty.

and taking lessons in tongue control. mi chica is coaching me.

(I am bound to fail...apologies to all, especially the serious and professional ones in this forum)

:rolleyes:

[trouty]

:rolleyes: :p :idea: :D

String Theory? - How long is a piece of string? No matter how long - it won't be long enough, and even if it were it'd get all tangled and you'd do ya quince and cut it all up in a temper anyway!!! :D

Sine Wave, Signs that wave? underwater? - it could work I guess! :)

Broken Symmetry - is the reason for the efficiency of the manta ray propulsion discussed.

Powering it with Plasmoidal induction will make other forms of water propulsion basically redundant, is my best guess.

You could look backk and search for the thread on plasmoidal induction proulsion, and apply it to the problem and voila - it will work.

“Two Nobel prizes were awarded in 1957 for substantiating the process for extracting free Electromagnetic energy from the vacuum, yet not one current Electrical Engineering or Classical Electromagnetics textbook mentions it”

Broken Symmetry
For the open-minded reader, let me explain what broken symmetry means, and what the broken symmetry of a dipole means with respect to powering any dipolar EM circuit.

The strong prediction of broken symmetry by Lee and Yang and its experimental proof by Wu et al. in 1957, initiated a great revolution across physics and won a nearly instant Nobel Prize in December 1957 for Lee and Yang.

One of the broken symmetries proven by Wu et al. and published in 1957 is the broken symmetry of opposite charges, as on the ends of a dipole.

That asymmetry is used by charges and dipoles for extracting and pouring out Electromagnetic energy from the vacuum, yet not one current Electrical Engineering or classical electromagnetics textbook mentions the energy implications of dipolar asymmetry. Nor do they mention that every charge and dipole freely pours out real observable EM energy continuously, with no observable energy input.

Thus the textbooks implicitly assume that all EM fields, potentials, and energy are freely created out of nothing at all by their associated source charges.

Either the conservation of energy law is falsified, or the source charge must be receiving the necessary energy input in virtual state form from the active vacuum.

Broken symmetry essentially means that something virtual (shadowy, but real in a special sense and widely used in physics; it has real physical consequences, since it creates all the forces of nature) has become observable (real in the ordinary everyday sense that it can be detected, measured, observed, and used.). The broken symmetry of the end charges of a dipole rigorously means that, once the charges are forcibly separated to form that dipole, the dipole (its end charges) continuously absorbs virtual (fleeting) photons from the seething vacuum, coherently integrates these "photon pieces" into real observable photons, and re-emits the resulting real EM energy in the form of real observable photons in all directions at the speed of light.

That is not this author's work; that is particle physics as justified by the award of two Nobel Prizes. It isn't even in the electrical engineering model, so no objection based on standard classical EM and electrical engineering concepts has any validity at all.

That's why a dipolar permanent magnet, with opposite magnetic charges on its ends locked in there by the material itself, continuously exhibits magnetic field in the space surrounding it (out to the ends of the universe, if the magnet has been around long enough). There is a continuous and steady stream of EM energy, extracted directly from the vacuum and integrated into observable magnetic field energy, pouring forth from the dipolarity of that magnet. At any external point in that stream, the steady flow will give a steady or "static" reading for the magnetic field and thus for the intensity of the flow at that point.

Actually there is no such thing as a "static" field or potential in the universe; simply check out Whittaker's 1903 decomposition of the "electrostatic" scalar potential into bidirectional longitudinal EM waves, and his 1904 decomposition of any field and wave pattern into two such potentials comprised of bidirectional longitudinal EM waves. The 1904 paper founded what today is known as superpotential theory. The 1903 paper has been largely ignored by the academics, although it has been formidably weaponized by several nations, notably the Russians not long after WW II. Application of Whittaker's 1903 and 1904 papers is responsible for the weapons that then Secretary of Defense Cohen referred to in 1997.


1) (a) T. D. Lee, "Question of Parity Conservation in Weak Interactions," Phys. Rev., 104(1), Oct. 1, 1956, p. 254-259. Errata are given in in Phys. Rev. 106(6), June 15, 1957, p. 1371; (b) T. D. Lee, Reinhard Oehme, and C. N. Yang, "Remarks on Possible Noninvariance under Time Reversal and Charge Conjugation," Phys. Rev., 106(2), 1957, p. 340-345.

2) C. S. Wu, E. Ambler, R. W. Hayward, D. D. Hoppes and R. P. Hudson, "Experimental Test of Parity Conservation in Beta Decay," Phys. Rev., Vol. 105, 1957, p. 1413


I have met the enemy......
And They - is US!

We are the enemy, because we refuse to imagine - and we can't invent what we can't imagine!

Cheers!

[trouty]

it works like this.

http://www.cheniere.org/images/magic%20reordering%20processa.jpg

Cheers!

[jam007]

LOL

Anders M

[masrapido]

And Dr. Nikola Tesla, who invented everything before anyone even thought of anything, described the new energy type he discovered in late 1890's, working for Edison. Later Dr. Tesla proved his theory of the new type of energy by building electric car that was successfully tested by US army and Westinghouse representatives. The car was drawing the energy from the air. There were no batteries in it.

[cyclops]

I will take 2.

[chandler]

Tesla, isn't that a band from Boston??

[chandler]

Wouldn't it be great if all the innovative technology that didn't profit big buisiness{sp} was actually developed?

[trouty]

:?: That it isn't?

Being Developed - that is! :rolleyes:

The proper queston tho is, "Who's developing it and to what use is it being put?".

Another pertinent question might be...

"Why release a new energy development, if you haven't already cornered the market on it?"..

So - just how do you corner the market on a global free enegery source?

If your a Fascist global oil oligarchy, how do you prevent everyone else from no longer needing, what you've spent a few generations creating? (A global oil oligarchy)?.

All good questions! - but 'the answer's could get us all into hot water - probably better not to go there!

Cheers!

[Guillermo]

A simplified propulsive model of bio-mimetic robot fish and its realization (http://journals.cambridge.org/download.php?file=%2FROB%2FROB23_01%2FS0263574704000426a.pdf&code=526e1764b276df7983c2e95bce65491e)

[VladZenin]

Unfortunately this file is not available. [S0263574704000426a.pdf].

[Guillermo]

Go to: http://journals.cambridge.org/action/login
On the right side of the screen there is a search facility: Type there "robot fish" and you'll find the article as the first one in the list that appears.
Cheers.

[VladZenin]

The page you refers to is currently unavailable too. Could you send forward this article to vladimirz@iimetro.com.au please?

[sigurd]

Question from the uneducated peanut gallery: For boat propulsion, what would drive the preference toward either a (or two opposing) stiff high aspect wing, or a flexing unit like a diver's monofin? I was thinking that some of the efficiency gain from a monofin over two fins (used as a monofin) might be due to the longer span that it enables - so why has it not evolved to even higher AR (looks like the high performance models are approx square or atleast very low AR) - and would it be feasible to try and construct a diving fin with a rigid, high AR foil section like a NACA 0010 or whatever?

Kjell mentioned that humans can't kick fast enough to benefit from it - but I don't understand why. The slower crafts (planes, boats) usually benefits from a large span.

Another thing I don't quite get, is that the propulsive area of slow fish are usually bigger than on the very fast fish, in opposite to diving fins. As was mentioned, maybe acceleration and agility has something to do with slow fishes' preference for a large area, but acceleration is not a high priority in many of the watersports where large high speed fins are used.

I have read about the mirage drive that it is less exhausting to use at cruising speed than a kayak oar (it utilises bigger muscles so this isn't a surprise), but that the top speed is less. So why is that? Too large area? Too much flex? Is lack of torsional stiffness in the wings the only thing that sets the AoA in the mirage?

Is the turning point of fins a large loss source, so that amplitude is preferrable to frequency for efficiency? I have read something about insect flying, and there seems to be all sorts of odd, complicated things going on, one of them being the utilisation of vortices to increase lift if I remember correctly - especially the smallest insects I think. Is this relevant to any fish, or manmade oscillating propulsion?

[AleX`G]

Apart from the inflated ego's of the main protagonists in this entertainment (got as far as page 4, and had to stop - exhausted!) the main problem I can see from a practical view point is the fact that if the whole boat is "snaking" through the water, you puts yer coffee cup down and bingo! you got coffee all over the the bloody table! Just a thought!

And Masrapido 'tis great to see that your OK buddy, there was some concern (see Open forums) that you might be swimming round the "Mexus/Texico Gulf" great to see that your not!

Surely if you made the contraption the size of a supertanker the snaking movement would be reduced to a steady sway which you may not notice. Due to the relativly small movements.
I might try some experiments of my own on this subject. Do you think the wave created my the boats in that experiment were cancelled out by destructive interference from the fin.
Sounds like an interesting idea.

[sigurd]

The lauder et al pdf linked in this thread speculates that the bluegill caudal fin benefits (makes more thrust) because of the vortex from the dorsal fin. Wonder what those little protrusions on the aft part of the mackerel are?

" Although the design of thunniform swimmers is optimised for high-speed swimming in calm waters, it is particularly inefficient for other actions such as slow swimming, turning manoeuvres and rapid acceleration from stationary, as well as for turbulent water."

How does the proximity of the surface affect the design of flapping boat propulsors? The flapping (aero) wing paper I once read stated that the opposing flapping wings acted like they were in "surface effect" IIRC. But, from the other side of the surface, in the water, the surface effect is detrimental to lift in all directions? Also would the turbulent surface water give points to the flexible fin over the high AR rigid wing as seen in the "pump-a-bike" or whatever it is called? On a tangent, is proximity to the sea bottom hydrodynamically beneficial for fish?

Specifically also, I am looking for a means to manually drive a singlehanded 20' by 3m cat.
I suppose a propeller would be too drafty if an efficient size is chosen.
Two rowing oars?
A single rowing oar, sitting on one hull with the blade between the hulls?
A pedal, or "mono-pedal" system for flapping a fin (or two opposing fins)up and down?
Somewhere some time I read that if you put a horizontal foil on the bow, wave action and pitch resonance of the vessel could drive the vessel forward against the sea and wind. Is this bollicks?

[sigurd]

sorry, not "pump-a-bike" - it's called a trampofoil :)

http://ourworld.compuserve.com/homepages/roberthodgen/tramp.htm