Sine wave propulsion

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.

 

Aloha and peace to you,

Jon

 

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.

 

Thanks Jonathan.

 

Let's move on

Masrapido,

1. This is how the world understands what sculling is:
[font=arial,sans-serif][size=-1][size=+0]scull[/size] [/size][/font](skl)
[size=-1]NOUN: [/size]<>A long oar used at the stern of a boat and moved from side to side to propel the boat forward....
[size=-1][/size][size=-1]VERB: [/size]
[size=-1]tr. [/size]To propel (a boat) with a scull or a pair of sculls. [size=-1]
VERB: [/size]
[size=-1]intr.[/size]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

 

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.

 

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

 

More info on sculling

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

Yoav

 

I 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.

 

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.

 

(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.

 

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. "

 

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.