# Submarines vs whales vs fish: are propellors more efficient than flukes or tails? **URL:** \ **Category:** Factual Questions\ **Created:** [May 7, 2012, 12:22am UTC](https://boards.straightdope.com/t/submarines-vs-whales-vs-fish-are-propellors-more-efficient-than-flukes-or-tails/621111 "2012-05-07T00:22:56Z")\ **Posts on this page:** 15\ **Page:** 2
**Author:** ![Gray\_Ghost](https://avatars.discourse-cdn.com/v4/letter/g/c0e974/32.png) [@Gray\_Ghost](https://boards.straightdope.com/u/Gray_Ghost)\ **Post date:** [May 8, 2012, 4:31pm UTC](https://boards.straightdope.com/t/submarines-vs-whales-vs-fish-are-propellors-more-efficient-than-flukes-or-tails/621111/21 "2012-05-08T16:31:57Z")
Adding another [article](http://www.bluefish.org/jettuna.htm) to the pile; this one about a research team examining the role that the fish’s body plays in interacting with and generating vortices that increase propulsion efficiency. In the particular velocity regime they were interested in, they found that fins were more efficient that propellers: > [@](#): > > By multiplying the width of an object’s wake by the frequency with which vortices form inside it, then dividing the result by the speed of the flow, the Strouhal number gives a measure of how fast vortices are being created and how close together they are. > > Working with Mark Grosenbaugh, a marine engineer at the Woods Hole Oceanographic Institution in Massachusetts, the researchers decided to apply the equation to swimming fish. They adapted the Strouhal number to express the frequency of tail swishes multiplied by the width of the jet, with the product divided by the fish’s forward speed. Then they retreated to their lab and flapped their foils at a range of speeds and amplitudes. Measuring the results and refining the combinations, they found that the foils moved the most water using the least amount of energy when the Strouhal number was between 0.25 and 0.35. In that range, their fabricated fishtails delivered efficiencies of up to 86 per cent, compared with a maximum of about 80 per cent for the peak efficiency of ships’ propellers. Later, they discovered that most fish swim within that same range-far above the 0.1 or less that the Triantafyllous’ earlier foils had struggled to achieve. I suspect the answer to “which is more efficient” is going to depend a whole lot on how you set up the problem. Anyway, there’s a few cites within the article for further reading. I vaguely remember in the past, that Discover had an article talking about fins vs propellers and legs vs wheels. I can’t seem to google it up, but IIRC, they mentioned the fins trumping propellers but that wheels were much more efficient than legs. ---
**Author:** ![MikeF](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@MikeF](https://boards.straightdope.com/u/MikeF)\ **Post date:** [May 8, 2012, 4:58pm UTC](https://boards.straightdope.com/t/submarines-vs-whales-vs-fish-are-propellors-more-efficient-than-flukes-or-tails/621111/22 "2012-05-08T16:58:10Z")
There was a news story just yesterday about a submarine propulsion system being developed inspired by the jellyfish. But that’s all they would say. No details at all. ---
**Author:** ![Gagundathar](https://avatars.discourse-cdn.com/v4/letter/g/a183cd/32.png) [@Gagundathar](https://boards.straightdope.com/u/Gagundathar)\ **Post date:** [May 8, 2012, 5:16pm UTC](https://boards.straightdope.com/t/submarines-vs-whales-vs-fish-are-propellors-more-efficient-than-flukes-or-tails/621111/23 "2012-05-08T17:16:45Z")
> [@Whack-a-Mole](#): > > I forget the exact story but supposedly during WWII some story was published in a sci-fi magazine describing a bomb remarkably similar to an atomic bomb. > > As I recall the government freaked a bit and had people investigate. They realized it was just someone’s creative imagination and figured it would seem odd if the stories (the story was a serial) suddenly stopped for no good reason so allowed them to continue. H. G. Wells predicted the atomic bomb in his 1914 essay, _The World Set Free_. He even coined the term ‘atomic bomb’. This isn’t the guy you were referencing in your post, but I thought it was interesting enough to extend the minor hijack. According to this article, [Deadline](http://en.wikipedia.org/wiki/Deadline_(science_fiction_story)) was written by Cleve Cartmill in 1944. It shows up in the March 1944 issue of Astounding Stories. And yes, apparently “[f]earing a security breach, the FBI began an investigation into Cartmill, Campbell and some of their acquaintances (including Isaac Asimov and Robert A. Heinlein)”. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [May 8, 2012, 5:41pm UTC](https://boards.straightdope.com/t/submarines-vs-whales-vs-fish-are-propellors-more-efficient-than-flukes-or-tails/621111/24 "2012-05-08T17:41:41Z")
> [@si\_blakely](#): > > The Russians have a [supercavitating rocket torpedo](http://en.wikipedia.org/wiki/VA-111_Shkval) - it goes fast enough that the cavitation bubble from the (specially designed) nosecone extends over the whole torpedo (with some small control vanes extending out into the water for steering). There is minimal surface friction, so it more efficient, but it has to go 200+ knots to do it. > > Si This is not really supercavating, much of the gas bubble is from rerouted gas exhaust (as stated in the link). Still a nifty idea. ---
**Author:** ![Gagundathar](https://avatars.discourse-cdn.com/v4/letter/g/a183cd/32.png) [@Gagundathar](https://boards.straightdope.com/u/Gagundathar)\ **Post date:** [May 8, 2012, 6:27pm UTC](https://boards.straightdope.com/t/submarines-vs-whales-vs-fish-are-propellors-more-efficient-than-flukes-or-tails/621111/25 "2012-05-08T18:27:41Z")
> [@kanicbird](#): > > This is not really supercavating, much of the gas bubble is from rerouted gas exhaust (as stated in the link). Still a nifty idea. The source of the gas bubble doesn’t seem to matter. "…supercavitating vehicles can achieve high velocities by virtue of reduced drag via a cavitation bubble generated at the nose of the vehicle such that the skin fraction drag is drastically reduced. Depending on the type and shape of the supercavitating vehicle under consideration, the overall drag coefficient can be reduced by an order of magnitude compared to a fully-wetted vehicle. " - [http://www.aem.umn.edu/research/supercavitation/documents/thesis\_eric.pdf](http://www.aem.umn.edu/research/supercavitation/documents/thesis_eric.pdf) ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [May 8, 2012, 6:36pm UTC](https://boards.straightdope.com/t/submarines-vs-whales-vs-fish-are-propellors-more-efficient-than-flukes-or-tails/621111/26 "2012-05-08T18:36:49Z")
The supercavitating article was very interesting and led to an article about supercavitating propellors which was also interesting because it referenced partially submerged propellors which are more efficient than submerged propellors. But is there actually a way to use the supercavitating torpedo design in a partially submerged craft like a boat? Could their be a gas ‘bubble’ that completely seperates a boat hull from the water? Sort of a running indentation in the water surface maybe. ---
**Author:** ![Gray\_Ghost](https://avatars.discourse-cdn.com/v4/letter/g/c0e974/32.png) [@Gray\_Ghost](https://boards.straightdope.com/u/Gray_Ghost)\ **Post date:** [May 8, 2012, 7:10pm UTC](https://boards.straightdope.com/t/submarines-vs-whales-vs-fish-are-propellors-more-efficient-than-flukes-or-tails/621111/27 "2012-05-08T19:10:03Z")
> [@TriPolar](#): > > The supercavitating article was very interesting and led to an article about supercavitating propellors which was also interesting because it referenced partially submerged propellors which are more efficient than submerged propellors. But is there actually a way to use the supercavitating torpedo design in a partially submerged craft like a boat? Could their be a gas ‘bubble’ that completely seperates a boat hull from the water? Sort of a running indentation in the water surface maybe. Something like the [Surface Effect Ships](http://en.wikipedia.org/wiki/Surface_effect_ship) of the 1970s? Examples in modern navies include the [Norwegian _Skjold_ class MTB/corvette](http://en.wikipedia.org/wiki/Skjold_class_patrol_boat) and the [Russian _Bora_-class corvette](http://en.wikipedia.org/wiki/Bora_Class_guided_missile_hovercraft). I confess to being hazy as to the exact difference between an SES and a hovercraft. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [May 8, 2012, 7:55pm UTC](https://boards.straightdope.com/t/submarines-vs-whales-vs-fish-are-propellors-more-efficient-than-flukes-or-tails/621111/28 "2012-05-08T19:55:39Z")
Looks like [air cavity systems](http://orbitalvector.com/Aquatic/Air%20Cavity%20Hulls/AIR%20CAVITY%20HULLS.htm)are close. I was wondering about something that produced the cavity through cavitation caused by the specially shaped nose. ---
**Author:** ![mlees](https://avatars.discourse-cdn.com/v4/letter/m/ba8739/32.png) [@mlees](https://boards.straightdope.com/u/mlees)\ **Post date:** [May 8, 2012, 8:33pm UTC](https://boards.straightdope.com/t/submarines-vs-whales-vs-fish-are-propellors-more-efficient-than-flukes-or-tails/621111/29 "2012-05-08T20:33:19Z")
Would a paddlewheel be considered an analogue to a fish fluke? In March of 1845, the Royal Navy conducted some tests, with the screw Frigate _HMS Rattler_ competing against a paddlesteamer _HMS Alecto_. _Rattler_ won, but I don’t know how accurate of a test that was, as the _Rattler_ may have had bigger (more horsepower) engines. Is that test usefull for this discussion? ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [May 8, 2012, 8:57pm UTC](https://boards.straightdope.com/t/submarines-vs-whales-vs-fish-are-propellors-more-efficient-than-flukes-or-tails/621111/30 "2012-05-08T20:57:56Z")
> [@mlees](#): > > Would a paddlewheel be considered an analogue to a fish fluke? Not really - a paddle wheel is just a variation on a pair of conventional rowing oars. Analogous to the pectoral fins of some fish, I guess. A yuloh (single oar commonly seen on the back of Chinese boats like [this](http://www.youtube.com/watch?v=UjyE7dyR2X4)) would probably be a closer analogue to a fish tail. ---
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [May 8, 2012, 9:03pm UTC](https://boards.straightdope.com/t/submarines-vs-whales-vs-fish-are-propellors-more-efficient-than-flukes-or-tails/621111/31 "2012-05-08T21:03:32Z")
> [@mlees](#): > > Would a paddlewheel be considered an analogue to a fish fluke? I don’t think so, because flukes can generate thrust on both the up and down strokes, BICBW. ---
**Author:** ![mlees](https://avatars.discourse-cdn.com/v4/letter/m/ba8739/32.png) [@mlees](https://boards.straightdope.com/u/mlees)\ **Post date:** [May 8, 2012, 9:16pm UTC](https://boards.straightdope.com/t/submarines-vs-whales-vs-fish-are-propellors-more-efficient-than-flukes-or-tails/621111/32 "2012-05-08T21:16:52Z")
Paddlewheels are cylinders, and while a single paddle may spent more than half of it’s time out of the water (and not producing thrust), there is always one or more paddles on that cylinder in the water at any one time… Ah well. I tried. 🙂 ---
**Author:** ![ralph124c](https://avatars.discourse-cdn.com/v4/letter/r/8797f3/32.png) [@ralph124c](https://boards.straightdope.com/u/ralph124c)\ **Post date:** [May 8, 2012, 11:51pm UTC](https://boards.straightdope.com/t/submarines-vs-whales-vs-fish-are-propellors-more-efficient-than-flukes-or-tails/621111/33 "2012-05-08T23:51:06Z")
I know that propellers are very efficient, but what about the big rear paddle wheels? These were used up to the present day-Mississippi steamers using paddle wheels were made up to the 1930’s. Of course, a river steamship has different requirements from an ocean going ship…and a paddle wheel may be less prone to damage in shallow water. ---
**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\ **Post date:** [May 9, 2012, 12:06pm UTC](https://boards.straightdope.com/t/submarines-vs-whales-vs-fish-are-propellors-more-efficient-than-flukes-or-tails/621111/34 "2012-05-09T12:06:45Z")
> [@Xema](#): > > Jet engines are generally less efficient than recip engines with props. IIRC, the basic principle is that moving a small amount of air (or water, I presume) quickly is less efficient but produces higher thrust; while moving a large mass of air slowly is most efficient. Therefore jets are less energy efficient that props, while in turn props are less efficient than the wings of the plane. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [May 9, 2012, 2:10pm UTC](https://boards.straightdope.com/t/submarines-vs-whales-vs-fish-are-propellors-more-efficient-than-flukes-or-tails/621111/35 "2012-05-09T14:10:57Z")
> [@ralph124c](#): > > I know that propellers are very efficient, but what about the big rear paddle wheels? > These were used up to the present day-Mississippi steamers using paddle wheels were made up to the 1930’s. > Of course, a river steamship has different requirements from an ocean going ship..and a paddle wheel may be less prone to damage in shallow water. I don’t believe they are that efficient. I did a senior project to construct a underwater vehicle and did some research on props. Typically they are about 50% (about 50% of the engine hp is transferred to the water, the other 50% never is produced by the engine). Also the most efficient prop configuration would be a single blade, though for balance a dual blade is the most efficient practical set up. The more blades the less efficiency though the more power you can transmit so more thrust. The reason for the loss of efficiency for more blades is that the blades are passing through the propwash of the others. Props can be made more efficient but they are a compromise to operate over a speed range and load range. A variable pitch prop could compensate and deliver higher efficiencies. With the above posting that a dolphin efficiency at .81 I’d say that nature has a efficiency advantage which may be quite significant. My money is still on the penguin however. [Previous page](https://boards.straightdope.com/t/submarines-vs-whales-vs-fish-are-propellors-more-efficient-than-flukes-or-tails/621111.md?page=1)