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  #1  
Old 05-06-2012, 07:22 PM
Quartz Quartz is offline
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Submarines vs whales vs fish: are propellors more efficient than flukes or tails?

Submarines have propellors; whales have flukes; fish have tails. Which is the most efficient? And what about quietest and least-easy to detect?

(I'm not sure if there are any fish large enough to really count, even if you include the whale shark.)
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  #2  
Old 05-06-2012, 08:02 PM
kanicbird kanicbird is offline
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Originally Posted by Quartz View Post
Submarines have propellors; whales have flukes; fish have tails. Which is the most efficient? And what about quietest and least-easy to detect?

(I'm not sure if there are any fish large enough to really count, even if you include the whale shark.)
I thought penguins were the most efficient.

Last edited by kanicbird; 05-06-2012 at 08:04 PM..
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  #3  
Old 05-06-2012, 09:01 PM
Chronos Chronos is offline
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I'd expect flukes and fishtails to be about equivalent, since they're basically the same thing, just turned on its side.

As for either versus propellers, it depends on what the thing they're driving is. A flexible-tailed submarine would be an engineering nightmare, and likewise a free-spinning propeller would be an evolutionary nightmare.
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  #4  
Old 05-06-2012, 09:36 PM
Quartz Quartz is offline
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Originally Posted by Chronos View Post
As for either versus propellers, it depends on what the thing they're driving is.
Are we not able to measure the noise, energy, and other efficiencies of a whale's fluke?

Quote:
A flexible-tailed submarine would be an engineering nightmare
That's for another thread.
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  #5  
Old 05-07-2012, 08:24 PM
Hail Ants Hail Ants is offline
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I've watched several PBS shows where some college puts on a challenge to design a better sub propulsion system. Invariably many entries feature some form of mechanical fin or flipper. At one of them a Navy egghead basically dismissed all of these entries as fancifully impractical, that it's been proven long ago that a rotating propeller is by far the most efficient marine propulsion method.

It's similar to the wheel. No life form has evolved one, but on a reasonably smooth surface its the best transportation system.
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  #6  
Old 05-07-2012, 08:29 PM
Gagundathar Gagundathar is offline
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Originally Posted by kanicbird View Post
I thought penguins were the most efficient.
Maybe so, but they are absolutely the coolest things in the ocean.
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  #7  
Old 05-07-2012, 08:35 PM
Whack-a-Mole Whack-a-Mole is offline
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Modern submarines, I have read, are dead silent. Often described as black holes in the water.

Mind you this is due to high tech design of propellers. I have a recollection of (I think Toshiba) getting into deep doo-doo in the 80's because they sold hi-tech milling equipment to the Soviets which would allow them to manufacture silent propellers.

Most propellers cavitate when spinning (they form little bubbles along the edges of the propeller which implode and make sound). Flukes and tails do not do this...whether the design prevents it or merely because they do not churn water as fast as a propeller does I have no idea (I am guessing the latter). A spinning propeller moves much faster causing the bubbles (hence noise).

Super hi-tech submarine propellers these days do not do that. Or rather I should say are a lot less prone to it. IIRC if the sub goes to full power there is a point where there is no avoiding it. If you watch the movie Hunt for Red October there is a scene where the American captain tells the helmsman to go to full speed. The sonar operator complains they are cavitating (making noise). Of course the captain knows this and it was his intent to make the noise to let the other sub know they were there. Till that though the other sub had no clue the US sub was near them. Movie I know but accurate as far as it goes for that bit.
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Old 05-07-2012, 11:41 PM
DHMO DHMO is offline
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I have heard that when Tom Clancy was writing the book, The Hunt for Red October, he used publicly-known "Popular Science"-type information about state-of-the-art modern submarine design, and extrapolated and filled in the blanks some.

His information on top-secret propulsion technologies hit a little too close to home, some government agents came to see him, and he had a bit of 'splainin to do before they were satisfied that he had no access to restricted information.
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Old 05-08-2012, 12:11 AM
Whack-a-Mole Whack-a-Mole is offline
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Originally Posted by DHMO View Post
I have heard that when Tom Clancy was writing the book, The Hunt for Red October, he used publicly-known "Popular Science"-type information about state-of-the-art modern submarine design, and extrapolated and filled in the blanks some.

His information on top-secret propulsion technologies hit a little too close to home, some government agents came to see him, and he had a bit of 'splainin to do before they were satisfied that he had no access to restricted information.
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.
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  #10  
Old 05-08-2012, 12:20 AM
t-bonham@scc.net t-bonham@scc.net is offline
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Originally Posted by Hail Ants View Post
At one of them a Navy egghead basically dismissed all of these entries as fancifully impractical, that it's been proven long ago that a rotating propeller is by far the most efficient marine propulsion method.
This was true for airplanes, too, until jet engines were developed. Could a marine jet be designed the same way, to be more efficient? I believe there are marine animals that move by jets rather than tails or flukes (squid, for example).
Quote:
Originally Posted by Hail Ants View Post
It's similar to the wheel. No life form has evolved one,
I believe there are microscopic life forms (protozoans?) that have evolved a wheel form of propulsion.
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  #11  
Old 05-08-2012, 12:37 AM
Gary T Gary T is offline
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Quote:
Originally Posted by t-bonham@scc.net View Post
I believe there are microscopic life forms (protozoans?) that have evolved a wheel form of propulsion.
Perhaps you're thinking of propeller-type propulsion? As I recall flagellates are known to whip their tails around in a circular motion, effecting a crude propeller.
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  #12  
Old 05-08-2012, 12:42 AM
Gary T Gary T is offline
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Quote:
Originally Posted by t-bonham@scc.net View Post
Could a marine jet be designed the same way, to be more efficient? I believe there are marine animals that move by jets rather than tails or flukes (squid, for example).
Significantly different, I'd say. Aircraft jets provide constant thrust, with (if I'm not mistaken) the intake air providing oxygen for combustion. Doing that with water is a whole 'nother proposition. Squid do it one squirt at a time via muscular contraction; I suspect a mechanism to do that would be terribly unwieldy.
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  #13  
Old 05-08-2012, 04:20 AM
DSeid DSeid is online now
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Dolphins have a propulsive efficiency of 0.81. Not sure what propulsive efficiency subs have.

If you want a detailed explanation of the differences between swimming modes in fish read this. Short version pertinent to the op:
Quote:
Thunniform mode is the most efficient locomotion mode
evolved in the aquatic environment, where thrust is generated
by the lift-based method, allowing high cruising speeds to be
maintained for long periods. It is considered a culminating
point in the evolution of swimming designs, as it is found
among varied groups of vertebrates (teleost fish, sharks, and
marine mammals) that have each evolved under different
circumstances. In teleost fish, thunniform mode is encountered
in scombrids, such as the tuna and the mackerel. Significant
lateral movements occur only at the caudal fin (that produces
more than 90% of the thrust) and at the area near the narrow
peduncle. The body is well streamlined to significantly reduce
pressure drag, while the caudal fin is stiff and high, with a
crescent-moon shape often referred to as lunate [Fig. 7(d)].
Despite the power of the caudal thrusts, the body shape and
mass distribution ensure that the recoil forces are effectively
minimized and very little sideslipping is induced. The design
of thunniform swimmers is optimized for high-speed swimming in calm waters and is not well-suited to other actions such
as slow swimming, turning maneuvers, and rapid acceleration
from stationary and turbulent water (streams, tidal rips, etc.)
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  #14  
Old 05-08-2012, 04:59 AM
Dr. Strangelove Dr. Strangelove is offline
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Originally Posted by Gary T View Post
Perhaps you're thinking of propeller-type propulsion? As I recall flagellates are known to whip their tails around in a circular motion, effecting a crude propeller.
They don't just whip around in a circular motion--they actually rotate on an axle. Hard to imagine the same principle working on a large animal, though.
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  #15  
Old 05-08-2012, 05:25 AM
DSeid DSeid is online now
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A relevant article:
Quote:
Do fish and jellyfish swim better than submarines? It depends a lot on what you mean by ‘better’. Some people have argued that fish are more efficient than subs, meaning that they waste a smaller fraction of the total propulsive energy. Others have argued that efficiency isn't all that important; instead, it's just the total energy that matters, regardless of what fraction of it is wasted.

One major difference is that jellyfish and fish produce thrust in pulses, whereas propellers on submarines produce thrust more or less continuously.

There's good reason to suppose that pulsed propulsion (jellyfish) might be more efficient than steady jets (propellers). For example, pulses produce vortex rings, which tend to pull in extra fluid because of their rotation, resulting in a jet that's effectively larger than an equivalent steady jet. But pulses may also take more energy to produce. ...

... the group found that pulsed propulsion was almost always 20–40% more efficient than the baseline steady jet. At low pulse rates, though, the energy saved through increased efficiency didn't make up for the extra energy required to spin the ring to make the pulsed jet. But at high pulse rates, the group saw an overall energy saving.

So jellyfish, and maybe also fish or biomimetic submarines with flapping fins, may in fact swim better than subs, but only if they're clever about how they produce their pulses.
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  #16  
Old 05-08-2012, 07:47 AM
si_blakely si_blakely is offline
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Originally Posted by t-bonham@scc.net View Post
This was true for airplanes, too, until jet engines were developed. Could a marine jet be designed the same way, to be more efficient?
The Russians have a supercavitating rocket torpedo - 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
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  #17  
Old 05-08-2012, 08:53 AM
Xema Xema is offline
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Originally Posted by t-bonham@scc.net View Post
This was true for airplanes, too, until jet engines were developed.
Jet engines are generally less efficient than recip engines with props. Indeed, attempts to make jet engines more efficient often entail high bypass ratios (basically, the jet engine incorporates blades that move air, like propellors).

In many cases the blades are inside a cowling; in some, they are unducted.
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  #18  
Old 05-08-2012, 09:09 AM
Sailboat Sailboat is offline
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Originally Posted by Whack-a-Mole View Post
Mind you this is due to high tech design of propellers. I have a recollection of (I think Toshiba) getting into deep doo-doo in the 80's because they sold hi-tech milling equipment to the Soviets which would allow them to manufacture silent propellers.
A thumbnail description from Wikipedia:

Quote:
In 1987, Tocibai Machine, a subsidiary of Toshiba, was accused of illegally selling CNC milling machines used to produce very quiet submarine propellers to the Soviet Union in violation of the CoCom agreement, an international embargo on certain countries to COMECON countries. The Toshiba-Kongsberg scandal involved a subsidiary of Toshiba and the Norwegian company Kongsberg Vaapenfabrikk. The incident strained relations between the United States and Japan, and resulted in the arrest and prosecution of two senior executives, as well as the imposition of sanctions on the company by both countries.[5] The US had always relied on the fact that the Soviets had noisy boats, so technology that would make the USSR's submarines harder to detect created a significant threat to America's security. Senator John Heinz of Pennsylvania said "What Toshiba and Kongsberg did was ransom the security of the United States for $517 million."
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  #19  
Old 05-08-2012, 10:10 AM
TriPolar TriPolar is online now
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There's a lot more difference between a fish and a submarine than flukes and propellors. And efficiency has different definitions. Fish (and fish like mammals) are more maneuverable than submarines, and power themselves by consuming other fish and plants in the sea. They have flexible bodies made out of stuff like meat and bones, not rigid metal. The effectiveness of their propulsion is based on their entire body shape, not just the shape of their flukes and fins. Some studies indicate their skin contributes to laminar flow reducing drag. OTOH submarines have torpedos, which even way cool fish don't have.

ETA: Also fish don't implode if they spring a leak. Though they kind of explode if they're rapidly depressurized.

Last edited by TriPolar; 05-08-2012 at 10:11 AM..
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  #20  
Old 05-08-2012, 10:54 AM
Philster Philster is offline
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Jet-type propulsion in boats:

Jets have been used to jet water to power boats and Waverunners, but be wary of the results, because jet boats will show worse fuel economy and top speeds, because the props on boats intended to plane also create lift, resulting in less wetted hull (less resistance).

Jet boats don't get this lift, so to do an apples to apples test, you need to power some non-planing hulls (displacement hulls) with jets and compare to displacement hulls with props.

.
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  #21  
Old 05-08-2012, 11:31 AM
Gray Ghost Gray Ghost is offline
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Adding another article 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:
Quote:
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.
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  #22  
Old 05-08-2012, 11:58 AM
MikeF MikeF is offline
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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.
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  #23  
Old 05-08-2012, 12:16 PM
Gagundathar Gagundathar is offline
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Quote:
Originally Posted by Whack-a-Mole View Post
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 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)".
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  #24  
Old 05-08-2012, 12:41 PM
kanicbird kanicbird is offline
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Originally Posted by si_blakely View Post
The Russians have a supercavitating rocket torpedo - 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.
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  #25  
Old 05-08-2012, 01:27 PM
Gagundathar Gagundathar is offline
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Originally Posted by kanicbird View Post
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/supe...hesis_eric.pdf
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  #26  
Old 05-08-2012, 01:36 PM
TriPolar TriPolar is online now
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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.
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Old 05-08-2012, 02:10 PM
Gray Ghost Gray Ghost is offline
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Quote:
Originally Posted by TriPolar View Post
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 of the 1970s? Examples in modern navies include the Norwegian Skjold class MTB/corvette and the Russian Bora-class corvette. I confess to being hazy as to the exact difference between an SES and a hovercraft.
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  #28  
Old 05-08-2012, 02:55 PM
TriPolar TriPolar is online now
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Looks like air cavity systems are close. I was wondering about something that produced the cavity through cavitation caused by the specially shaped nose.
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  #29  
Old 05-08-2012, 03:33 PM
mlees mlees is online now
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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?
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  #30  
Old 05-08-2012, 03:57 PM
Mangetout Mangetout is offline
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Quote:
Originally Posted by mlees View Post
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) would probably be a closer analogue to a fish tail.

Last edited by Mangetout; 05-08-2012 at 04:00 PM..
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  #31  
Old 05-08-2012, 04:03 PM
Quartz Quartz is offline
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Originally Posted by mlees View Post
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.
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  #32  
Old 05-08-2012, 04:16 PM
mlees mlees is online now
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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.
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  #33  
Old 05-08-2012, 06:51 PM
ralph124c ralph124c is offline
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What About Rear Paddle Wheels?

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.
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  #34  
Old 05-09-2012, 07:06 AM
Der Trihs Der Trihs is offline
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Originally Posted by Xema View Post
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.
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  #35  
Old 05-09-2012, 09:10 AM
kanicbird kanicbird is offline
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Originally Posted by ralph124c View Post
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.
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