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Topic: Sharks, What we can learn from them...< Next Oldest | Next Newest >
Capn Jimbo Offline
The Godfisher




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Posted: Dec. 04 2007,17:17

Is smoother faster?  Survey sez - No!  Another myth busted?

Some sharks are faster than others, and researchers wonder why for good reason.  If they can determine why, they may be able to increase the speed and lower the fuel costs signficantly.

So far it's all about "denticles".  

Denticles are actually small scales and the fast shark's version are smaller than the slower species.  The smaller denticles are actually raised for speed - scientists are studying how these raised scales affect the boundary layer in such a way as to reduce drag.

It is counterintuitive, as most of us believe that  the smoother the surface the faster the kayak.  



:capn:
ps. for further info, google Dr. Amy Lang, University of Alabama, boundry layer control...


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stant01 Offline
Cuda




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Posted: Jan. 31 2008,09:16

The speeds attained by marine animals have long been a puzzle.  "Gray's paradox" refers to the speeds attained by dolphins.  Gray's research, done in the 1930's, said that dolphins (one of the fastest marine animals) should require 10 times as much power as they can actually produce to reach their sprint speeds of around 20 mph.  He postulated that the flexibility of the dolphin skin suppressed turbulence.  Gray's work was later shown to be flawed, but his basic paradox remains, and the latest "blip" I have seen on the puzzle was some research done in Japan that claimed that dolphins shed skin flakes which suppress eddies.  Maybe.   We'll see if this idea holds up.

In any case, I'd be reluctant to apply shark skin research to my kayak.  I'll still try to keep it as slick and smooth as possible.  An awful lot of tow tank research stands behind that idea.  :p
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Scupper Pro Frank Offline
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Posted: Feb. 02 2008,16:45

WELL, JIM, FLAWED OR NOT, THE ORIGINAL DOLPHIN HYPOTHESES & RESEARCH

and what's more recently followed it argue for boundary layer turbulence and eddies reducing straight/smooth surface laminar flow frictions and subsequently decreasing drag.

Navy's been keenly interested in such stuff for same reasons you stated in initial post, plus, for marine warcraft, speed tends to reduce kills on the receiving end, increase on the giving end, and in particular, these principles are eagerly sought by the submarine engineering community.

Tank testing notwithstanding, I'll go with recent trends in research.

Which is fine, I suppose.  

Only problem is, US/Pentagon/Navy can spend gazillions underwriting research, practical R&D, and, eventually, if successful, expensive tooling to actually get a 'skin crawling' boat out there.

Doubt we kayakers -kayak designers, manufacturers, seller -could even imagine coming close...  And us kayak users...???  Where would we get the money to pay for such innovation?

And when all was said & done, for us kayakers, would any improvement be significant?  At what cost?  And even more important than being a significant improvement -would it be an important (i.e., meaningful) one?

I don't ever think we'll see the day when such innovations are -a la Popular Mechanics of the 1950s-style -incorporated into our everyday kayak hull materials design, so we might as well -for the time being, and a LONG time after -just


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krash Offline
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Posted: Feb. 03 2008,19:34

They been using shark skin reasearch for years trying to develop faster skin-suit's for olympic swimmers and runners.

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stant01 Offline
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Posted: Feb. 04 2008,07:46

True, Krash.  And for Olympic-caliber bicyclists as well. But the advantages of these skinsuits are in a few seconds out of an hour, or tenths of a second out of minutes.  I think I agree with Scupper Pro Frank - not significant in real world fishing.

Speaking of which, I need a fishing "fix".  White bass beginning to run here in central Texas - see y'all!
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Kayak Jeff Offline
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Posted: Feb. 04 2008,11:29

You know we don't have to go to the Navy for info on this. Laminar flow reduction technology and research has been around for quite some time in racing sailboats and that technology is beginning to spill over to kayak manufacturers. Some boats that I have gotten in recently from NZ and GB have a "rough" textured molded into the hull. I have heard the most America's Cup boats have the equivalent of a 600 grit surface.
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krash Offline
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Posted: Feb. 04 2008,13:05

Nuke Subs, but I did not tell ya that.

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critterdog Offline
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Posted: Feb. 04 2008,14:11

Love the white bass. My favorite time is at night under lights, during a mayfly hatch. You can catch non stop, on fly or ultra lite.

  You should see the bottom my kayak, it's well textured.I think it goes faster everytime I use it.


Edited by critterdog on Feb. 04 2008,14:14
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stant01 Offline
Cuda




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Posted: Feb. 06 2008,14:28

If anyone wants to learn lots more about this stuff, go to Wikipedia and search on "boundary layer".  That will be a good start, and leads to lots of other links. Like why a dimpled golf ball flies much farther than a smooth one.  But why a dimpled airfoil is generally slower than a smooth one.  Boundary layer turbulators, trip wires, and all that good stuff.  Don't go glassy-eyed over the Navier-Stokes equations; just read the text, which is generally pretty good.  Though talking about "bubbles" in air instead of eddies or vortices makes me think some parts of it were translated from German, or maybe Japanese...:D

Best available research says that unless your kayak is aalive and flexible like shark or porpoise skin, least drag would be produced by making it smooth (smooth enough to keep all projections within the boundary layer) until the point on the hull where boundary layer separation occurs.  (Where is that?  WAG says probably somewhere aft of the widest point on the hull.)  Then put on a rough strip or ridge to make the boundary layer go turbulent, so it remains attached longer.

Too complicated for me; like Frank, I'll just
Paddle On.
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8 replies since Dec. 04 2007,17:17 < Next Oldest | Next Newest >

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