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Author Topic:   Shark Week on Discovery
jward posted 08-13-2001 10:10 AM ET (US)   Profile for jward   Send Email to jward  
I was watching shark week last night when they mentioned that the roughness of a sharks skin enabled it to travel through the water more efficiently (I always wondered why they were not slick or slimy). In fact they stated the US submarines have adapted the use of a rough surface on the exterior of the hulls in order to make them more efficient. It was also mentioned that some racing yachts also use a rough surface on the bottom of the hull. Does anyone know the science behind this? Is anybody out there using this technique on their Whaler?
SuburbanBoy posted 08-13-2001 10:30 AM ET (US)     Profile for SuburbanBoy  Send Email to SuburbanBoy     
Thanks for your update, now I can return all of the paint remover I was going to use on my mottled bottom paint!


Bigshot posted 08-13-2001 10:43 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I have heard 2 different opinions on smooth bottoms. 1 is if you wax(slimy)the water beads like a car hood and the air bubbles slow you down. 2 is waxed bottoms are more efficient. I believe in the do not wax theory because it saves me time.
Makonut posted 08-13-2001 11:04 AM ET (US)     Profile for Makonut  Send Email to Makonut     
the micro-turbulence engendered by water friction is decreased when it remains confined in the grooves of sharks (skin)..same theory should apply to boats..keep in mind a sharks "skin" is like your beard..smooth toward your tail (bone) and rough toward your head. Isn't mother nature a genius? :)


LarrySherman posted 08-13-2001 11:18 AM ET (US)     Profile for LarrySherman  Send Email to LarrySherman     
The whole purpose is to increase laminar flow, and reduce turbulant flow. On experiment on subs used the "goo gun," which squirted viscious goo out of the bow of the sub to increase top end speed. There was a news report in June of a Russian rocket propelled torpedo which used the same technology.

Very cool stuff.

Whalerdan posted 08-13-2001 11:53 AM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     
BS - Air bubbles slow you down? Try running through water, then run through air. Which is easier? Easier means less friction, which in turn means faster. But I like your no wax theory for the same reasons you stated.

hauptjm posted 08-13-2001 12:12 PM ET (US)     Profile for hauptjm    
Water beading on a waxed surface is created by friction. Ergo, waxing below the waterline is creating undue friction. Racing sailors will use nothing but one of two methods for finishing below the waterline: wetsanding and teflon. A lot are wetsanding their teflon applications.

In all of the one design racing I've done over the last 30+ years, I've never seen a race decided by the boat's wetted surface. Of course, no one will deny that they'll do whatever is necessary to win or gain an advantage, and still be legal.

Whalerdan posted 08-13-2001 01:20 PM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     
I always though water beads on a car because of the surface tension of the water is stronger than the friction between the water the surface. I don't think that there could be much friction between the water and the surface when I recall how quickly the water runs off the surface when you drive down the road.
Techmage posted 07-02-2003 01:25 PM ET (US)     Profile for Techmage  Send Email to Techmage     
"I always though water beads on a car because of the surface tension of the water is stronger than the friction between the water the surface."

This is correct. as to a rough surface haveing less friction, that is not true. A sharks skin is faster not because it is rough, but because of its particular SHAPE. Water molecules moveing against other water molecules have less friction that against MOST other surfaces. Therefore if a surfaces SHAPE promotes water to adhere to it instead of traveling along it or pushing against it, then the MOVEING water is traveling along a "skin" of water and not the object itself.

jaccoserv posted 07-02-2003 03:02 PM ET (US)     Profile for jaccoserv  Send Email to jaccoserv     
Do you guys remember the last summer olympics? All of the swimmers, male and female traded in their speedos for "sharksuits" that looked like overalls. The idea was that the rougher skin grabbed the water better, they also scuff up their hands on the cement before diving in, and shave their body hair right before a race so as too leave their skin rough. Now I can understand why a swimmer would want the rough surfaces to push hrough the water but I can't understand why a rougher boat bottom would increase speed.

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