fish- designed for speed | SouthernPaddler.com

fish- designed for speed

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jdupre'

Well-Known Member
Sep 9, 2007
2,327
40
South Louisiana
I broached this subject a while back with a couple of guys on the back channels.

Our human powered boats are fairly slow. You can put a complete novice in a good kayak, and in a couple of hours he might be paddling 5mph maximum speed. An experienced kayaker in the same boat might max out at maybe 7-8 mph. Top world crew athletes might be in the neighborhood of 15 mph. This is with the advantage of the long waterline of a 40' boat. Theoretically, the longer the waterline , the faster the top speed.

So, how do you explain a 3' long tuna( short waterline length) swimming 45 mph with that pissant little tail. Their is something else at work there besides strength and streamlining.

World class rowing athletes would kill for a 1% speed improvement. Tuna have a 300% advantage over a world class rowing crew and a 600% advantage over a good kayaker!!

Seems to me, if we could decipher the secret, it would dramatically change our sport.

Just thinking.

Joey
 
W

Wannabe

Well-Known Member
Apr 5, 2007
2,645
2
on the bank of Trinity Bay
Speed=expended energy=work=not going to do it. But the more effecient the hull the less energy it would take to do what little I'm going to do. I'm going to hush now so the more scientifical folk can give you a more sensible answer. Interesting question.
Bob
 
H

hairymick

Well-Known Member
Dec 8, 2005
2,107
2
Queensland, Australia
Joey,

Have a look at the shape and body mass of that fish, all desgned with one purpose in mind, to drive that pissant little tail - hard.

Virtually all the body except for the head is one big mass of streamlined muscle.

Paddlers, on the other hand were not built to propell themselves through water. We rely on relatively small muscle groups, arms backs and shoulders to drive a paddle which, in turn, attempts to pull a relatively inefficient hull shape through the water.

Tuna do what God created them to do. We adapt and do the best we can in an environment that we were never designed for, nor intended to be in. :D
 
B

bearridge

Well-Known Member
Mar 9, 2005
3,092
4
way down yonder
I bet Ron will be buildin' a fish next. Likely take him longer.....mebbe 7-10 days. :wink: The High Sheriff iz built fer speed.....well, hiz head iz bald. :mrgreen:

I am bearridge 'n I approve this message.
 
J

jdupre'

Well-Known Member
Sep 9, 2007
2,327
40
South Louisiana
Mick, I understand the streamlining thing, but 600% better? There's got to be something else. I read that the slime on a fish's body helps and the way the tail reduces the vortex of the tail through the water. I just wonder if we could discover another 20-30% improvement somewhere.
 
J

Jimmy W

Well-Known Member
May 1, 2006
611
1
north georgia, USA
A fin type drive system along the lines of the Hobie Mirage drive or that of the Tailboat at http://www.tailboats.com should beat using a paddle. But a tuna isn't propelled only by the tail, the entire body flexes in wave forms and is also providing thrust not just drag as in a solid boat. I remember reading once that the tiny tooth like structures on shark's skin help to reduce boundary layer drag and a fishes scales might also do that. But as Mick pointed out the fact that most of the mass is muscle producing power is probably the largest factor. That enables at tuna to flex its body and tail for 4 to 5 tail-beats per second which is beyond the abilities of us humans.
http://jeb.biologists.org/cgi/reprint/192/1/45.pdf
Jimmy
 
T

Too Busy

Well-Known Member
Apr 1, 2008
68
0
Summerville, SC
I like to play with water bottle rockets and I ran across a really good series produced by NASA
Here's a webpage that explains a lot about drag.
http://www.grc.nasa.gov/WWW/K-12/airplane/shaped.html

Note the airfoil or "fish shape has le lowest drag coefficient of any of the prismatic solids. Scroll down and click "NEXT" on the factors that affect drag. More surface area means more drag, but since most of us are in the 200 pounds and up range and we want to float on top of the water we need lots of submerged area.

We paddle displacement hulls, so we like a long waterline to give a higher maximum teoretical hull speed based on the bow wave we can overcome.
In general for us longer and skinnier are easier to paddle... otherwise we'd all be paddling a simple box built from 1 sheet of plywood. :wink:
 
A

a Bald Cypress

Well-Known Member
May 7, 2007
577
0
80
Northwest Louisiana
f

OK What about this.

You build a boat that is long and watertight. Make it so when you and your gear are in it, it will submerge to a certain distance.

You will be sitting in the boat with just the "coaming tower" like a submarine out of the water.

That also is an elongated form to reduce resistance.

With the whole hull , or nearly the whole thing, under the water, will the flow pattern allow you more speed ?


Inquireing minds and wierd thoughts want to know.
 
R

rpecot

Well-Known Member
Nov 10, 2006
406
0
Katy, TX
a Bald Cypress said:
With the whole hull , or nearly the whole thing, under the water, will the flow pattern allow you more speed ?
Click to expand...
I say: "No."

You will have more wetted surface area leading to more drag. The idea behind the long, narrow hull is that you have less displaced water to move out of the way than a short, fat boat of the same displacement.
 
N

nolafolk

Member
Jul 19, 2008
6
0
Alabama
Area and drag

A boat has to displace all the water in it's cross sectional area. Shape is very important, but not as important as the amount of water you have to move out of the way. Longer water line implies you can skim on top of the water instead of pushing it to the sides.

Fish can certainly swim fast, but I think that's a combination of nature's design and lots of muscle. If you ever go salt water fishing see how badly you can get beat up by, say, a 30 pound dorado after it's landed. Human beings are puny by comparison.
 
R

rpecot

Well-Known Member
Nov 10, 2006
406
0
Katy, TX
Re: Area and drag

nolafolk said:
A boat has to displace all the water in it's cross sectional area. Shape is very important, but not as important as the amount of water you have to move out of the way. Longer water line implies you can skim on top of the water instead of pushing it to the sides.
Click to expand...
Glad to see my former mentor agrees with me. :lol:
 
J

Jimmy W

Well-Known Member
May 1, 2006
611
1
north georgia, USA
Re: f

a Bald Cypress said:
With the whole hull , or nearly the whole thing, under the water, will the flow pattern allow you more speed ?
Click to expand...

That is an interesting question. I have read that modern submarines are faster submerged than they are on the surface, but they are designed to operate submerged. My feeling is that given the same power and displacement a surface boat could be faster even with displacement hulls on each.
 
J

jdupre'

Well-Known Member
Sep 9, 2007
2,327
40
South Louisiana
I've done quite a bit of research on this subject. It seems that craft traveling through surface water benefit from the swede form and craft traveling fully below the surface do better with the fish form.

But, let's put this in perspective. A 100 meter runner in top form runs less than 25mph. One half of one mile an hour seperates the first place and last place. If someone would come along with a 600% increase in speed (25mph x600%= 150mph) there would be chaos in the sports world.

I know it's a combination of strength and natures's design, but I want to find out what part of that design can be duplicated in our watercraft.

It's just one of my many quirks. :? :D
 
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