Displacement Hull Speed of a Tuna

[naturewaterboy]

What have we learned about boat hull design from studying how fish swim?

[Raggi_Thor]

Submarines and airplanes are easier to design than boats. They operate in just one medium and you don't have to consider wave making (as long as you are in sub sonic speed).

[yotphix]

Nothing from fish but this from dolphins! (hope i uploaded that right)

[yotphix]

i think that's right

[naturewaterboy]

So why not put a big fish shaped hull under the boat (and make it wiggle like a fish) and stick a boat on top of it out of the water?

[MikeJohns]

Keith

If you have ever watched salmon running up a fall or race they get up on the surface of the water and drive with their tails cause they can't swim against the current submerged. A bit like a planing power boat. They would benefit from an inboard engine and a jet drive

Seriously though we have little to learn from fish for surface craft and earlier hullforms based roughly on fish shapes were less than ideal resistance wise.

We can improve on most fish shapes for submerged vehicles. However even optimised shapes are far less efficient than surface craft due to a big wetted surface drag penalty, also operating so close to the surface would also add a substantial surface wave.

Cheers

[Raggi_Thor]

Originally Posted by naturewaterboy

So why not put a big fish shaped hull under the boat (and make it wiggle like a fish) and stick a boat on top of it out of the water?

Search for SWAT :-)

[Robert Gainer]

And yet we have a lot to learn from the surface of the dolphin. The skin has a texture and flexibility that enhances speed without adding the need for power. I have often thought that a hull with flexible bladders to change the shape and built of dolphin skin would be great. Imagine a sailboat that had a lifting foil shape that changed on each tack. No leeway at all. Or a hull that had the ideal PC for all speeds.
Robert Gainer

[MikeJohns]

Originally Posted by Raggi_Thor

Search for SWAT :-)

SWATH is stability oriented definately not for speed.

[MikeJohns]

Originally Posted by Robert Gainer

And yet we have a lot to learn from the surface of the dolphin. The skin has a texture .......................Imagine a sailboat that had a lifting foil shape that changed on each tack...........

I read that they appear to detect and prevent seperation keeping laminar flow and consequently low drag.
I really doubt that we can use their technology which ultimately is very complex and consequently very hard to make durable reliable and affordable.

Twin lifting keels/daggerboards angled for windward lift work well too.

Cheers

[marshmat]

Originally Posted by naturewaterboy

What have we learned about boat hull design from studying how fish swim?

That we really can't duplicate it.
A boat has to carry load, and a submarine has to maintain an atmosphere inside it. Fish don't carry loads and they adapt to ambient pressure. Fish have hundreds of muscles behind a flexible skin, and can bend and flex as they please; human-made materials tend to prefer rigidity. Fish have some interesting techniques, but they're solutions to a very different problem than that of the boatbuilder.

[Raggi_Thor]

Originally Posted by Robert Gainer

Imagine a sailboat that had a lifting foil shape that changed on each tack. No leeway at all...

I think this is a popular misunderstanding.
Why do you want "no leeway"?

[Robert Gainer]

Raggi_Thor,
It was my understanding that to prevent sliding sideways a keel or other surface was added to the hull. This worked by have an angle of attack which generated lift and drag. If you used a lifting surface to prevent leeway and it didn’t have the same amount of drag then more energy goes to making progress. Leeway is just a waste when you are trying to work to windward but it’s the drag I was really trying to reduce. Maybe not the best choices of words but you get the idea.
Robert Gainer

[yipster]

Originally Posted by MikeJohns

SWATH is stability oriented definately not for speed.

i only half agree, stability yes and not high speed but think u-boats and check navy swaths, they are way over their hullspeed

[Excalibur]

In regards to SWATH hulls... If you design the underwater body to get the CG as low as possible and maybe add a ballasted keel, could you get enough stability to go to a monohull? Its true that such a design would have very limited deck area, but if one was williing to put up with that in return for a high displacement speed, would it work?