wave lenght by Michlet

[pavel915]

is it possible to find the wave length of transverse wave system so that i can see whether my ship is operating in displacement or planning region for a particular speed?
If yes, then how?

[Leo Lazauskas]

Originally Posted by pavel915

is it possible to find the wave length of transverse wave system so that i can see whether my ship is operating in displacement or planning region for a particular speed?
If yes, then how?

The wavelength of "pure" transverse waves is

Lambda = (2 * pi * U^2)/g

where

U = ship speed
g = gravity

This wavelength, however, does not tell you anything about whether a hull is, or is not, in "planing" mode. You have to find some other method.

All the best,
Leo.

[pavel915]

Thanks Leo for your reply,
Actually i knew the equation you have written,
But i am confused that, does not the wave length depend on the hull form at all? For any kind of hull the wave lengh will be equal to ships lenght at Froude number 1/Square-root(2Xpi) ?

[Leo Lazauskas]

Originally Posted by pavel915

But i am confused that, does not the wave length depend on the hull form at all? For any kind of hull the wave lengh will be equal to ships lenght at Froude number 1/Square-root(2Xpi) ?

Yes, the wavelength very close to the hull is affected by the shape of the hull. But you asked about the wavelength in Michlet.

Michlet results are only valid behind the hull, i.e. it only calculates far-field waves using linear wave theory. In that case, the wavelength of pure transverse waves in deep water is given by the equation I gave previously.

To see the separate near-field and far-field components see, for example, the SWPE report at:
http://www.cyberiad.net/library/pdf/tsl00a.pdf

Leo.


Leo.

[pavel915]

Thanks Leo,
I get it now,

[gonzo]

You are overthinking the problem. A planing hull is running over the bow wave. The wave has the lenght of the boat's waterline.

[Leo Lazauskas]

Originally Posted by gonzo

You are overthinking the problem. A planing hull is running over the bow wave. The wave has the lenght of the boat's waterline.

And you have grossly under-thought the problem

Displacement boats can operate at a Froude number where the wavelength is exactly same as the boat length. And planing hulls at exactly the same Froude number may not actually be planing.

Cheers,
Leo.

[pavel915]

Actually i was trying to talk about the highest speed upto which a displacement boat should operate,(may be called transition between displacement and semi-displacement) i.e. where the wave length is equal to the boats lenght. But i was confused about whether this wavelength depends on the hull form or not,
Leo has made this clear to me,

[gonzo]

The wave length depends on the waterline length. However, the hull shape can have different waterline lenghts at different speeds. This is used to advantage on sailboats.

[Leo Lazauskas]

Originally Posted by gonzo

The wave length depends on the waterline length.

Not in Michlet.

The wavelength of the transverse wave system is given by the equation I gave earlier. Hull length does not appear in that equation.

Leo.

[terhohalme]

Gonzo, no

I ask you to repeat your tank tests.