planing theory

Peasant- and ox-powered, more likely.
It is funny that Newton was right, just for the wrong type of flow.

I hate to think what the world would be like if he hadn't had that
remarkable year and a bit away from London. As someone said, he could
have written a brilliant essay on "What I did in my Holidays".

However, if he had just got things right in a couple of places, and people
didn't perpetuate the errors, things might be more advanced.

 

It is not I nor anyone else for that matter that is offended. Unless you feel vexed for being asked to explain your rationale further?

Which sums it up.

And confirmed by the childish immature negative hits points I received for daring to ask questions. QED I'm afraid. The person unable to debate, hides in the corner lashing out in the safety of their anonimity...jessss....so much for advancement and

Agreed. However,

I'm sorry if you feel this way Tom, but there is no "pissing" as such going on. If you wish to make bold statements that fly in the face of accepted theorems then you need to support them as does anyone else. Unless you feel you are the exception

 

Too bad if someone gave you negative hits ad hoc. Rest assured that it was not me although it seems "someone" docked me. There is more to say I guess, but I've decided to call it quits and anyone can assign any reason for that they wish to.

 

The no-slip boundary condition is necessary because of viscosity; no-slip means that the object is wet, the first layer of fluid sticks to the object's surface. That's the origin of boundary layers and drag, not to mention lift on a foil. I want to focus on the discussion, planing, not on something like 'stretching' that has nothing to do with planing. I don't know if the paper you mention is correct, I haven't worked through it. It's certainly not applicable to this discussion.

Savitsky's paper is old, largely empirical, has little theory. Here's a recent reference that starts from the Navier-Stokes eqns.:

'Hydrodynamics of High-Speed Marine Vehicles', Odd Faltinsen, Cambridge, 2005.

An interesting part of Savitsky's paper is his discussion where porpoising can be expected.

Another participant in this discussion mentioned 'superposition' as an engineering principle. Hydrodynamics is nonlinear, superposition fails except in extreme approximations (creeping flow, vortices in the nonviscous limit).

Frankly, I don't see why peas, beans, or some outdated speculation by Newton was introduced here. The Navier-Stokes eqns' have been around for a long time, and are the correct generalization of Newtonian mechanics to fluids down to the Kolmogorov length scale.

 

You still don't get it. I only gave the reference because you seemed to
imply that the no-slip condition was the only one in use in boundary layer research.

More than that. In response to Breslin's questions he wrote "There is
nothing more to do in planing. I have done it all". That annoyed and
inspired Breslin to pursue his own methods.
(personal comm. between J.P. Breslin and E.O. Tuck, 2001).

Great reference. I hope he spells my name correctly in the next edition

Nor do I.

 

Look like iterations are starting to converge...

 

Ok, thanks for the ref. How is your name mispelled in Faltinsen? I was
mainly interested in that book through trying to understand how to a correct version of Crouch's formula, mainly trying to see how if anyone had even formulated the problem (I had a discussion with BB about that), but nothing about that in Faltinsen.

 

I was just being a jerk. He gets it right in most places, but wrong once on p. 122.

 

Can you really blame 'im??

Oh shoot..now I'm being a jerk, aren't i?

 

So he does!!

I see mine misspelt several times in ref's too...oh well

 

No. I get lost halfway too sometimes.

Back on-topic, sort of...

Trying to estimate the wetted area in the pre-planing (but "splashy") regime
must be a nuisance.
Do you use the grid method discussed in another thread for that too?

 

I wouldn't bet on it. About the Froude nr. or, as one pundit on this site wrote, the Freud nr. Assuming that speed V goes like the sq. rt. of length L, L^1/2, looks wrong and even silly. The speed goes up as wetted length decreases, not the reverse. So the right way to say it is that, the higher the speed, the less wetted area, and therefore the higher the Freud nr.

 

The simple hull-length-based Froude number is not appropriate.
Shouldn't you use Fr based on wetted length?

 

I'm only thinking of wetted area, which is minimal for a racing boat.

 

The way I see it, is that if the wetted area is small because the wetted
length is short, then the correct Fr should be based on wetted length.
Moreover, the flow tends towards 2D as the wetted width becomes greater
than wetted length.

Of course, you can use a full 3D CFD code to get whatever you want.