# Lift onset, planing, and lift coefficient

Discussion in 'Hydrodynamics and Aerodynamics' started by sandhammaren05, Aug 13, 2018.

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### sandhammaren05Senior Member

New paper posted on lift onset with planing defined. Delta wing-type lift coefficient provided in agreement with Clements' data on v-bottoms.

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### Mr EfficiencySenior Member

What the hell is a "finite transom", used several times in the discussion ?

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### sandhammaren05Senior Member

The hell finite transom is finite beam.

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### Mr EfficiencySenior Member

Are there boats that don't have finite beam ?

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### latestarterSenior Member

I think they are referring to the analysis, with a theoretical infinitely wide surface there is no lateral flow so easy to calculate, with a finite beam it is much more difficult to calculate the real world position.

"A 1950s era discussion of planing as lift (Du Cane[9])is based on a back of the envelope calculation that predicts a lift coefficient proportional to cos α , with finite lift at no attack angle. This is wrong.
Lift must vanish as α goes to zero. The calculation is based purely on leading edge spray for a boat of infinite beam (two dimensional flow), neglecting the side spray and waves that are the main cause of lift-reduction and drag."

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### sandhammaren05Senior Member

Are you asking 'are there boats that do not have a finite beam at the transom, where the transon meets the bottom? Yes, plenty of them.

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### sandhammaren05Senior Member

DuCane assumed 2D flow with no Kutta condition and got a lift coefficient that makes no sense
(see the end of the paper) because it remains finite as trim angle vanishes. I treat only 3D flow.

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### Mr EfficiencySenior Member

Maybe there is a language or translation confusion here.

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### Mr EfficiencySenior Member

A theoretical convenience ? Maybe so.

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### sandhammaren05Senior Member

You should not be confused. Look at fig. 1 and 2.

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### sandhammaren05Senior Member

No, clearly defined. Again, see figures 1 and 2.

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### Mr EfficiencySenior Member

No, I'm not confused, just wondered about the usefulness of talking about finite beam transoms.

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### DCockeySenior Member

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### sandhammaren05Senior Member

Outdated by my posted ms above.

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### sandhammaren05Senior Member

Good thing to think about because that's the key to lift and planing.

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