# How to deal with truncated transome?

DELFTship forum Hydrostatics and stability How to deal with truncated transome?

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• #36086

Participant

I have a question about truncated waterlines. In computing Cp, can one use imaginary extension of waterlines of the healed hull in order to compute true value of Cp? The picture should explain my question. I do understand that there is a discrepancy in this, but what is more wrong:

(a) compute Cp with truncated waterline (and get distorted hull’s shape Cp) or
(b) compute Cp with imaginary waterlines (and get an hydraulics error and get more proper shape for computational purposes)?

Thank you all for your help.

• #36089
Eric Bailey
Participant

I don’ know if my experience covers this situation but – wouldn’t using imaginary waterlines where the hull is not – give you imaginary coefficients?

I take it upright the hull DWL ends just before the hull does? Is there a reason not to extend the hull? You would get a little better flow I would think…

Also, I wonder if the heeled coefficient thing is a new fangled idea coming from designing in a computer? I never bothered with it back when I designed a couple power boats manually… of course they were power boats…

I am really curious to see what others think of this – good luck.

Eric

• #36092
Becker
Participant

Hi all,

it is a interesting question.

In my opinion it is not really a problem wich length and Displacement you use for prism. coeff.
Think about the question: How do you use these coefficients.

Most time you just want to compare quite similar hulls.

On the other hand, with your vitual hull, you get a bigger length and a bigger Displacement. Mainframe section keep quite the same cp will not vary very much.

A quite similar discussion is about Froude numbers. Wich length do you take for froude number….
For comparing similar hulls, it is only important that you always take the same length.

Greetings, William