# Michlet, L/B B/T ratio limits

Discussion in 'Hydrodynamics and Aerodynamics' started by Godofredo, Mar 21, 2012.

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### GodofredoNew Member

I am a newcomer to this forum, so if this post has been covered before, my excuses. But it is impossible to cover everything to find out.
Michlet is mainly thought for slender hulls, that is waht I have read about it. But I have not seen any practical information about the limits regarding L/B and B/T. I just discovered this wonderful effort, but I know that there are limits. I do not want to be calculating the resistance of a vessel that is out of limits of the theory and math of the software.
Does anyone has an idea?
Is there any rule of thumb to (always) keep in mind about the limits of Michlet?
Regards

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### Leo LazauskasSenior Member

The main restriction is that the longitudinal slope should be small.
I would not rely on estimates of Michlet for L/B < 7. You might be able to
use it for smaller values, but you will need to also use some form of
empirical correction. See for example the thesis by Simon Robards to see
how thin-ship theory compares with experiments for a very large variety
of hulls.

Robards, Simon William, "The hydrodynamics of high-speed transom-stern vessels"
http://unsworks.unsw.edu.au/vital/ac.../unsworks:3426
Appendix D contains the resistance graphs.

Thin-ship theory should be able to order hulls correctly in terms of
resistance for lower L/B. For example, if thin-ship theory says that hull A
has less resistance than hull B, then that will usually also be the same
for experimental results. The actual drag might be in error, but the order will
be correct. The same is also usually true for many CFD predictions.

Good luck!
Leo.

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### daiquiriEngineering and Design

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