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 Boat Design Forums Michlet, L/B B/T ratio limits

#1
03-21-2012, 03:10 PM
 Godofredo Join Date: Mar 2012 Rep: 10 Posts: 4 Location: Concepcion,Chile
Michlet, L/B B/T ratio limits

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
#2
03-21-2012, 09:42 PM
 Leo Lazauskas Senior Member Join Date: Jan 2002 Rep: 1934 Posts: 1,850 Location: Adelaide, South Australia
Quote:
 Originally Posted by Godofredo 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
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.
#3
03-22-2012, 04:38 AM
 daiquiri Engineering and Design Join Date: May 2004 Rep: 2981 Posts: 3,497 Location: Italy (Garda Lake) and Croatia (Istria)
Quote:
 Originally Posted by Leo Lazauskas See for example the thesis by Simon Robards to see how thin-ship theory compares with experiments for a very large variety of hulls.
Thanks for the tip Leo.
Your link let me to an error page, but this one works: http://www.unsworks.unsw.edu.au/prim...=unsworks_3426

Cheers
#4
03-22-2012, 04:49 AM
 Leo Lazauskas Senior Member Join Date: Jan 2002 Rep: 1934 Posts: 1,850 Location: Adelaide, South Australia
Quote:
 Originally Posted by daiquiri Thanks for the tip Leo. Your link let me to an error page, but this one works: http://www.unsworks.unsw.edu.au/prim...=unsworks_3426 Cheers
Thanks, Slavi. I guess they have shuffled stuff in their library again!

Even if you ignore the predictions used in the thesis, the experimental results
are quite valuable to have on hand.