Resistance Estimation

Hi,

I recently started browsing your forum. It seems you have some pretty good discussions.

Anyway, I noticed a thread where someone asked: "Are there any plans to include resistance estimates based on physics (e.g. thin ship theory, Kelvin-Neumann, Neumann-Stokes)as opposed to empirical methods (e.g. Holtrop Delft, etc)? If so, will your product be able to handle multihull resistance?"

Well, I made a program last weekend in excel which uses Michell's equation for calculating thin-ship upright resistance. (and checks it with the Delft series).

It only takes inputs of disp, cp, lcb, lcf, awp... and generates a generic form. It's very slow, and not intuitive either. However, I just made it in one weekend to see if I could do it.

Anyway, if you are interested, you can get the file at: (warning - dynamic ip address...)
http://redcoopers.servebeer.com/
and then go to "Michell's equation"

I most likely will never update the file again, but if you have any questions, feel free to shoot me an email.

Note: if you use Excel XP, you may have to lower your security level since the spreadsheet uses a lot of VBA. I promise I don't have any viruses!

Nice forum, by the way!
-Jon

 

Agree... Does anyone have an easy to use software to estimate resistance and power for boats. I`m particularly interested in savistkys method...

 

Thanks for providing another version of Michell's integral, however I am not sure that your method gives correct results for transom sterns. Michell's integral usually requires special treatment for such vessels.

All the best for the New Year!

Leo.

 

The same for you Leo!, I would like to take this opportunity just to ask you some questions about michlet, do you have planned to have a version that can perform resistance figures for boats with L/B ratios in the 2-4 range, for displacement boats, I asked you once about it, I just want to know if you have plans do something like this, and if you are going to have a code for seakeeping, thanks, and have a great one.

 

Dear Guest,
Thanks for giving me the opportunity to prattle on about my own work.

MICHLET
At this stage I have no plans to extend Michlet to hulls with L/B less than about 6 because thin-ship theory is not very accurate for such hulls. Incidentally, "thin" in this context does not mean that a hull must be like a knife blade, but rather that the longitudinal slope of the hull be small. (A convenient way to think of it is that thin-ship theory is Ok for hulls with semi-circular cross-sections, but not for semi-circular waterlines.)

Transom sterns are a special case: the longitudinal slope is certainly not small (it is approx. 90 degrees) but this difficulty can be circumvented by a careful integration by parts of a variant of Michell's integral. Michlet uses some other special terms to improve correlation with experiments at low Froude numbers.

Unfortunately not many users of Michlet purchased the program so there hasn't been much incentive to update it lately. The main change in version 8.05 will be to add a better viscous drag estimate because I believe that the ITTC 1957 correlation line has had its day. In particular, it is not a good estimator of viscous drag at low Reynolds numbers typical of towing tank models and other small vessels.

SHIP MOTIONS
I have several programs that can calculate ship motions as well as wave resistance, viscous resistance, and wave patterns of monohulls. A demo version will be available from ww.cyberiad.net sometime after I return from holidays in mid-January. That version will accept (the US Navy's) SMP input files and will produce standard SMP output as well as estimates of wave resistance and viscous resistance. I will not be able to supply manuals for the original SMP but these can be purchased from NIST for a small fee.

Leo.