Michlet 9.32 Released

[Leo Lazauskas]

I am aware that this is not the ideal tool to model the very high length to beam planing catamarans that we are considering for our project. Problem is that there is little out there to do estimates for this hull with. Are there considerations other then the correct rise out of the water and trim that need to be considered that Michlet does not account for in its computations. If that is all that is missing we can get estimates by mixing methods for finding the rise and trim of our boat and entering that information into Michlet.

UNO Prof. Bill Vorus and his then student Taravella were looking into planing
hulls a few years ago.
Taravella. Brandon M. and Vorus, William S.,
"A general solution to low-aspect-ratio flat-ship theory"
J. Engineering Mathematics,
Vol. 71, 2011, pp. 171-184.

Ask your supervisor if their codes are available to be used.

Are there considerations other then the correct rise out of the water and trim that need to be considered that Michlet does not account for in its computations.

Transom stern flows are difficult for most codes.
Michlet does not calculate any near-field effects, so the pressure on the
hull does not enter into predictions. That is a big deficiency.

Does Michlet recalculate the center of buoyancy for each angle of trim as the boat trims?

Yes. Look at the 4th column of the "ship_output_by_speed.mlt" file.

I'm a little uncomfortable with trim as large as +/- 5 degrees.

One good check would be to use a body with an exact surface area and
volume and try different trim and sinkage to compare to Michlet's
calculations.
A sphere is not a good example because it is too unlike a hull. A
better choice, and closer to your planing hulls, would be a parablic
strut with a fairly shallow draft.

 

[JacobSimon]

UNO Prof. Bill Vorus and his then student Taravella were looking into planing
hulls a few years ago.
Taravella. Brandon M. and Vorus, William S.,
"A general solution to low-aspect-ratio flat-ship theory"
J. Engineering Mathematics,
Vol. 71, 2011, pp. 171-184.

Its funny you should mention Dr. Taravella. He is actually one of my professors here. I have talked to him about using Vorus'es code and that will probably be the direction that we eventually go but since he just got his hands on the catamaran version of the code he has not had a chance to learn it yet. My team was looking for a way to do a comparative study between a planing hull and a semi planing wave piercing hull form for our project before we actually try and get any hard numbers on resistance.

It is amazing that the world of ship hydro is so small. I keep seeing familiar names like Tom Speers, Vorus, Brandon, and yours everywhere I look.

Thank you for your help so far. We will figure something out.

 

[Leo Lazauskas]

Its funny you should mention Dr. Taravella. He is actually one of my professors here. I have talked to him about using Vorus'es code and that will probably be the direction that we eventually go but since he just got his hands on the catamaran version of the code he has not had a chance to learn it yet. My team was looking for a way to do a comparative study between a planing hull and a semi planing wave piercing hull form for our project before we actually try and get any hard numbers on resistance.

It is amazing that the world of ship hydro is so small. I keep seeing familiar names like Tom Speers, Vorus, Brandon, and yours everywhere I look.

Thank you for your help so far. We will figure something out.

I'm surprised that your group hasn't tried dumping the problem into a
CFD code and letting it do the work.

We were working on simpler formulations for slender planing hulls, but then
Tuck became very ill and died in 2009 which left the work unfinished. See:

Tuck, E.O.,
"Slender Planing Surfaces"
Journal of Engineering Mathematics, 58 (2007) 289-299.
http://www.maths.adelaide.edu.au/yvonne.stokes/Tuck/pdfiles/casling06.pdf

 

[oldsailor7]

That E.O.Tuck paper is very interesting, as it covers the mathematical theory of the design of a pair of water skis.
Arthur Piver took this to heart in his design of the Frolic trimaran.
He simply took the dimensions of a pair of water skis, enlarged them and added sides to them.
These then formed the amas of a small trimaran with the limiting factor of trail ability (or even car top transport,- american cars were very big in those days).
As a result the overall beam of the 16ft Frolic was 8ft. A B/L ratio of 50%.
As modern Tris are 70% or even more, that was pretty narrow, but the Frolic was a great little performer. Ask Jim Brown. He scooted all over SF bay on one

 

[fallguy]

Yes. I know this thread is out of date. I tried to find Michlet, but am unable to do so. Any sign of the developer? Google wasn't much help in a cursory look.

 

[fallguy]

answering my own question, Michlet is not hosted externally, but found a zip file here

Michlet 9.33 Released https://www.boatdesign.net/threads/michlet-9-33-released.52865/

 

[rxcomposite]

Leo's article can be downloaded from his universty site. Cyberiad.???. I forgot the file extension. Could be au since it is in Australia.

Look for Optimum Spacing of a Family of Multihull and Solar Powered Multihull. Lots of data and illustration.

Though the article covers only elliptical and wiggly hulls, the Michlet carries an NPL type hull sample. A semi displacement hull similar to yours. Might work although yours is more of a planing cat similar to the second image I posted earlier in another thread.