Michelet questions

[Yacht Skipper]

Hello,

I'm investigating the resistance of a few hulls options for a 90 feet Sailing Cats.

1. Does Michelet analyse the underbody with the appendages ?
Does it take in consideration the foiled dagger board lift and drag ?

2. I designed the hulls in Maxsurf, how do I export to Michelet ?

Thanks in advance

Mat

[marshmat]

Hi Mat,

The hull in Michlet is defined as a table of offsets, a length, a displacement volume and a draught. As long as you can get your hull geometry in the form of a suitable table of offsets, Michlet can read the hull. Note that it is quite picky about many things- must have an odd number of stations and waterlines, the co-ordinate system is defined in a particular way, etc.

Maxsurf's Hullspeed module may be an easier bet for you, since it interfaces directly with the Maxsurf file.

Michlet calculates the resistance and the wave-making characteristics of the hull when it is moving in a straight line, on an even keel. If you include a keel in the offsets, it will see that as part of the hull. Michlet will not compute trim and sinkage for you, nor will it compute lift and drag on a foil. If you want to analyze a craft with daggerboards in Michlet, I would suggest that you will have an easier time analyzing the canoe body with Michlet and the rudders and daggerboards separately, in a program designed for foils.

[Yacht Skipper]

Hi Matt,

Tanks for your reply.
Would the commercial version of delftship make a good bridge between Maxsurf and Michelet. That may be the easier way, through IGES export.

Has anybody tried it ?

I'm planing to get the delftship pro anyway as I like they're linedrawing export and hydrostatic report a lot.

Which software would you use the daggerboard ?

Mat

[Guest625101138]

Originally Posted by Yacht Skipper

Hello,

I'm investigating the resistance of a few hulls options for a 90 feet Sailing Cats.

1. Does Michelet analyse the underbody with the appendages ?
Does it take in consideration the foiled dagger board lift and drag ?

2. I designed the hulls in Maxsurf, how do I export to Michelet ?

Thanks in advance

Mat

You are really doing this back to front. It is better to start with Michlet/Godzilla to give the basic underwater shape of the optimum hull.

With a cat you have to decide on what hull loading condition is most important. In extreme case to windward one hull takes the entire displacement so this means you might be interested in its performance as a monohull rather than a cat - the windward hull simply being flying ballast. Direct downwind you have displacement equally shared as would be the case when motoring although the trim would be different in the two cases.

I expect with a 90ft cat you would not be pressing much above hull speed unless you are going for world records. (It is interesting that a smaller cat is actually faster for a given sail area ratio in the normal speeds of interest but there are other reasons than speed for going bigger.)

Once you know what the optimum hull looks like for the various points of sailing you can then see how your variations compare with it. For example you can find the extra power required to make a wider hull.

Delftship pro will import igs files so this is a good path to get a Michlet file.

Delftship has a keel and rudder wizard so it is easy to generate certain common profiles. As long as these are included in the hydrostatics they will be exported.

Rick W