Hi TOM

To model a catamaran hull, you need only one surface unless you have a hard chine to model.

All hull design software can use a longitudinal symmetry plan so you only have to model the starboard part of the hull and it will mirror. On a catamaran, you have to option, model the complete hull, move it 1.1meter from the centerline and mirror it (the mirror surface doesn't count like another surface) The other option is to design only one hull (haft of the hull), mirror it to have one slender hull, move it from the center line and copy it. Using the surface copy command will create another surface and you will have to edit both sirface to make the modifications to the hull.

Using a second surface will be useful to model the deck. Even is the deck has a rounded edge with the hull, it is always easier to modem these two separately and blend them together.

While it is possible and difficult to model the rear transom, the default program will close the rear by following the read edge of the hull. It is perfect for a catamaran hull.

The version of Maxsurf that I am familiar with is the 6 surface version. The six surfaces version was useful for modeling watertight compartment in case of a damaged stability analysis where you have to flood certain compartment and look at the stability and the heel of a bigger ship.

THERE IS NO QUESTION IN MY MIND THAT 3 SURFACE PROGRAM IS SUFFICIENT FOR YOUR NEEDS. The only advantage to pick up a six surf. version would be to model keels, bulb keels, bulbous bow and centerboards.

I was using the educational package of Maxsurf and I think that our package was equipped with parametric transformation and with six surfaces. The parametric transformation is the most useful tool to modify a hull. You can tell is: scale the length to 17’ keep, decrease the width to 95% and keep the same height. You should double check if it is not included because scaling is a real time saver for a hull modeling.

As far as hydrostatic, you might be able to get away with upright hydrostatic alone. The intact hydrostatic package would be plenty but you need to know what to make out of the result. Most of the stability packages are meant for commercial craft that have to get a stability certificate. The information that they supply is tailored to the needs of a government agency of a classification society.

BUT THE FIRST COMMENT IS THAT BEFORE PURCHASING ANY SOFTWARE, DOWNLOAD THE DEMO AND TRY IT. This is not a joke, these program are not easy to use and they might not simplify the task that much, the demo programs will allow you to do any thing without saving nor printing. You can work on a hull shape and simply write down the coordinate of control points.

Even at £ 475 , I think that it is a lot of money for a non-commercial use and you should not get discourage by the obscure interface of the program. It is really meant as a CAD program to work using the naval architecture techniques.