How should I start (hull design for catamaran)

[justinDesign]

I am new to boat design and have a few questions. First let me inform you on my design. I am designing a small fishing vessel that is meant to be used in hazardous conditions like low water and debris laden water. The vessel is meant to be a catamaran and be approximately 12’ by 5’. The vessel is designed for two occupants that will be seated in the individual hulls while underway; this means that the hulls must be at least 20” in depth. This vessel is meant to be powered by an outboard surface drive so there is the possibility of speeds up to 30mph.

Questions:

Hull material:
Due to debris I wish to make the hull of aluminum or stainless but am open to the possibility of using fiberglass or roto-molded providing they can meet my criteria.

Hull design:
I have never designed a hull before and can only assume that making a cat hull is even harder. The good news is that I am very familiar with Rhino and if any advice can be given in this area I can most likely understand. I would really appreciate any tutorials or some 3dm files of cats that I may pull up in Rhino and reference.

Other questions:
How important are chin lines/splash guards (not sure if right terms) on a hull and if I do need them do I have to have them on the inside and outside of the hulls or just the outside edge.

Any recommendations/files/websites are appreciated.

[PAR]

My strong recommendation is forget what you want in a boat and take the Westlawn courses.

Why so rude?. Simply, you want a near bullet proof craft which requires a careful understanding of the principles.

You can guess and die, trying it out in rough conditions, contract to have one designed or learn what you need. The cheapest of the three is learning what you need so contact Dave Geer and friends at West Lawn.

On the other hand, if you want a puddle jumper for casual light air sailing on a well protected lake then "wing it', what's the worst that could happen other then a long swim back to shore?

[alan white]

From your description of the concept, you'd be better off with a monohull planing skiff. There are many reasons for this, but primarily, the monohull has a greater speed potential and less draft. The catamaran would be a better (more efficient) moderate speed performer. I say this based on a 12 ft boat with a 900 lb displacement
Granted, this has been done in a thousand ways already, while powered cats are relatively rare.
It's awfully hard to come up with an original concept for powered water travel. One thing is certain. A monohull has comparatively many times the reserve bouyancy of the catamaran, vital if cargo is involved. With the same length and width, it's also more stable, especially fore and aft.
The cat has less frontal area, which is of advantage when the power is on the low side, say 5-15 hp, and the top speed maybe 15-20 mph.

Alan

[BWD]

So if you are not permanently put off by criticism, welcome and good luck..

I kind of agree with Alan, you can do well with a mono and get in shallower water, have less design and engineering issues, etc. Metal might not be as good for the size you envision. Really thin plate, too flexible, hard to weld etc. SS not the right stuff. I would just do plywood.

If you want books:

"The Nature of Boats" by Gerr is a good intro to the issues and vocabulary.

"The Gougeon Brothers on Boat Construction" is the bible for wood/epoxy building. It is good for vocabulary, technical info and readability, plus practical advice. Great because it gives an overview of the process of several types of construction, from plans to finish, even if you choose not to use wood, you can learn a lot from this book.

"Principles of Yacht Design" by Larsson if you hunger for a textbook and some quantitative stuff.

And there's always http://www.usna.edu/naoe/courses/en200.htm for a legitimate, if specialized start at the real engineering side of things. Or you could go to boat skool, do westlawn etc.

Your original idea poses some challenges. Would be cool to see how it evolves. best luck.