Questions about Small Cruising Catamaran Design and Construction

Your boat will sail if you get a few things right.

Each hull has to have enough flotation for the total weight and you need extra freeboard. This can be particularly important at the bow.

The sail center of area and the centerboard center of area has to be well matched or the boat will not track and turn well.

The rudders have to be big enough to control the boat.

It all has to be strong enough.

Marine ply is not necessary, but trying to pick exterior ply with as few voids/ repairs is what makes the ply strong enough. Be sure to get ply with 3 equal thickness plies as a minimum. Avoid anything that has thin face plies.

What are you thinking of for the sail/ rig?
Catamarans can develop a lot of power, so the mast/ stays needs to be big enough.

Chines can work just fine. Most cats of this size (even up to 20') only have stations at each cross beam. And those usually have large interior holes instead of being solid.

Have fun.

 

Have a look at the last few pages of my thread "modern hirondelle". Manfred posted some interesting pictures of small cruising catamarans, and we link to some other things you might find interesting.

Ply comes in sheets of 8' x 4' generally. 12' is one and a half sheets. So you're not the problem of joining them but your not using the full double length. Regardless of whether you got chined or tortured your making work for yourself.

Personally I take the path of least resistence. 16' 2 full sheets long, tortured ply less work. Adequate displacement long waterline less hobbyhorsing. If you do something like a capercat with lockers in teh hulls it'll be a nice little coastal cruiser.

Also look at the nacra 350. That's a 12' cat they use a lot of freeboard to allow it to carry 2 crew in a tiny boat. My V3.5 cat is almost awash with just me aboard, your going to struggle to carry gear and supplies on a low freeboard 12' cat.

http://www.briscatamaran.com.au/fun/nacra-350

 

So, it's a personal project....Getting for free or low cost the materials for a personal project needs an outstanding presentation. That will take time a lots of efforts.
Do not forget that the second and most expensive part is the rigging, sails and hardware. Make a detailed excel sheet, and take a deep breath before reading the results...

Everything you will draw will float and sail. The only question is how badly.
Everything you will build will float and sail. The only question is how long before dismantling or decaying. Probably it will be as heavy as a dead African male elephant including the tusks.

With sub standards in design and building anything can be done.

Do not forget that such a project is about 3 to 400 hours of building. Alone it's somewhere between five weeks of 70 hours full time, 10 weeks of 40 hours, and very long if you are working hard on your studies. Far more if you include the design and the programming of the CNC for cutting the 6 small pieces of plywood of the bulkheads.

Add the extra time needed to a complete beginner in boat building. Download and have a sharp eye on the Gougeon Brothers book. It's a bible. It's worth its weight in diamonds.

Download and examine in detail the free plans of the very simple but effective 12 feet catamaran in stitch and glue plywood.

Redraw it on your computer, and re calculate it totally: weight, surfaces, volumes, centers, coefficients, projection of center of effort of the sails and the list of materials. Think over the solutions the designer used. That will be your first design exercise...

 

Ahen, if you want spherical curved surfaces you can join bendable and stronger ply and form your hulls by torturing (easy).

 

I'm sorry but I see there some stretches straight or, at least, very far from what I understand as spherical or even cylindrical (it is probably more appropriate to speak of cylindrical). Maybe it's an optical effect and I'm mistaken.

 

Sorry, not so easy with the pics. Hope this is better:

 

I do not think I understand what you mean. I look for something that looks like a spherical surface on that hull and I can not find it.

 

Thank you for your statemant TANSL.

 

I do not understand anything, I'm sorry, but you're welcome, Manfred.pech.