Catamaran Design questions

[ChrisC30]

I'm an amateur enthusiast, working on designing my own cruising cat, and I've got afew questions...

Having been considering several construction materials, I'm still trying to work out which might be most cost-effective while also being reasonably sturdy and safe for blue-water extended cruising. What can you tell me about the benefits or disadvantages of...marine plywood with fiberglass over, fiberglass alone, composite?

Using a tape measure and my own home as a rough guide, I've been attempting to plot out exactly how much cabin space I'd need in the hulls to be comfortable. Some friends say 8' wide by 15' long, others say 6' wide and 20' long. I'm expecting to use just enough space for a double-berth, a small sofa, head with shower. What dimensions might be "ideal", without being too big? Trying to keep this cruiser at or under 50' if possible.

I've been trying to work out a retractable daggerboard design for each hull, but obviously the cabin space might get in the way of this. Is there any way the daggerboards might be inward in the cross-section rather than dead center of each hull? How might that effect overall performance? Trying for a reasonably efficient design for offshoring that can also retract some for shallow water or for hauling.

Also, just any design tips or advice would be greatly appreciated. This will be my first multi-hull, if that matters.

[RThompson]

Hi ChrisC30,

I thought I replied last night, obviously not... so,

Designing your own boat is an admirable thing to do.

However, I would be concerned with the problems I don't know about, and even more concerned with the problems I don't know that I don't know about.

You would do well to get hold of a book like "Principles of Yacht Design" by Larrson and Eliasson (spelling?).
Although its not multihull specific, it will give you some insight into the compromises that make a boat, and answer your current questions.

Good luck with your project.

Rob

[p_mazagran]

Good luck, I built my 1.one, 47', ten years ago, now building 2. one 43'. Do not take it for unfriendlyness, but a boat is a very personal choice, so check out designs of production boats, print the specs and layouts, then look into designers, with the time you will get the "feeling" what can be done and how it should be done. You want a "houseboat" or be able to run away from that depression (hurricane)? how much money you want to spend? electronics you can purchase later, but the tons of epoxy and plywood, or even worse, glasfibre, you cannot take away anymore. Take a look at Duflex as an alternative to vacuum infusion, I choose a moderate hard chine design this time as it is much much faster to build and this material asures a light weight hull. But at first you must naswer the frirst questions ;-))) good luck

[brian eiland]

I would suggest that you learn to use the search tool in these forums....very handy.

For instance type in the word 'centerboard' in the search tool and you get side by side centerboards?

Type in center board' and you get some others as well.

Daggerboards, etc, etc

[nero]

Sounds a lot like me ... 2 years ago. If you have the money, buy a plan from some designer. If you don't have the money, buy some study plans. Surf the net, buy one or two books. Visit some expos and go inside the cats. Actually seeing and measuring the inside space of these designs helped me a lot.

Contact the designers who are selling their plans. They are helpful people. Look at a HarryProa. If you decide it is not for you, you will know more of what you want.

Buy and learn a 3D program. NURBS will keep things smooth. I use TouchCAD and VectorWorks on Mac OSX.

Hull length from what I read needs to be about or greater than 14 meters for blue water. Distance between the hull centerlines is important.

Decide on what building technique to use. I chose wood strip planking covered in fiberglass and epoxy. This technique is easy, strong, and inexpensive. And you can build smooth, round shapes with it.

When all this gets done build a scale model of your boat. Make changes and build the second model. This will give you a better idea of what all those wireframe lines on the computer screen really represent.

Figure out what you can finance. The production cats seems to cost between $250,000 and $500,000. They are designed mainly for the tourists. I have bought $16,000 in material for the boat I just started. This should build my 2 hulls, boards, rudders. I guess that $10,000 will buy the materials to finish the build ... including the mast.

Then comes the cost of knotless trampoline mesh, LED's, Plumbing, Wiring, Electronics. ... And the sails. I am keeping my eyes closed on this part at present.

Time and money. As for time, 2 years to get educated and figure out a design. 7 months to build one ... or two hulls? Then another X years to get the rest done. So maybe it is not the material that makes a boat expensive , but all of the time it takes to build one.

Look at all this fun in front of you!

[p_mazagran]

HI Chris:
size matters ;-) old rule of thumb: a mans age in feet boatslength

Hi Nero: ever had an elephant sitting on your foredeck? That is the weight of a bigger wave breaking over the trampoline. I had and it was no pleasure, my trampoline is 1" webbing, each crossing sewn, this time I'll take no mesh, I'll go tennis racket style. Not as comfortable when stepping on, but 80% open, so waterdrain is much better.

My last boat was strip planking too, be carefull to use enough filler or the lumber will be soaked with epoxy and the hull then to heavy. To avoid that and build faster I choose the precut kit from www.schionningdesigns.com.au. I think it is worth its money, you may save later on on everything else as you may upgrade, but what you do wrong on the hull you can never repair and you must be very lucky to sell your boat once a day. I like to build, but I like to sail too!

[nero]

I looked at a couple of Schionning designs. I liked them a lot. Their plan prices are not overly priced as I remember. I think it was their use of balsa cores and the estimated prices to build their boats that I decided to go it alone.

Too much epoxy soaking into the wood? Never heard of this happening on edge grains. Then again better expoxy than water. smile

I have a 3,000 kg margin of error on my design.

[carroll38]

Hi

My Name is Tim Carroll

I have been working on a lightweigh cat that is 38 ft
for sail in our waters

Would like to collaborate.

I am an egineer with composite experince.

I will probably build molds for the design.

Thanks
T Carroll
Carroll38
Carroll38@yahoo.com
239 731 8391

[brian eiland]

Originally Posted by nero

....So maybe it is not the material that makes a boat expensive , but all of the time it takes to build one.

You might have a look at this BoatBuilding Cost Chart I posted on this forum.

And feel free to add new info to it as experience dictates. Its not set in stone.

PS: The original thread subject is here, uncertain of structural matrials in new project