Canoe Catamaran

[BlackSnow]

My friend and I built a canoe catamaran last spring. We used two Nice Canoes from bateau.com, which we had built a few years back. A flagpole was used for the mast and a white polytarp for the sail.

I used a 1/2" piece of plywood for a leeboard. Unfortunately, the mounting was not satisfactory and it broke under use. We tried to make some repairs using "local" materials. My advice: use a very large/strong bearing on the leeboard.

It was fun to sail but would not point worth a damn. Possibly with a better leeboard design/placement it would have worked somewhat better.

We were able to carry a ton of camping gear. Attached are some pics of us on the Turtle Flambeau Flowage in northern Wisconsin.

There is a book on canoe sail design that I found very helpful. I can't find the title right now, but will try to post later.

Let me know if I can help out with your project. I am a mechanical engineer as well.

Cheers!

Greg

[Petros]

what a great set up! Keep it simple and have fun with it.

I ran across a simplifying design assumption that has worked pretty well for small boats. Assume that at max condition you will get about 1 pound per square foot of sail area of lateral force. With this you can design the mast and rigging, and the loads on the lee or dagger board. It have found it conservative for recreational sail boats and yet does not over design it. It is also simple to work up the forces on the rigging and hull using this design rule of thumb. You do not have to do a lot of calculations to determine the rigging loads.

If you intend to use it in higher winds (about 15 knots) you might add a 1.5 safety factor on top of this.

If you better understood the forces on the lee board you would have known it was not attached to the hulls good enough for the forces you were generating.

[kmeastman]

I have done some drag calculations and it is within acceptable limits, which is good because I never intended to change the canoe hull very much. I know there are probably better hull shapes but I am most interested in the cargo capacity of the canoes so that is a compromise I'm willing to make.

to Rwatson, The technique for finding the center off lateral resistance that you mention is in one of the books I have been looking at. Don't know if anyone uses it, I didn't. After modeling the canoe in SolidWorks, I was able to cut a section down the middle and make solidworks create the projected area and centroid of that area. The Center of Buoyancy, LWL, and volume displaced at various levels in the water were found similarly.

I am still having difficulty determining if a centerboard is necessary or not. I assume there is some reccomendation based on the lateral projected area vs. sail size but I have yet to find one. How do I know if I need one and if so, how big do I make it.

Thanks for your help
Kevin

[kmeastman]

Greg,

I am very interested in your design. It seems very similar to mine. Here are a few of the differences though, tell me what you think of them.

I was intending to buy aluminum canoes, It looks like you made your own out of plywood and fiberglass. Any idea what the weight of the canoe by itself is? Any idea of the weight capacity of the total boat is?

I was kind of worried about using a fiberglass canoe because it might flex and crack near where the brackets are attached, is that really a problem? Also, it was difficult to tell from your pictures how the bracing was attached to the canoes. The reason I ask is that I also intend to make the bracing in a way that can be quickly disconnected to portage between lakes if needed. I was thinking of A permanant bracket on the canoes that would be a hollow tube that the bracing would slide into and then line up two holes and pin it with a trailer hitch pin.


I also intended mine to be much wider, possibly up to 6' between canoes for a hammock area between to put people or cargo.

My sail area to displacement ratio will probably be pretty low when fully loaded. Was yours also low, did it sail well in low/moderate wind and did it make that much difference whether it was loaded up or not?

Thanks for your help
Kevin

How did you go about sizing the leeboard, and what do you think made the boat so unsteerable?