Big Canoe Trimaran.

I want to make a Trimaran out of a big old Grumman 20-foot canoe and the remains of a Paper Tiger utility 14-Foot Catamaran. I am not crazy but I have both of these boats and looks like it would work to me just sitting here eyeing the parts. I got the catamaran because I had an interest in learning to sail and it was being sold cheep. It came with an extra mast and sails off of a slightly larger sailboat and a gallon can full of “ragging parts”. The catamaran is just too small for me as Big Canoe refers to me more than the boat I have, I am not the right body shape to be sitting on a trampoline or hanging my but in a mesh net between the cross braces. I need a seat to put my wide load in. I guess my first question is will the eight-foot width of the cat be sufficient when the 2 boats are U-Bolted together or should I get longer cross braces, maybe ten or twelve feet? The second question is what should I use if I do need longer cross braces? The ones on the catamaran are mast extrusion but that is kind of expensive stuff if purchased new. Is their a stock material that would work?
Big Canoe

 

The ones on the catamaran are mast extrusion but that is kind of expensive stuff if purchased new. Is their a stock material that would work?

The folks that sell lumber for rigging exterior scaffolding are the cheapest source for clear lightweight Spruce.

FAST FRED

 

Hi Big Canoe! I think that your project should work fine except that the existing crossbeams at 7' long are too short and need replacing.
Aluminium tubing is probably the most practical solution and not too expensive. If you are going to use the rig slightly larger than that off a Paper Tiger and sit in the centre hull then you should be going for an overall beam of around 12 feet.
I would think that around 3" diameter tube should be OK, not too thin walled as thin walls crumple fairly easily under high load. Are you going to sail one up or with a passenger? This will matter for strength purposes of your connecting structure. Have a look at a very nice tri about the same size at
http://www.boatsports.com.au/magnum.html

 

Passenger

Passenger is a possibility sometimes, family visits and such. I intend to stay in the center hull as much as possible.
Big Canoe

 

Structure

Is this a Grumman, as in hydro-formed and riveted aluminum hull, Grumman?

It's likely you're going to need to do some beefing-up of the hull structure, especially around the forward beam, to be able to handle the generated loads from the cat's rig. A bulkhead at each of the beams should be sufficient if you can anchor them properly to the aluminum hull and tie that structure to the beams.

You'll probably find that 100 sq. ft. of sail will require that you deck, at least, the hull forward of the beam and find a suitable method for deflecting waves along the midships compartment. I sail a lot of trimaran/canoe designs and these are the areas where you will be taking the most water.

You'll find that a 100 ft. sail will drive this type of boat in a lively fashion and it should be a lot of fun.

 

aluminum Grumman.

Yes it is a aluminum Grumman. It is one of the hard to find 20-foot guide canoes they made years ago. 1100 pounds maximum load so I am very surprised to hear I will need to reinforce any thing. I am glad I learned about it before folding the hull. I can build some bulkheads from aluminum and rivet them in to the framework. I know better than to pierce the hull even for a bulkhead.
It is very gratifying to hear it will be reasonably fast. I am not looking to win any races here but going fast enough to feel exciting would be nice. Decking over some of the top will be easy also. I can just take some thin aluminum sheets and bow them slightly over a light frame. Should be strong and removable if I want to use it as a canoe again. I am mot sure how big the sails I have are. The old guy I got them from was not very informative. I will be joining the local sailing club as soon as I have the framework together and the mast set. I know I will need help to rig the thing and learn how to sail it.
Big Canoe