Building an Outrigger Canoe

[spenny]

Aloha all

I'm working on a personal project to build a 6-man outrigger canoe for racing. To build the boat I'm looking at wood construction instead of composite materials for ease on the wallet.

I've strip planked 3 one mane outrigger canoes in the past, 2 were of divinicel foam and backed with 6 oz S glass, while the third was yellow cedar with 6oz S-glass again. I'm looking at doing this canoe as a cold mold instead of strips hoping to make it stronger and lighter.

My main question that I'm hoping people can shed some light onto is;

1) Is it possible to build the canoe as a solid "tube". I imagine having the station molds "strung" together with a piece of 2" square metal pipe leaving the nose and the tail to be built separate and added after construction.

a) Constructing it in this manner would eliminate gluing the deck and hull together, but would be almost impossible to glass the interior of the canoe. Only the areas close to where the paddlers will sit will have glass to protect the wood from higher wear (because that's as far as I can reach inside the decked boat with just the cockpits cut out).

Materials for the project will be 3 layers of 3mm okoume and sapelle plywood. Calculated weight for the finished canoe is around 200lbs. The lighter the better, but strength is obviously important. We paddle in some pretty extreme conditions and I can't have a boat falling apart on me between Molokai and Oahu in 25ft + seas!

Curious peoples thoughts on if the solid boat can be built or if I have to do deck and hull separate.

Thank you

[ancient kayaker]

I'm not familiar with this class of canoe but my thoughts are:

I assume the metal tube is just for a construction strongback and will be removed before closing the hull, as it will not contribute much apart from weight to the finished hull. Are there to be any provisions for supplies and also inspection of closed volumes? If you don't want to glass the inside then there is no reason to have the deck as a separate removable assembly and it can be built right on the boat - for this kind of service it would seem inadvisable to construct it without bulkheads.

[philSweet]

Usually, one can't choose the hullform, build materials, and build method separately. They should be treated as one problem and evolve in your mind together. If it is going to be a cold molded boat, then use those methods. If you want to explore different methods you will probably not be cold molding it. Please post detailed drawings of your proposed build and pictures of the current state of the art. When entering into a new class of racing, it is usually best to blatantly copy the current champs as a first attempt. Especially when the class has a history stretching back some thousands of years.

If it is going to be cold molded, the joint does not have to be a "shoebox" deck on hull joint. You can go for halfhulls joined on the centerline if you prefer. This can be handy for the outrigger if it is symmetrical.

[variverrunner]

Spenny. A simple sketch of your idea would probably help everyone to understnd your concept

Allan

[spenny]

yea, I'll spend some time today on sketching up my concept.

It would be very similar to how a normal cold mold is done; station molds, ribands, and the tube running the center to give support for the molds then braced on either ends so the wrapping of the plys will be continuous - like a barber pole.

Here is a drawing of a canoe that a friend is working on, he designed it and will build it with his team in Tahiti. He will be stripping his version with 1/2" thick 2"wide strips.

Mine will be similar, but I'm pretty set on the cold mold.

[TeddyDiver]

Originally Posted by spenny

Materials for the project will be 3 layers of 3mm okoume and sapelle plywood. Calculated weight for the finished canoe is around 200lbs. The lighter the better, but strength is obviously important. We paddle in some pretty extreme conditions and I can't have a boat falling apart on me between Molokai and Oahu in 25ft + seas!

Have you made any calcs about the strength? At first sight it feels a bit thick. What's the orientation the layers?.
Just my opinion but maybe smth like 2mm transverse and 3mm longitudinal veneers could do the job. Doing it tube make bulkheads/ribs and longitudinal strips which work as the jig/mold to be left in place and works as a part of the construction. This will support the stucture more and you can use a bit heavier glassing outside with less weight than the 4mm more of ply..
Having a tube as a strongback throw the structure is a great idea. You can roll the hull during the work to best position freely when you support it only from the ends. But you need quite a tube..
Once more, just my 2c
BR Teddy

[spenny]

I haven't done any test panels yet for strength, just basic weight calculations.

I'm glad you picked up on the concept of me trying to roll the whole mold to construct it. I haven't seen if it's ever been done before hence this thread.

So you think it might be too thick with 6mm total? I looked at doing 3 layers of 1.5mm even with the extra epoxy between layers would come out significantly lighter than the 6mm. Angles would be 90 degrees for the first two then fore to aft for the final layer.

Looking at some threads where people discuss the merits of Xynole cloth instead of fibreglass - however it appears that xynole doesn't wet out clear, I want the wood shown through on the hull (if I work with wood I like to showcase it).

Keep it all coming - makes me think - ow ow ow I smell burning!

[TeddyDiver]

Originally Posted by spenny

So you think it might be too thick with 6mm total? I looked at doing 3 layers of 1.5mm even with the extra epoxy between layers would come out significantly lighter than the 6mm. Angles would be 90 degrees for the first two then fore to aft for the final layer.

Sorry.. there's in your opening post "3 layers of 3mm okoume and sapelle plywood" so understood it's 9mm together, but 4.5 to 6 sounds better. Note "sounds" bcs there's no math behind. D Gerr's scantlings give for strip planked hull thickness from 7 to 8.5mm depending of the sheathing alternatives, but that's on the safe side for sure. Anyway believe with this Length Beam ratio the bending forces of the hull are the most important factor.. Maybe some NA:s will give some insight..