Whaleback Proa
Paul:
I’ve been following your build for a little while now. There is no quality that I admire more than “Git ‘er done”.
Sometimes you might want to consider the option of backing up and re-working things that may be easily improved. Your tacking design will be loading the “beams” in both compression and extension (changing each tack as your “Atlantic” proa become a “Pacific”. The loads your boat will generate are not trivial, especially since you have a 90 degree corner in the middle of the effective beam structure.
I’m sure you are aware of this, as your reinforcements and mods look to address this by adding more structure.
Quite often in boat building, less is more. One and one half sheets of 1/4 inch plywood, scarfed together to make a 12 foot length and ripped into 4 inch strips could easily be laminated and curved to form solid curved beams that could do the job with much more overall strength and much lower weight. Not that pretty matters to beam strength calculation, but it would also be a lot more pretty. If you did this you could get rid of the risers, and the weak 2x4 planks, making your boat simpler, lighter and stronger.
If you count the possible repair time that may be needed if you continue with the current riser design, re-working the beams would probably get you on the water faster and more often. I’d also consider inserting a plywood bulkhead box structure inside the “outrigger” that the “beam” connects to. Even the 1/4 plywood can form effective and strong bulkheads inside your outriggers.
Making a peanut butter consistency goo with epoxy and colloidal silica (fine sandy stuff with fibres) works really well to help gluing down things. This is far better than just painting on epoxy and then putting fibreglass on top. Using your finger or a rounded spoon the make the goo fill the corners in a rounded way is called filleting.
It is surprising, but adding a curve to a beam makes it stronger. Also, having two strong skins over a lightweight filling (or core) is stronger and much lighter than a solid surface of just the two strong skins laminated together without the core.
From all your videos, there is a lot of evidence you are getting pretty good at this boat building stuff. I’m willing to bet with a little bit of help you could make your Whaleback proa stronger, lighter, faster and safer - in less time than it takes to build it the hard way.
Feel free to ignore this and proceed. The most memorable lessons we learn, we learn by ourselves.
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Bill in Ottawa
What are some options for a curved outrigger crossbeam?
Laminated plywood, solid beam
Laminated softwood, solid beam
Plywood box, stitch and glue, covered with glass/epoxy, hollow beam
Other options?
What are some options for a curved outrigger crossbeam?
Laminated plywood, solid beam
Laminated softwood, solid beam
Plywood box, stitch and glue, covered with glass/epoxy, hollow beam
Other options?
Cedar stripped - this is what is done on CLC’s Madness. I’ve seen stripped beams on Tremolinos and lots of other boats as well.
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Bill
Do you have any idea of scantlings for a 16 foot outrigger canoe?
When I find out what offset it takes to make my boat sit level, I intend to make bent outrigger booms. I also want to see the forces involved, outriggers are new to me.
I am thinking about a 4” plywood box, stitch and glue, with a 6” top and coved fillets on the outside, with glass tape all around. Tink had a drawing that showed outside coves as a simple way to build a hull.
It is very easy to build light and strong H-beams. Just laminate several pieces of hardwood to the desired shape and cover the top and bottom with flanges of wider plywood. All the fillets are on outside.
Cheers,
Johannes
I wrote the text above in another (wrong) thread earlier today.
Mark wrote this as an answer:
Is it not normally the other way around - ply webs & solid flanges?
Softwood is generally better structurally, though is normally less rot resistant.
H-beams win hands down on ease of construction and can readily be maintained.
That said they are not so good in resisting torsion, which is important. A tube or box section is better.
Mark
I have not tested the “ply webs & solid flanges” but i believe that thicker plywood-flanges ads more torsionel stiffness. Solid wood as flanges can crack if not laminated or covered with several layers of glass and epoxy.
I don’t think lack of torsionell stiffness is a large problem. We want our akas to bend some to lower the stresses on joints connecting the vaka, akas and ama. It is important that they bend only in the right direction.
The stiffness comes from using several akas spaced for and aft.
Cheers,
Johannes
I have seen some pics of Wharram cats that look like they use H-beams.
I have been moving my outrigger hull around and have dropped it a few times. Apparently at some time I dropped it so it fell on the corner of a crate, or something. It punctured a hole in the side of the outrigger hull. This is not a good sign.
Lesson: 1/4” lauan plywood and 4oz glass cloth are not adequate without interior reinforcement with frequent stringers and bulkheads.
This video is as exciting as watching paint dry…
Comment to your video - It is NOT primarily a motor boat, it is a sail boat with a confidence and experience challenge.
Your boat will most likely sail well - and might even be faster under sail than it is under motor power. It certainly will be quieter, smell better and be cheaper to operate.
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Bill S.
I am afraid of it capsizing while I am in the cabin, so at least at first I don’t plan to sail from inside the cabin, only motor. That may change over time.
Paint and glass reinforcing
Lots of little details to take care of. Splash date in a month or two?