Basla strip solo pack canoe

Hello, i m new on this forum. I m from France, I have build a stripper canoe (freedom 17’, from the canoebuild book).

Freedom 17’
Wood species : fir (buy to the local roofer)
strip : 20mm*6,5mm, bead & cove
Inner and outer stem
inner keel 20mm*20mm
deck in fir
glass fabric and epoxy lamination : 3*80 g/sm outside, 2*80g/sm inside
weight : unfortunately i didn’t weight it (i will do it as soon as i can)

It’s really too heavy, i can’t handle it alone. So i decided to buil a solo pack canoe. I buy the plans from ashes still water boat, and the model is the solo packette. I choose this one because it’s really short, and have a nice thumblehome.

It seem to be really light by design : no deck (just handle), and stemess construction
I want to try to be lighter, so i found this article : just here

He says that he have build a wee lassie in Balsa strip. The density of balsa is 150kg/cubic meter, so it s the lightest wood we can found.
I find 1/4 m³ of balsa on our french craiglist (leboncoin.fr), so i start planking in balsa :


now i’s half planked, and i try to figure out wich lamination i should use :

he use 75 g/sm one layer outside + 1 layer under the waterline, and one layer inside + one layer one the foot area

i m going for
-one layer of 80g/sm outside and inside, + one layer of 50g/sm under the water line
-one yoke, one thwart, two handles, in Ø20mm carbon tube, and for the yoke and the thwart, some triangulation renforcement (see the drawing) in Ø10mm carbon tube.


i m also thinking of use "unidirectionnal carbon ribbon" from easycomposite to add some "ribs like, with this boat design in mind : https://dbt.arch.ethz.ch/skelethon-...novation-26th-concrete-canoe-regatta-germany/

do you have any warnings, or advice to give to me ?
really thank you

 

Gunwhales?

Balsa is going to be pretty weak, so instead of glassing 2x to waterline; go 3" past the main turn (chine) in the boat with the doubling inside and out. Otherwise, your weakest point will be at the turn. The boat doesn't care about the waterline; stresses occur from loading or leaning on sides.

Gunwhales add stiffness to the hull. If you want ultralight gunwhales; you could laminate them from balsa, say 3 strips and just apply them to each side for 3 strips inner and 3 outer on both sides. If you are really going for light; perhaps the carbon tubes? But you need something for the top edges for paddle banging.. EDIT also for seats...credit to @upchurchmr ,the gunwhales also take some beating during loading/hauling. If you want to go ultralight; you can maybe reduce to two lyers of balsa each side of the hull skins.

 

On the outside, laminate the 80 gm cloth diagonally over the entire surface. These diagonals will overlap by 4 to 8 cm. Then laminate 80gm cloth running the length of the hull.
On the inside, laminate 80 gm diagonally gunwale to gunwale in the middle 40% of the boat. Then seal the entire inside with 80 gm cloth. Be careful to seal all tiny holes to prevent water entry.

The hull has large flat areas so 80gm is needed. The diagonal layers increase stiffness in the middle where the greatest load is. Less material is needed in the inside ends of the hull.

 

Yes. To double up on what kayak said, consider neat coat of epoxy at 2 oz/yd to prevent ingress.

 

Hello fellows,
ok i get the idea of diagonal fiber in the 40% middle of the boat. what do you think about using carbon ribbon instead of glass fiber with diagonal layup ?
i draw my idea here :


i think about that because carbon ribbon is very cheap, and i hope it will give equal stiffness than glass fiber, but with more style

 

The need for two layers is also for abrasion from feet or sand/rocks.

 

Yes.
The original dual skin under the water line is for abrasion not stiffness. Changing the core to the far less stiff balsa requires additional stiffening FG.

Weight savings by choosing a lighter core may be more than absorbed by the thicker FG requirements.

 

The other obvious problem with the ribboning outside is that would create an uneven exterior which would add to drag.

 

A single ribbon of CF does not add enough stiffness to form a "rib". You need some thickness for a rib. So multiple plys of CF should be used. How much? No idea.
Normally there would be something to raise the CF off the skin surface.
Not a good idea on the outside due to drag.

Time to make a test of various geometries and then bust them.
Ultralight always is an experimental process, unless someone has made a successful boat you can copy.
Expect to need to make more than one boat to get everything successful.
Any single feature can cause a failure point.

You need gunwales as said above, otherwise the boat will break at the top of the sides, about where you seat yourself. Probably as soon as your weight gets in the boat.

Good luck and please keep telling us about your progress, good or bad. Others can benefit from this experiment.

Note that there were balsa/glass/ epoxy canoes made in Australia or New Zealand - as I remember - but I can't give you a reference. But they were successful but delicate.
Perhaps you could find something at AYRS.

Remember that CF is not magic. You need enough to produce the required strength.

 

maybe you talk about this article from M. Storer, and yes it's the start of my reflection.

Ok. i try to sum up your remarks in this drawing :
a cross section at the beam

 

It is going to be very light as drawn by Storer; do not attempt to make it lighter or it'll end up weak and break. The inside with a single layer of glass is rather light and will wear quickly. Either a neat coat or two of epoxy should be added, or a second layer of fabric up a few inches above the chine. Neat coats are applied at 2 oz/yard. So, a four oz glass is 8 oz with resin at 100% and two neat coats are half of that and they fill the weave and prevent boot wear on the tops of the glass strands, etc. However, I prefer the roughness of the glass inside, so I'd add the glass and then it must be varnished for uv or it will chalk off.

 

Hello,
I have just finished the planking. I weighed the balsa hull after carefully removing it from the mold : 3.34 kg / 7 lbs 5 oz
I took the opportunity to weigh the strongback and the mold too (112lbs), so I will be able to precisely weigh the weight of the glass, the epoxy, interior / exterior. I will report all of this to you.
Now i have to wait for the delivery of the epoxy bucket.

My feeling with the "wood only" hull in the hands : the chine is very curved, it gives a lot of strength. On the other hand, the almost flat bottom is completely soft. The carbon ribbon and the extra thickness on the inner keel line are definitely needed. (as drawn above)

 

No hull bottom deserves a malign treatment of ridges of laminate. Don't do it. The hull will drag.

 

The wood is a core, it could just as well be foam, strength is not required. The carbon strapping does nothing to improve that, strength comes from the fiberglass skin. If your skin were carbon, the straps would improve diagonal strength, but since they will be glass they do nothing since the properties don't match.
Just glass the thing, if it's still to flimsy add another layer of glass.