Sailing Canoe Chapter 7: Sew a Skin over the Hull Skeleton and Seal it.

There are a lot of tricks to this process, a few new tools, and a few broken ones. The skin of this canoe is very important structurally. All the tension is carried by the skin and all the compression by the frame. It turned out really well.
I sewed the skin from "Luff Cloth" which is heavy uncoated polyester canvas given me by a sailmaker pal. I laced it tight with 5/32" polypropylene cord.
I painted it with "Varathane #93 Clear Satin Spar Urethane" recommended by Wolfgang Brinck. His kayak skin instructions are really good.

Continues from
Chapter 1: Make the Deck, Keel, and Cockpits
Chapter 2: Make Ribs
Chapter 3: Lash the Frame
Chapter 4: Carve outrigger and Break tools
Chapter 5: Hull Frame Finishing
Chapter 6: Morton's Oar

Followed by:
Chapter 8: Keel and Rub Strips
Chapter 9: Dipaakak
Chapter 10: Independent Suspension
Chapter X: Maiden Voyage

Please support the WAM canoe project as they preserve and foster canoe knowledge in the Marshall Islands.

Step 1 Test Your Cloth and Coatings

You need to test your cloth to see how it reacts to water. Cotton gets tighter when wet. Nylon gets a lot looser.

You need to test your coating to make sure it will stick to your cloth and not be wrecked by water.
If your cloth gets loose when wet, your coating needs to fully encapsulate the cloth fibers.

A bad cloth/coating combination can wreck a boat skin.
A wrinkly skin is slow and makes a bendy weak boat.
Nylon requires particular attention. It elongates ~10% when it gets wet. That's why your tent is so saggy in the rain and so tight when the sun comes out. If you use nylon for a boat skin your coating has to fully encapsulate the fibers and keep moisture off them. Most random coatings don't do that.

I think my cloth is polyester and I think it won't elongate when wet. I test it anyway.
I cut a strip of cloth a yard long. I wet it and measure it again. It's okay. I paint a dry piece of cloth with the varnish I intend to seal it with. I put it under a lamp to dry because I'm in a hurry. The coating seems to soak in and bond fine. It's not brittle, but that usually develops later. Wolfgang tells me it's good stuff. He's tried and seen almost everything.

Some combinations that I've seen:

THIS IS A TABLE - I WISH IBLES LET ME USE SPACE ' ' CHARACTERS

Cloth Coating
Cotton Anything- It works great and needs to be replaced in 5 years.
Cotton Rubber latex roof paint (Cozy Boat, Wolfgang)
Cotton Catalyzed Polyester resin mixed with Rustoleum (Boston Currach Club)
Cotton Thompson's WaterSeal, then Oilbased paint. (Wolfgang's book "Aleutian Kayak")
Nylon Neoprene thinned very much, followed by Hypalon (George Dyson's book "Baidarka")
Nylon Not Acrylic Artist medium is a disaster (me)
Nylon Not Just Anything. Most things don't stick or don't seal.
Nylon Varathane #93 Clear Satin Spar Urethane (Wolfgang, Follow his directions)
Polyester Varathane #93 Clear Satin Spar Urethane (Wolfgang, this boat)
Polyester Anything is survivable. Even if it flakes off the skin will stay tight and you can re-coat.
Any_cloth Not Epoxy. Most epoxies are too rigid and the skin will crack. The coating needs to be more elastic than the cloth fibers.
Any_cloth Not Polyester resin. It's also too brittle, and It doesn't adhere or encapsulate as well as epoxy.

Exceptions to the last two rules are where the cloth is fully supported by planks or foam. Then you can use hard resins to "fiberglass" it on there. In the good old days they called fiberglass FRP(fiber reinforced plastic) because they used all kinds of cloth, not just fiberglass cloth.

Comments

[HappyHeadCase]

I love your description of battling with sewing machine "engineering". I've had to teach myself basic mechanics on the fly while trouble-shooting the problems with my own (NEW) Singer machine, and have come to the conclusion that I could probably design and build a better machine with no prior knowledge. As you say, the extra features divide by zero. In the end, all we really want is a machine that can straight-stitch and zig-zag. I'm really enjoying this build, as well as your commentary.

[reeeky2001]

I'm amazed! I have a T&S 2 and I've not been able to find out how to load my bobbin. I'm hoping when I get home tomorrow that I'll be able to find this hidden button on mine.

[drbill]

Go talk to the guy at the regester at the sally in Lahina. I'm sure they have sewing machines today.

[Wade Tarzia]

Great -- its going to be like a synthetic sea mammal!

[carpespasm]

Day-glo sea lions?

[omnibot]

Wow, your canoe is really coming along well. I'm following your progress with great interest.

[gmoon]

Like yer paintin' snorkel, Tim. I have an old Klepper (Super 6) folding kayak; the skin needs replacing. Lot of good info here. Hope to make use of it...thanks.