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.

Step 2: Major Marks and Cuts

Roll out your cloth.
Cut it a few inches longer than your boat.
Fold it in half.
Mark the center line with pencil. This line will follow the keel.
Lay the cloth on your hull with the pencil line down the center of the keel.
Stretch the cloth tight end to end the length of the keel. Clamp it in place at the stem knuckles (where the keel meets the stems) with whatever kind of clamps you have.
Pull the ends of cloth to fit around the bow and mark where to sew it together with pencil.

Step 3: Break Sewing Machine

To get warmed up I fired up the machine and sewed up some rips in my board shorts. I was thinking my machine was pretty good. Then it made bad sounds and plastic gear teeth fell out of it.

Damn.

I've got one thing to say to you. Plastics. SUCK!!!!
For gears anyway. If I were going to invent a field and call it "engineering", I'd teach my students that if you make a nub out of a material ten times weaker, you should make it ten times bigger.
Unfortunately, when they put plastic gears in these machines, they made them the same size as the metal ones. They were 100 times weaker than the metal ones when they were new, but then the plastic started it's molecular oozing process and turned to cheese. We're all fond of saying that plastic never decays. But it does turn into useless oog.

Why oh why did the Singer Nibelungs make their gears out of plastic cheese?
I carried this sewing machine all the way here and it spits teeth after ten minutes?

Step 4: Find Sucky Replacement Gear and Give Up

After some tantrums and a nap, I get on the phone to Roy at "Sew Special", who was raised by sewing machines. He's the "cider house rules" type boy doctor of them.

Of course he has the gear I need. He gently chides me for owning a "touch and swear" machine.
He: "I thought they'd all been. Something."

A trip to town and I have a new gear. Brand new. Brand name brand new. It's never been out of it's little plastic bag since it was made 17.5 years ago. Unfortunately when I get back I poke it with my fingernail. That's a test for hardness taught in science class in U.S. schools. I determine that my new gear is very much softer than a fingernail. They should have made the gears out of fingernails.

I don't try to return it to Roy. I'm too afraid he'll say something wise and gentle to me while giving me my $9 back.

I check craigslist. No deals. All 70,000 of the nice ladies on the island are trying to get one to sew Hawaiian quilts and kine(stuff like that) cozyoids(I made it up) for her Ohana (extended family).

I can't buy a NEW one, because they're..

horrible.

You've seen them. Plastic knobulated pfaffenkugels. They are the microeconomic equivalent of fishing lures. The salesman drags them past the fish and the fish bites the one with the most jingles on it.
New machines can sew ornamental buttonholes in a demo room which is what the customer wants at buying time. Unfortunately they can't sew denim at home, which is the customer needs for the rest of their life.
"Microeconomics" is the study of why individuals spend money.
It's the same as "Psychology", but there's no Nobel prize for psychology, so it got a new name.
Actually there's no Nobel Prize for economics either, but there is a prize "in memory of Alfred Nobel" (w'pedia) funded by the Swedish state bank.
The peace prize is mostly given to mass murderers to encourage them to be better, and to prominent vulnerable activists to delay their assassinations. I don't know what the Econ prize is used for.

I've run out of time and have to go back to the mainland.
I lost at least a week of boatbuilding time dealing with tools that kept breaking.

Step 5: Stretch the Skin Over the Keel

The next time I came back to the island I brought a Singer Model 600 with me. It's the same thing as the Model 646 I brought before, but with a "triple stitch" feature. Being 46 digits older, it has metal gears.

Sew across the ends of the skin so it can be hooked over the ends of the canoe.
Pull it very tight so there are no wrinkles at the keel.

Step 6: Fit the Skin Over the Stems

The two ends of your canoe are probably aren't the same, so make sure the cloth doesn't get turned around after its fitted. Put some dirty footprints on one end of the cloth so you can recognize which end is which.

Pull the cloth as tight as you can over your hull and clamp it in place. If your hull shape has a lot of compounding (Marilyn Monroe) you might need to sew some darts like a fitted dress.

Mark both sides of the cloth along the stem as seen here. When you sew this seam, use the average of both lines. Put it back on the boat to check it. If it's too loose, sew another line of stitching closer in to pull it tighter. Repeat until it's as tight as you can stand to make it.

Step 7: Bobbin Loading on Touch&Sew Machines

I've now brought two "Touch&Sew" machines to the island. A model 646 and now a model 600.
I guess I thought they could share parts or something.
This type of machine is cheap and abundant in mainland thrift stores for good reasons.
This is supposed to be an easy-to-use machine, hence the name.
Actually it's not possible to operate one without a manual. It's much different from a regular machine.

Here's how to load the bobbin.

Find the bobbin autoloading button. It's somewhere on the machine. Usually it's not labeled. This one is over here. It latches down. If you push this button when sewing the machine will choke on thread.
Then you'll need to throw that convenient "throat plate release" lever and cut tumors of thread from down in bobbinsville.

Put the presser foot in the raised position.

Put the bobbin back where it belongs. I know you took it out thinking there was a bobbin loader somewhere on the machine. These bobbins are special. No other bobbin will work on this machine.
Leave the trapdoor over the bobbin open so you can watch what happens next.

The needle is properly threaded. Leave two or three inches of thread hanging out of it.

Now run the machine. The needle will go up and down. The bobbin will spin. Thread will be magically sucked off the needle ans spun onto the bobbin.

Don't get too carried away by the magic. If you overfill the bobbin you'll choke the machine again.
Look through the transparent bobbin and stop before it's half full. There are concentric circles marked on the top of the bobbin.

Release the autoload button.

Lower the foot and sew on something. I usually pull the loop of thread out under the foot and cut it first, but that's just a habit from using conventional machines.

Step 8: Bottom Thread Tension Adjustment on Touch&Sew Sewing Machines

Here's the unlabeled screw that adjusts the bottom thread tension on these Singer model 600 and 646 Touch&Sew sewing machines. If you loosen it too much the little lever that holds the bobbin in place will no longer latch and the machine will choke on thread. If you loosen it even more parts will fall off.

Your unclean desire to loosen the bottom tension so much is due to your lack of top tension.
Make sure the machine is threaded properly.

If you don't know how to thread a machine, open all the doors and look at your machine from all angles. Usually there's a threading diagram hidden on the inside of some door.

Step 9: Mark and Cut the Gunwale Hem

When all the sewing is done we'll turn the skin inside out. I should be marking the other side of the cloth in this photo, because the cloth will be folded up over this line. A line at the outside of the fold would be much easier to see.

Pull off the skin, lay it flat, and mark the hem allowance. I used 3 inches. It's not critical, but keep it the same. I use a block of wood to mark it. Cut at the outer line. I cut both sides at once, making sure I wasn't cutting inside the line on either layer of cloth.

Step 10: "Flat Fell" the Stem Seam

When you're happy with the seam over your stem, fold it over to one side and sew a couple of rows of stitching to hold it flat.
That's called a "flat felled seam". It's very strong, which is why your jeans are mostly sewed that way.

Step 11: Another Sewing Machine Dies

The machine jammed. I couldn't get it to sew. It just kept jamming. I kept having to pull the plate and the bobbin and digging snarls out.

I wasted a lot of time trying to fix it. When it was over I sent this email to Star

The new sewing machine died this am despite the metal gears.
It died in a complex marketing-driven-feature-bloat way.
It has so many features they mechanically divided by zero while sewing and
it ate itself.
I dissected its tiny left-hand-threaded unnecessaries while cursing the
Singer Nibelungs who'd cobbled on so many weird features.
I got the last interlocking piece off and on its underside was the wad of
thread that had played fulcrum to the lethal mantissa.
Before me lay a heap of tiny parts not found in any hardware store.
I put them back onto the machine, and oddly there were none left over. Even
more amazing, the machine sewed just fine after that.
So I finished sewing the skin.

Step 12: Sew Boltrope Into Gunwale Hem

Now that you've made the permanent stem seam, you skin has an inside and an outside. All the messy seams and flaps should end up on the inside of the skin. Make sure you fold the cloth hem along the gunwale toward the inside of the skin.

Cut two lengths of polyester cord a few feet longer than your boat. Fold them into the gunwale hem so they overlap at the sides of the boat and wrap around the bow of the boat.
At the side of the boat, mark the midpoints of the gunwale onto the edge of the cloth.

Sew the gunwale hem. When you get to the side, poke two holes in the hem a foot or so apart.
Pull the ends of the cord out through the holes. The next step shows how.
Between the holes the two cords overlap.

Step 13: Giant Sewing

Poke a hole in the cloth with a marlinspike (this tool used to really be a spike from a marlin), an icepick, a small phillips screwdriver, or a big nail. The best spike will be conical and smooth so it will spread the fibers apart instead of cutting or breaking them.

Make a loop of wire or heavy monofilament. Weed-wacker line would work. Pinch the end so you can poke the loop through the hole in the cloth. Tie the loop to a handle of some kind so you can pull on it without hurting your hand.

Poke the loop through the hole in the cloth.

Put the end of the cord through the loop. Fold it over and try to make it pointy. If the very end of the cord has a jagged blob on it, melt and smooth it.

Use the loop to pull the cord through the cloth.

You'll be doing a lot of this when it comes time to lace the skin onto the hull.

Step 14: Lace the Skin on at the Nose

Drill a row of holes a few inches from the nose.
Clamp the skin in place at the other end of the canoe.
Pull the skin very tight over the keel and stems.
Sew cord through these holes and around the boltrope.
Pull all the lacings as tight as you can without ripping. This is easier if the boltrope is also pulled very tight.

Step 15: Lace the Skin Onto the Frame

Lace the cord back and forth across the deck to pull the skin tight.

Do it like this:

Poke hole under bolt rope in gunwale hem.
Poke loop of wire or monofilament through.
Put cord through loop.
Pull loop out.
Repeat back and forth across the deck.
Pull the cord tight. When you get to the end of a piece of cord, tie on a new one and continue.

If you're poking big holes and pulling small cord, here's another method to try:
melt the cord end and form it into a needle. Poke that through the hole and pull with needlenose pliers.

Step 16: Lace Along Cockpit Rims

When the lacing gets to the cockpits, do it like this.

Mark the lacing points on the skin with pencil.
Use a stick to lay out where the lacing would have gone across the cockpit. Mark the locations on the rim.
Drill holes in the side of the cockpit rim.
Use a backing block to minimize splintering at the exit wound.
Lace the skin to the holes.
Pull it tight.

It ended up being really clean. I hadn't had a good plan to deal with the cockpit lacing, but it just happened this way.

Speaking of clean, this is a good time to vacuum the shavings out of the boat.

Step 17: Ironing Out Wrinkles

The skin is now fully laced. The boat looks amazing. It rings like a drum when you tap it.

There are still a few wrinkles here and there on the boat.
The severe compounding at the forefoot makes the cloth there a little loose.
Polyester shrinks when you iron it.
I carefully iron the loose spots. There is a small improvement.
Make sure not to melt or burn your skin. Or your boat's skin.
Don't ever iron sails. It will distort them and you'll regret it.

Step 18: Beam Sleeves

Remember the sockets for the outrigger crossbeams?
We'll have to cut holes in the skin there. Make sure your lacing straddles these holes, or they will rip out in a horrible way.

Eventually we may sew little sleeves for the beams to fit through the skin.

Step 19: Mask the Dry Part of the Skin

I'm in the tropics and I want the boat to be able to breathe.
I'm going to try leaving the upper part of the skin uncoated.
I mask off the top few inches of the skin.
I use a brush as a spacer and try to make the tape line fair.

Step 20: Varnish the Skin

I painted three coats of varnish onto the lower portion of the cloth hull to waterproof it.
I waited a few hours/overnight between coats. The previous layer is still tacky enough to bond well.

The varnish is "Varathane #93 Clear Satin Spar Urethane" recommended by Wolfgang Brinck. Thanks Wolfgang!
Read the instructions on the can.
Read Wolfgang's instructions.

I knew the fumes were going to be bad. I didn't have a gas mask. Inspired by plans from 1942, I made one from a snorkel, a tin can, and some coconut-husk charcoal. It worked great. No headache.

Mistakes I made, none of them fatal:
Started too late in the day. Dew and insects got on the finish.
Should have vacuumed out all the shavings from inside the boat first. Now some are glued down inside.
Didn't mix the varnish first. Should have read the instructions. When I did I'd already painted a lot of the boat with runny varnish and left the remaining varnish thicker than it should have been.
There was rain and high humidity which slowed the varnish drying. It took almost a week for it to get hard and stop smelling of varnish. I ended up using exactly two quarts. I expected it to take more. If I varnish the rest of the hull, that would take most of a quart.

The varnish shrinks when it dries and makes the skin even tighter. The boat gets better and better, like a fine musical instrument. Which is what it sounds like when you tap it.

How will we keep this nice skin from getting destroyed by rocks? Find out in Chapter 8: Keel and Rub Strips