: I am planning on building a SOF Wee Lassie knock off and have my first
: question about construction. I'm planning on using cross sections (aka
: Yost boats) that are modeled off the strip forms from the Featherweight
: Boatbuilding book. I've done this before and I know its possible. I will
: have one or two forms in the sitting area that will be open ended. There
: will be two more forms that will have tops to them and plan on adding
: breast hooks into the tips.
: So my question...
: Right know I'm curious about what gives canoe gunwalls their strength.

Check out www.gaboats.com. This is the site for geodesic Airolite designs--probably the lightest skin on frame boats around. You'll get a few ideas about construction of your SOF canoe.

: If I
: use a 3/4 inch (by 1.5 inch) gunwalls with breast hooks and two
: forms/thwarts (.5 inch plywood), will the gunwalls hold their shape and
: not crush the open ended forms where the gunwalls are at thier widest? I
: also do not plan on making inwalls or outwalls. Will this work? What gives
: the gunwalls strength in a canoe anyway?

First, the term is "wale", not "wall", and the pronunciation of "gunwales" is usually "gunnells".

Whatever we call it, it is the thick, upper edge of the side of the canoe. Its strength comes from the material it is made of, and varies with the size of that material. A gunwale made from an oak 2x4 is going to be stronger than one made from a 1/4 by 3/4 inch cedar strip --and much bigger than one would need for a canoe.

Bending an oak 2x4, or any thick piece of wood, is a chore. You can do it by steaming the wood, or you can make the gunwale from 2 or more thinner strips which are laminated. If you use two strips of wood and place them both inside the hull material then they are inwales. I fthey are on the outside, then you have a two part outwale. If you put half on the outside and the other half on the inside, then you have inwales and outwales. The latter method is very common. The outer wale gets a lot of abuse. Sometimes it is called a rub strip. If it is attached with screws it can be removed after a few years and a new one screwed in place.

The gunwales and the keel Or keelson) are the main structural elements on a canoe. The ribs connect the keel with the gunwales sio that stresses can be distributed and shared along them. Water pressure on the outside of the boat acts to squeeze the boat together. Thwarts running across the boat, from one gunwale to the other, resist this squeeze. The more weight you put in a canoe the more water it displaces. The greater the displacement, the greater the pressure on the thwarts and gunwales. You want to design thwarts which will allow the boat to be completely submerged without collapsing. That would be a "worst case scenario". Plain 1/2 inch plywood is not going to do the job.
However, if you are making a couple of building forms from 1/2 inch plywood, and you glue and screw(or nail) a 1-1/2 inch wide strip of plywood to the the top edge of that form (so that the cross section looks like a "T") you could make a very strong thwart very easily.

The longer the boat, the more thwarts you need. with an 8 tr 12 foot boat (typical for a Wee Lassie) you can usually get away with a single thwart. This doesn't need to be in the middle of the boat. Many people put it just behind the paddler and use it as a back rest.

: I ask this because I've made a couple kayaks, but they are loaded with deck
: beams to keep the gunwalls strong. I have no experience with canoes. I'm
: amazed by canoe's gunwalls strength concicering they only have breast
: hooks and one thwart giving them shape.

Breasthooks are mostly decorative. For function all you need is a good connection between the end of the keel and the ends of the gunwales. A breasthook is just a block of wood that you cna drive screws into to hold the ends of these parts. Birch bark canoes just used lashings.

Speaking of birchbark canoes. When these are made the outer wales are made first and staked out on the ground in the desired "football" shape, which maybe obtained by using some light thwarts. This frame is raised off the ground and supported by sticks. The birchbark is rolled over this shape, and pushed through it to give the rough shape of the canoe. The ends are stitched up, Ribs are forced into place, then the inwales are attached. By running a lashing around inwale and outwale, with the cord going through a hole in the bark, the gunwale is pulled together and pinches the ribs and bark in place. The keel is inserted and lashed to the ribs along the center line of the boat, and after holes are patched the thing is launched.

When big birch trees became hrd to find, builders added thin planks of wood (usually cedar) outside the ribs, and covered the boat with thick canvas, which was waterproofed with several coats of paint.

For a boat 8 to 12 feet long I'd use a gunwale that was 3/4" to 1-1/4 inches thick, and make it in two pieces which would each be about 1/2 inch thick. Maybe 1/2 inch for the outside one and 3/8 on the inside. That would give me something to grip when I went to pick up the canoe.

Hope this helps

PGJ