Sunday, April 5, 2009

Details, details...

When we finally get the bottom of the canoe glued together, it is now time to pay attention to the stems. The picture above shows what we normally end up with after stripping. If we had taken pains to finish the stripping very carefully at the bow and stern, we could proceed to fairing and fiberglassing the hull. I like to have my students do one more step and to laminate an outer stem made from hardwood. I think it is a better-looking and more professional detail. I prefer hardwood here because this area - particularly the bow - bears the brunt of any impacts the boat might have. While the fiberglass and epoxy coating on the outside of the canoe is very flexible, and generally will spring back from an impact, the soft cedar of the hull (or stem material) will crush and not come back to it's original shape. This causes a delamination of the fiberglass and epoxy from the wood and generally requires a bit of repair. Hardwood stems tend not to crush as easily and provide for a more durable buffer.

The first thing I like to do is to find out where the end of the inner stems are located along the keel. You can either mark this position before you bond the football in place (note the pencil mark in the picture above - top right...) or you can come out from the line of staple holes at the station nearest the stem and mark a distance of about 1-1/2" towards the end of the canoe. The reason is that you are about to make a cut into the hull to accept the stem and you want to make sure you will be having the inner stem behind your cut. The inner stem hides this cut when you come through the hull, so it will not be seen from the interior. I like to cut down into the hull at an angle as shown above. (The reason is solely cosmetic. You could just cut straight down, but I think you'll like the detail shown in the last picture. ) I then stop cutting when I reach the inner stem. This cut is usually made with a chisel.

Another view - note the lighter colored wood of the stem.

This cut is then extended along the hull up towards the sheer line. I am trying to accomplish three things here. First, I want to have the width be fairly uniform (within about an 1/8" or so) when viewed from the end. I also want it to be a smooth, fair curve when viewed in profile. Last, but not least. I want the "flat" of the rabbet to be perpendicular to the main axis of the canoe so that the stem isn't twisted when it is laminated in place. The canoe shown in these pictures is a Wee Lassie II, designed by Mac McCarthy. I have a small problem with the way the bow and stern are designed, because the profile gives a section that is a bit wide at the bend. This leaves us with a hollow when trying to keep the width constant. This area gets filled with wood flour, epoxy and fumed silica made into a peanut butter consistancy. The stems are then laminated in place after the epoxy cures and is cleaned up. A bevel that matches the cut in the picture above is sanded into the end of a stack of thin strips. A hole is drilled for a small wire nail near the top of the curve to keep the stack of glue-slick strips from sliding. A cleat is installed under the strongback to wrap inner tubes around. With the pack of strips glued up, it is installed and the inner tubes hold the stem together while the glue cures. Note the spring clamp that was used to keep the strips from sliding side to side. Handy.

The picture below shows the end result when you're done fairing and glassing the hull - what you see is a neat little arrow-head detail that I think is pretty sharp-looking. It is particularly impressive when you have contrasting woods for the stem and the hull.

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