Tuesday, February 5, 2013

Tech Tip Tuesday

Class has been ticking along with the students getting their frames near completion.  The canoe plans came from S. Jeff Horton's book on skin-on-frame building that's available on Amazon - he's even got a second book available.  

Before you take issue with what I write here and think that I'm throwing Jeff "under the bus" as it were, I'm not.  I think he does some interesting things and offers some good designs, but I think he lacks some experience with other canoe building traditions.  Even he states that he's not really a "canoe guy" and I think that hampers him in designing a skin-on-frame canoe.  I do think that for our application, we've made some improvements to the design in terms of functionality and aesthetics.

He's got what looks to be a great shape for the canoe, but I take issue with a few of his construction details.  First, in his design, he notches the bottom of the frames where a plank boat would have garboards to put in floors.  First, the notching weakens the frames significantly.  While Jeff shows a slightly raised seat in his design, we really want the paddler to sit as low as possible in the canoe. This would have the paddler's butt in any water that might be on the floor if they were sitting that low.  Last but not least, the fabric rides right on the floors, which doesn't allow the fabric to flex over obstacles that you might encounter in the water, resulting in potential damage to the skin. 

To avoid these issues, we didn't notch the frames and will lash a floor to the top of the frames which I think will be a practical and more attractive solution.  It should look very much like "duckboards" used to in a traditional canoe.

The other thing that I've been thinking about for quite some time is how to make the gunwales more traditional in their appearance.  When building a wood and canvas canoe, the ends of the inwale and outwale often have a graceful taper to them and the stem is mortised to allow the gunwale to pass by and give a nice triangular area for the deck to sit within. 

On Jeff's canoe, he has the deck as a "cap deck" which lets him hide the fact that the inwales aren't well fitted.  He claims that this type of woodwork is beyond most, but I think that's a little simplistic.  To be honest, I've been thinking about this for a while and last weekend, we made a test cut on the first boat.

We started by placing the inwale in place and clamping it to the end of the stem.  We made a horizontal mark at the bottom of the inwale.  We also marked the centerline of the stem face.  Using a bevel gage, we took the angle that the inwale met the stem and marked from the centerline to outside faces.  A vertical line completes the marking.

 Using a handsaw, we roughed away the material and finished with a chisel.  Here is the result:

The next step was to take the inwale and taper it from a 1/8" thickness at the end of the stem to full thickness at the first form.  We repeated this for the outwale and made a tapered spacer that went between the inwale and outwale.  The length of the spacer was such that the thickness of the outwale was 7/16" where the spacer ended.  There is an important reason for this - we'll be using 3/8" long staples to attach the fabric to the outwales and don't want the staples poking though into the scupper openings.

I think that the tapered ends look very nice.  We still have a bit to go on this idea yet - Jeff's scupper blocks were irregularly spaced, so we're going to deal with that.  To do that we'll cut down the frames by about half an inch or so in order to hide them with pieces of the Western Red Cedar used for the gunwales allowing us to make more uniformly spaced scuppers.  Also, the stem ends will be cut down and the breasthooks tips will be notched underneath to allow only the deck to be seen, not the end of the stem frame.

More to come!

No comments: