mortise cut out

Just a note, this is another process that is more complicated to explain that it is to actually do.

Where the strips have gone from being horizontally adjacent to the inner stems to being vertically on top of them, material needs to be removed for the outer stems to fit flush. In woodworking terms this negative space portion of a joint is called a mortise. This mortise is tapered in cross section in two dimensions. It changes from 3/8″ at the end to the full stem width at the outside. That ugly chop job above is the only picture I got during the process, but it gets a lot cleaner at the end.

It’s a fairly intricate job that you don’t want to rush through. There is essentially just a lot of paring with a narrow chisel. You periodically place your outer stem on to check the fit and score any adjustments onto the strips.

It should be mentioned that the outer stems have been tapered down to 3/8″ at the inboard end. The taper is only on the portion on the bottom of the boat, and only in one dimension to start. the bevelling the other way to match the plank angle is done after the stems are glued into these mortises.

The inboard (narrow) end of the outer stem is also cut about 1″ shorter so that the inner stem overlaps it. If you don’t do this there’s a danger of cutting the mortise back too far and having a hole through the hull with no material behind it.

 

fitting stem

Here’s checking for fit. The mortise taper isn’t quite enough to get the outer stem seated fully to mate with the curve properly.

Once the mortise is just right, the outer stem will fit tight to the inside stem, and be recessed down 1/4″ (or the width of your planking) on the bottom of the boat.

stem fit to mortise

A generous application of epoxy thickened with sanding dust is then put into the mortise and on the outside surface of your inside stems. The end grain of of the strips will soak up a lot of epoxy so be sure not to starve the joint. It’s better to just gob it on thick, press the stems into place and wipe up the copious squeeze out after the clamps are in place.

Canoecraft recommends using screws to hold the stems in while the epoxy sets, but I found that using ratchet straps and strong rubber bungees worked very well and didn’t leave me with holes to fill afterward.