: I took a couple of paddles I made to the pool tonight, both seem to work OK
: but one is a bit soft in the blades, any thoughts on routing in a spline
: of fir or spruce to stiffen them.

Why not glue on a spine? Structurally it would make the blade resemble a "T" beam.

Take 2 pieces of 1/4 inch cedar strip -- or pine or whatever -- whittle and sand it to match the curves on the back side of the flexible blades and the base of the loom (where the blade attaches), and glue it on with some epoxy resin. You can easily, and quickly, remove a lot of the material with a handplane, and work the strip down to where it is giving your blade the reinforcement it needs. As you remove material, knock off the square edges of the strip and leave a rounded edge.

If you start with a 1/4 by 3/4 strip you may end up removing most of it, so maybe you'll want to rip that down to 1/4 x 3/8. You'll probably only need pieces about a foot long. If you don't have extra strips around (some of us actually DO clean up our workshops) head over to a lumber yard for a few feet of pre-milled half-round from their mouldings area.

Working with a wood strip will allow you to finetune the stiffness, but if you just want to make the thing stiffer, just use some epoxy to fashion a ridge of glass fabric or tape along the back of the blade. A piece of paper, neatly creased, will serve as a form.

Or, you can use some epoxy to glue on a tube made from carbon fiber. You can get this from a broken fishing pole, or buy a carbon-fiber arrow at the local sporting goods store. If you get one about 26 to 28 inches long you can rip off the feathers, cut off the point and the nock, cut it in half and have two pieces that are a bit over a foot long. You might even be able to find a plain shaft (no feathers, nock or point on it) for a bit less $$$.

Hope this helps.

PGJ