Tommy,

The sliding stroke takes some getting used to. It takes more concentration and, for me, slows my cadence a bit. If you're thinking of this as primarily a spare paddle I would recommend a length as close to that of your regular paddle as you can store on the deck. I don't have experience using a storm paddle for extended periods.

As to the biomechanics involved, it didn't feel any different to me from the motion with the full length paddle. You are holding the paddle in essentially the same way once the paddle enters the water. The only difference is that your pushing hand is applied near the end of the blade (how near depends on the length of the short loom) rather than at the root of the blade.

If I were actually using a storm paddle is serious heavy weather I would feel more comfortable with some kind of leash, but that would require a loom long enough to allow room for the leash as well as one hand hold on either side of it.

The idea behind the storm paddle is that the blade is just as large as that of the full length paddle, so the power which can be developed should be the same.

You might want to borrow one from a fellow paddler and experiment a bit before comitting to a purchase or a carving.

Len Thunberg