Today I managed to test the motor after tightening the belts considerably so they wouldn't skip teeth.  I had to hammer the pulley on the shaft to get the higher tension, so an adjustable idler pulley on each belt may may more sense in the future.    The motor draws only 5.4 amps at 13 volts or about 70 watts of power.   The boat speed is similar to sculling cruising speed (less than sprint) at about 1 knot.

This may seem slow, but it's already plenty to maneuver in harbors and to break out of wind holes back into wind again.  It is also much less power consumption than I expected.  I had hoped to achieve this around 100 watts, so it seems the low friction ceramic bearings, high aspect ratio large diameter carbon propeller have paid off.

The next step is to try a smaller reduction ratio on the initial stage which uses 20 and 120 tooth pulleys.  So maybe a 100 tooth or even 80 to boost speed.   Another option would be to print a 30 tooth instead of the 20, as a 30:120 should be slightly more efficient and less stressful than a 20:80 even though the ratio is the same.

Another way to increase speed will be to use a higher voltage battery which I eventually hope to obtain.