I printed a 90 tooth pulley, improved the alignment, and the motor spins faster with the 11.25:1
ratio down from 15:1 previously.

The power consumption increased to 120 watts which is barely more than a single solar panel.   The boat speed 2 knots.   It will be interesting to try higher voltages and power levels but the efficiency is currently around 50% vs 20% for a typical electric trolling motor.