I got myself a used Minn Kota 40. It is a hefty beast, almost as heavy as my 2hp Yamaha. I might yet strap it to my kayak but in the meantime I did a few test runs on a Miracle dinghy.

First outing was in a 15kt wind. With my weight in the stern and no tiller-extension the boat trimmed bow completely out of the water. The dink was impossible to steer at anything less than full power.

Second outing was in ideal conditions and I managed to get some good speed and power measurements. A pvc pipe sufficed as throttle/tiller extension.

Power was from two 22Ah LiFePo4 batteries, hooked up in parallel to three 50W solar panels. With the sun not very high and no mppt or buck converter, the panels only provided 70W.

Speed and power results:
2.2kts at 125W (speed setting 2)
2.6kts at 170W
3.1kts at 200W
4.2kts at 360W (speed setting 5)

The top speed is already on par with my Yammie's performance at fast cruise throttle, i.e. noise just above being tolerable!

Next up will be a series of modifications to improve the motor's efficiency. Shaft fairing, prop spinner, new prop etc. I have not yet looked at the throttle electronics, perhaps a pwm speed control might be needed.