Have you made any other changes to the boat
recently? Looking at the performance graph from Jefa, it appears that the output torque would have to be in the area of 70 kg/m (over 500 ft lb!) to blow that fuse.
So, I would think there are three possible causes:
Boat seriously out of trim in heavy wind/sea state
Internal problem in the drive, check the planetary gears, clutch
issue, additional resistance spiking current
I doubt your boat is the problem, it would be very noticeable when not using the drive. Internal problem is certainly possible, but my money's on a bad electrical
connection. Check for corrosion
in the male and female connectors, both the plug
and socket contact the point of connection of the individual wires to the contacts. I had an intermittent issue with my Autohelm
GP tiller drive that was solved
by replacing the connectors.