I have been watching several cruiser sailing channels on youtube and a number of them are converting their diesel engines to electric. There are expensive options out there for turn-key systems but several of them were able to use forklift motors successfully for much cheaper.
The decision was made because of the amount of maintenance that diesel engines needs, especially when dealing with sub-optimal fuel from random locations, as well as the cost of replacement when parts break.
This is a really good article on doing a conversion.
You know....
My dad just bought a sailboat with a 40" or 50" or some ridiculous number gargantuan sail. Since these sails are typically so gargantuan, I bet they'd make kick-ass solar collectors. "Solar Sailing"
Has a nice ring to it.
The problem is adding weight that high up would unbalance the boat and put too much stress on the rigging. Also being vertical the amount of power generated would be poor for the cost of the flexible solar panels.
All of the boats I see have several panels on the roof with a wind turbine or two on the transom as they can generate quite a bit of power for their cost.