Welcome to the forum, sailmed...

My first question would be how often you ran that 135hp engine at full throttle? My second would be, do you know how much power it would take to get you up to hull speed? Anything above that is pretty much wasted (oversimplifying, of course).

This application seems ideal for some sort of smaller size AC motor setup, either induction or brushless DC. The Curtis 1238/AC-50 combo seems like it might do the job, and allow you to recharge the battery pack while under sail (assuming you have excess sail power above and beyond what it takes to reach hull speed).

 

Jeffrey's on the right track for sure. If you're able to get up to a good clip under sail power, you could "regen brake" for extra generation back into the pack, assuming it doesn't put too much drag on the ship.

Since you mention it was a 1500 lbs engine at 135 HP, I should probably assume it's something like a Detroit 4-53, which is a heavy beast that doesn't make a lot on the HP scale but makes lots of torque which is really what a ship or boat needs to move the screw/prop/impeller/etc.

In that regard, electric could be a good fit, since it can make a lot of torque, even with a low continuous horsepower rating.

The real thing is... when you find yourself in calm conditions, how *long* to you typically run the engine? You mentioned 250 hours in 15 years. My thought is that with the removal of the heavy engine, you could add more batteries to keep the ballast of the ship correct, and gain more runtime from the electric setup.

Otherwise, if you're just pulling from your trojan house batts, you may find yourself running a while and then having no electricity until sun-up or the wind picks back up again.

It should definitely do you well for moving into the dock or anchorage, but the real question is would it keep you moving long enough/fast enough in the calm to make it worth it?

Edit: Completely forgot you mentioned the 8kw genset, which will definitely help if you run the batteries too low.