Electric final drive

One advantage of a diesel electric is that the diesel can be placed anywhere that space is available and the actual drive motor is relatively small compared to the diesel. We owned a small sailing cat for a short time that used hydraulic motors to drive a prop in each hull. The diesel to drive the hydraulic pump was in a locker at the back of the boat. The hydraulic motors where maybe 12" by 12", very compact.

I agree with Marmot, on a vessel this size (44'), going electric makes no sense. I also see sailboats motoring 80% of the time, even with favorable wind, I always see them motoring and no sails up, which I don't understand. I'm guessing they're doing it to charge batteries as well.

But why don't they just put a generator on most 44' sailboats? It would make a lot more sense to run a battery charger to charge the batteries, and have the refrigerator and hot water heater and etc on AC power while the generator is running, then everything running DC and then using the mains alternator to charge and try to get the battery bank up. You could be sailing along with just the generator going, or if you want propulsion assistance, sails and main running and no gen.

There is a sailboat around 50' running around Fort Lauderdale with just electric power, it has no sails and a TON of solar panels. Supposedly it cost less than $10,000 to do and has done 2,000 NM's . I've seen it underway twice, once I passed it in Palm Beach and another time in Fort Lauderdale. But it only pushes the boat 4 knots, he also has a diesel that he can run to push it 6 knots, so it's NOT entirely solar powered per say.

http://www.sun-sentinel.com/news/fl-amendment-1-solar-boat-20161101-story.html

There are boats that just sail when the wind is good and sit when it isn't. They can get by with a generous battery bank (hundreds of pounds not thousands) and some largish solar panels. Motoring is more convenient that sailing but if you are committed to sail then really motoring and thrusters are for maneuvering in crowded anchorages and marinas.

There are a number of people here that cruise the world with sails, electric motors and solar panels: http://www.cruisersforum.com/

I had a diesel electric tug. I liked the setup, but not affordable for private use.

Here is a video of a Diesel to electric sail conversion. He has about 15kw of power and a 200 Ah bank of 8 6v in series for 48 v.

If he drains the battery he can probably get an hour of propulsion. 20 minutes is more reasonable from a battery lifespan perspective, and if he has 300 watts of solar (functionally) dedicated to the propulsion he can do that 20 minutes of maneuvering under motor every sunny day.

An envelope. However, if you watch part 2 he talks about throttling back a knot or so to get 4 hours out of it.

Edit: To be more specific about that envelope. 200 amps at 48 volts is 9600 watts. A motor that is "virtually the same" as a 12 hp diesel is going to ab about 9 kw (since a kw is about 1.34 hp). Fudge in a bit of inefficiency from internal resistance of the batteries and fudge a bit in the other direction because high quality batteries should hold a bit more than their labeled charge and an hour seems fair to me. So 20 minutes of full throttle and you have 3 kwh of electricity to replace. 300 watts of solar performance for 10 hours in the day and you are back to charged.