Can you share with us how you use the boat (current and future intent) and why you are replacing an auxiliary diesel with electric propulsion?
Khaleesea is Hunter 29.5. She'll probably never leave the Chesapeake Bay, and she's definitely not a blue water boat, so range isn't really an issue. Even so, if my math is correct, I should get 5kts for about 8 hours with the battery pack I'm putting in (16kWh).
With the charger I'm going to install on the boat, I should be able to full charge from dead empty in a day-ish.
I am reducing the amount of pollution I put into the Bay.
I'd like for my boat to be as quiet under power as under sail.
Sailing the bay, I should be able to get a week out of the batteries, provided I'm not trying to travel directly into the wind. If I'm sailing most of the time, the regen should cover any house battery usage and then some. I won't know for sure until I start collecting data, though. That's part of what this is about - learning what works and what doesn't.
Electric motors are *far* more reliable than even the most robust diesel, don't need reconditioning, maintenance, or winterizing, and weigh far less. The motor I'm putting in my boat weighs 35 lbs, making it easy to replace if necessary.
I'm planning to retrofit a catamaran for a circumnavigation some time in the future using a similar design. This is the prototype. Better to screw things up with a $3k system than with a $30k system.
Lastly, I have a bet with a friend that I can outrun his 33' hunter under power once the conversion is done. Since I'm more than doubling the available HP on the boat, that should at least make me competitive.
So yeah, there are a lot of reasons.