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You have given this a lot of thought. I am a marine systems tech, who sailed away from Victoria, BC, in 2011. Made it as far as New Zealand, before running out of money. Now planning to sell the boat, and return to Canada.

I am at the hypothetical stage, of planning a car conversion, when I get back. (And maybe a boat conversion farther in the future)

Either the Hyper9, or AC50 would work. I like the Hyper9, mostly because they have a matched controller, and the higher voltage adds to efficiency.

I think keeping your gearbox is a good choice, for your application. What is your current engine's cruising RPM? If it is a Lehman or Nissan, I'm guessing around 1800 RPM.

24" pitch sounds like a lot, but I am used to smaller boats. I would suggest getting the batteries and charging system figured out first, followed by removing the diesel, and fitting the motor.

Worry about the prop after the boat is moving under electric power. As it is a feathering prop, you can adjust the pitch after you get a sense of the performance and have real world RPM to base things off. Prop calculations are complicated, requiring assumptions that affect the result, but may not be accurate. Most 'prop guys' can tell from experience, what the pitch should be, from the basic boat stats. Knowing your actual motor RPM and your target RPM, should allow you to get the correct pitch, without too much trouble.

Check out Will Prouse on Youtube, DIY Solar Power. He reviews a lot of different lithium iron phosphate battery manufacturer's products, often cracking open the case, to inspect the internals. He also discusses battery management systems.

If you are considering a battery pack, from a salvaged EV, take a look at Damien Mcguire's Youtube channel, EVBMW. He gets into the fine details of hacking and repurposing EV systems.

My general impression is that putting together a propulsion system with something like a Hyper9 and lithium iron phosphate batteries is expensive, but reasonably straight-forward. Using a system from a salvaged EV can be pretty inexpensive, but tends to be complicated, especially for those of us without knowledge of CAN bus.

I'm not sure a diesel generator is going to have the benifit that you expect. 5kW converts to an equivalent of about 6.7 horsepower. 5kW won't move your boat at 4 knots.

Your 120hp diesel is equivalent to a 90kW Hyper9. If you are running it easy, just over half power, at 50kW (67hp), you will need 50kW hours of capacity, for every hour of range that you want. I can't see a battery pack of less than 150kW hours being practical.

And that brings us back to the question of new, or salvaged batteries.
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