Repower with Electric Drive?

Hi, without going into details, I think your boat will be worth twice the money at ten times the cost. Whatever, do the financial math to start with...

You might want to bounce the idea off this company:
https://www.duffyboats.com/

Yes, it can be done: Current tech is up for it, but not reasonable cost.
Maybe $50k for a good instal, but short range. (WAG)
Since you are going in that direction you might as well add solar panels with the latest in chargers and technology, add another $10-15k

No apologies needed even for bad ideas.
It all boils down to cost and your bank account level:
Great idea, but not cheap.
You can of course go redneck and install old golf cart motors and controllers with 50 golf cart batteries, say four 5HP motors with 4 shafts...

On a steel hulled boat. That could be interesting to control in high current or wind.

What about a single 4 stroke outboard. Can be very quiet and probably cheapest route. If going electric, the only way I'd see it as feasible IMO would be diesel electric. 20kw diesel generator and a good amount of battery banks. Could even somehow rig the generator to turn the shaft and bypass the electric to get home if needed. You have a lot of current there, so will need some power.

Wouldn't do much to solve his main issues, "It has the original fuel tanks with corrosion and sediment problems, so I'm looking at needing to replace the tanks and .....eliminating the fuel and exhaust smell, and refueling at my slip overnight".

Well, it is true but the most reliable and straight forward method (4 stroke) and could go with a much smaller fuel tank. Diesel electric, depending on how many batteries you put, wouldn't have to run the generator all of the time, but could run the generator and battery charger and greatly extend your range, also with a much smaller fuel tank than what's in the boat now.

Elco has a number of drive system from 10hp to 100hp equivalent. Nicely done but not cheap

https://www.elcomotoryachts.com/learn-electric-inboard-motors/

I had looked at it for the 26’ gaffer I built a few years ago. Instead I went with a more basic kit from Thunderstruck EV. It s ok as we only use the motor occasionally to get on or off the mooring if it s gusty or to dock.

another issue with electric is that batteries rarely last more than 5 years... $$&&

I've seen a couple of sailboats with electric motors. When I was in San Diego a guy a my marina had his converted to electric, it powered it okay. However; his range was not great and it took all night to charge it. He had added panels and a wind generator but they were not even close to the charging power he needed to recharge the batteries after a days sailing. He had a 42 foot Island Packet sailboat, not a 32 foot Roamer that he had to use the motors continuously for all day. He did this around 2013/2014, I don't know if the batteries have improved that much since then.

I wonder what depth of discharge to the batteries their ranges are based on? I’ll bet pretty deep. I see they list a continuous operation with a generator. Curious if they do this with a big ac to dc converter? Or a direct drive dc motor on the PTO of the gen? Got me thinking, this would be an interesting trolling arrangement vs running and listening to a main engine idling with a trolling valve bypassing clutch pressure to be able to go slow enough. Hmmm?

Ummm, not to sound like a simpleton, but...
Why not just run two marine electric motors of a deisel gen? The gen would charge a "normal" set of batts to power the boat electrics. Why the need to go silent and run just off batteries at all?
Thought about this myself for my 38' Regal; just not yet there.

Because when you do the math you need BIG generators to make enough juice...

It takes KW to move things. KWs come from gas, diesel or electric motors.
Batteries must be recharged from gas, diesel or electric power grids.
Power grids make KWs from gas, diesel, coal or oil.

Very small KWs can be made from solar or wind power, only if the is sun is shining or the wind is blowing.
I would call this near worthless on a practical boat.

With this picture in your mind, the most cost-reduced way to move a boat is the way it came from the factory.
Most of us will be long gone before any (if any) payback is ever realized.

If your thinking of a diesel / electric plan like a train locomotive, these are out there in big boats.
Not necessarily for mpg, just better control of the propeller rotation and a very flat & tall torque band from one to hundreds of shaft rpm.

Not to mention the fact that batteries are quite heavy. Unless you go LiFe.... Very doable to fill the space the tanks were in with a LOT of KWh..... it's just $$$$$$$ Some people buy electric cars off the junk yards to play with the batteries. Some knowledge required.

At the lake where I usually sail, only electric boats are allowed. Main brands are Torqeedo, Aquawatt, and Aquamot. All of them offer inboard solutions. Most of us use solar chargers to "fill up" during the week and use it on the weekends, as we are "off the grid". Sure, many, specially powerful ones, ore not cheap, but: zero maintenance costs, no fuel, ...

@batteries: a 5kWh batterie is about 37kg for about 5000€ incl tax, charger ~800€ (quickcharger ~2000€)

You need a Hinckley dasher!!!!!

True this. Big DC motors will need (very roughly) 1 amp of 3 phase power for every 1 HP. So a 300 HP motor is going to need around 300 amps of 480v. Or about 150+ Kw from a 3 phase genny. So you'll need around 300 Diesel HP to run that 300 Hp electric motor without batteries....because any imaginable battery setup isn't going to keep up with that consumption.

I think I figured this correctly...

Ok, anyone with experience using or maintaining the Torqeedo Deep Blue system? Seriously contemplating a tender repower.

A friend of mine has one on a tender on a yacht they run. They work good. Range is a little limited with one battery......it's good to go to and from shore a couple of times.