Electric inboard motors

[jhaerle]

I've done some internet searching and I haven't come across any info that helps me out, so I'm hoping someone here has some experience or can at least direct me to someone who does.

I have a 1979 Chris Craft 28' Express Cruiser with twin Gm 181FL engines, which produce 130 HP each at 4600 rpm. The boat currently has 14x11 props, and Chris Craft recently told were originally 13x13 from the factory.

My problem is I live 18 miles across the local bay and it takes me 1.5 hours to make the journey. I average around 11 mph (GPS) against the tide. I only run the motors at about 3600 rpm due to their age (they are original, but have been rebuilt a few years ago).

I've been told that without more horsepower, I really shouldn't expect to get much more speed out of the old girl. The problem is in the current configuration, I don't think there is quite enough space to put even a slight larger engine, like a 350. I don't see the point in replacing the under powered engines with the exact same thing. So it occurred to me what if I could replace the engines with electric motors? There is plenty of room to mount a single larger engine to provide the electrical power to the motors.

Has anyone here ever done this? What is the equivalent size electric motor that could replace the engine? Can any of the marine electric motors be run solely off the power produced by an on-board generator that would be running the entire time the vessel in underway? Any thoughts on the matter would be helpful. It seems like this has had to have been done before. I think the only reason that would dissuade me from this is if the cost is substantially more than just replacing the motors.

[ranger58sb]

There are several threads on electric propulsion here on CF. Use the custom Google search tool; the normal search tool is pretty useless.

There was a thread on trawlerforum.com, couple years ago now, where a new owner was converting a classic diesel (Elco, I think) to electric -- with new propulsion components and system also made by the same company as the original builder (again, Elco, I think).

Her intent was to show the boat in various Concours d'Elegance venues, especially one on the other side of the Chesapeake from her docks, approx 25 miles distant. I think the outcome was, after the conversion, she wasn't confident that she has the range to make that trip under all circumstances.

I think her name was Star-something...

You could look at some of the Torqueedo info; they've been making larger and larger plants for electric propulsion... but they're pretty proud of their stuff. There's also the charging (genset?) and storage (batteries up the yazoo) issues too.

Back to your thoughts on replacement engines... I'd guess new engines of the same size would produce more (much more?) horsepower and torque than your older originals. And they'd likely be more reliable, too...

Diesel conversion might offer improvements too, but would cost even more and probably wouldn't add any significant value to the boat... other than your enjoyment.

-Chris

[StuM]

So you currently have 260 HP of fossil fuel propulsion and run at about 2/3 Max RPM which means you are maybe using 100HP (?).

Electric or dead dinosaur powered, you will still need the same HP. Which means a 100HP generator to drive a bl**dy big electric motor. Good luck fitting that into a 28ft boat.

(Basically you are talking about converting fossil fuel to electricity to motive power in place of directly converting fossil fuel to motive power.)

[Lepke]

Diesel electric isn't as fuel efficient as direct coupled. I ran diesel electric tugs and there's a lot of controls between the generator and electric motor. All of that would be a unique build for your purpose. I don't know your engines but they sound like 4 cylinder inline. The same length as a 350. I would think the shafts would be spaced enough to allow v-8 engines.
V-8s and higher boat speed might make your boat more valuable. There always seems to be marine 350s for sale. It's a common engine and rebuilt short blocks are cheap if you buy from a place that rebuilds.
Diesels wouldn't pay and weigh much more than v-8s.

[meatservo]

Maybe change your props for more efficiency?


meatservo

[valhalla360]

Unless there is a specific issue, take them up to 75-80% and see if that gets you on plane. Unless you have reason to believe there is a problem, opening them up once in a while shouldn't be a problem. Wouldn't want to run wide open all the time but if opening them up for 5min causes a failure, babying them isn't going to solve it. You will likely get the failure anyway.

Are you sure they are only 130hp? Are you sure the throttles and tachometer are right? You could be at much lower throttle settings than you think.

It sounds like the big issue is you aren't getting on plane. Quite possible if you've loaded up with a lot of gear and over time engines do lose a bit of HP. Or may just be that you need to give it more gas.

260hp should be enough to get most 28' cruisers up on plane. My brother in-law has a single big block with about that HP and it gets on plane OK.

A few options:
- Electric: NO, heavier, less efficent, more up front cost and expect resale value to be near zero.
- Sell and get a different boat: Unless there is some particular love for this boat, this is the most logical. For the cost of just about any of the following options, you can sell a 1979 boat and buy a boat 5-10yrs newer with engines that get the boat on plane without re-engineering the drive train.
- Look for newer 4cycl with higher HP (might have to be a V6). Either should fit and you should be able to jump up to 150-200hp per engine.
- More work to retrofit but a single big block V8 might work. HP will be similar but a single engine will likely be a good bit lighter which will make it easier to get on plane.
- Give up planing: If you aren't trying to get on plane, you don't need a lot of power. Most 28' sailboats are under 30hp total. A pair of 20hp diesels will keep the maneuverability and top out around 8-9kts and if you drop back to 6-7kts, will significantly improve fuel efficiency. Your biggest issue is putting enough weight in the back that she doesn't sit stern high.

[LoudMusic]

It's possible. How much money do you have?

https://www.youtube.com/watch?v=WZkXOfxiklQ