Has anyone went from diesel to electric propulsion?

There is no such thing as a free lunch... 50 KVA equals about 55hp. How fast do you think the boat will go on 55hp?

Good thing you're not interested in speed, cause you'll be lucky to even move out of your slip. I also don't see any savings unless you can find buyers for the motors and gens you'll be replacing (extremely unlikely). Then there's the cost of taking everything out and for designing, buying and installing the replacements. If that 70' Italian sport boat is getting too expensive I'd suggest selling it and buying a more economical boat. In fact if your desire is to go electric you could look at one designed from the ground up for that. As an anecdote I checked into going solar with my house awhile back. Once I cut through the salesmanship the bottom line was that I wouldn't save a dime for 20 years, at which point it'd be time to replace the system. The technology just isn't there yet at a cost that would work. Since speed isn't a consideration may I suggest going to sail or a trawler on your next boat.

For more information on related topics I suggest you look at some of the posts and threads by YF member Brian Eiland.

First let me point out that HP output at the motor is much different than what is delivered to the props.
Second: "Performance may vary based on operating conditions. The figures provided above relate to travel at between 60 – 80% of hull speed."
Third they don't mention torque. I have doubts those motors could even move a 50T yacht, and good luck maneuvering.
If you'd like to cheaply experiment mount a 100hp outboard to your swim platform and take it for a ride. I think with the smaller props that'll closely mimic what two of these will give swinging your props.

You want to do this because the MTU's "are way too expensive to run"? Even if you can find something that may work (doubtful) what do you think the pay back time is going to be vs running your MTU's? You won't get there in 3 lifetimes.

Actually I think you under estimated that. I'm thinking 5 life times.

actually electric motors deliver peak torque at very low RPM.

May I ask you which one?
The boat in your Avatar has a Cantieri di Pisa flavour, but I don't think that's what she really is.

If you run your yacht at 8kts or less you will get real close to 1 nautical mile per gallon. If you run slower than 8 you will achieve even better fuel economy. There are a number of advantages of running at slow speed and in my opinion the popular thought of damaging your engine my running at low rpms is not accurate as long as your engines achieve operating temperature.

Speed issues? I think the problem is maneuvering the boat with the 12" props you'll be spinning on the 3/4" shafts. You can make the boat move with little horsepower. Once got a 42' trawler back to the dock with a makeshift bracket for a 2hp Seagull. We went onto an open face dock with one shot to get in. No chance we could have maneuvered her into a slip.

Siar Moshini.

May I ask where you're getting your fuel numbers from? If they were even close to what I'm getting, I wouldn't worry about it.

Hang on, are you Rocketpip with a new username?
If not, I can't believe that we have two persons here who know about this boatbuilder, because even here in Italy I don't think there are many boaters around who ever heard of it!

Not that I'm dismissing it, mind.
Even if SIAR-Moschini was only active for a short timeframe, Mr. Moschini (that's the right spelling by the way, not Moshini - with the unintuitive pronounciation 'Moskini') is considered as one of the historic fathers of the Italian boating industry.
Among other things, Custom Line of Ferretti fame was actually Moschini's brainchild, before Ferretti Group took over.

The boat in Rocketpip avatar must be the 21 Coupe, I suppose?
Extremely rare indeed, if not even a one-off, I'm not sure.
Anyway, frankly speaking, that's not an ideal platform for the type of conversion that you are envisaging.
She was in fact built with a military-derived design, and meant to keep going fast(ish) also in the rough stuff.
The MTUs were obviously consistent with the overall design.

But if you (and/or Rocketpip?) will decide to go ahead, all the very best for such BIG project.
I for one would love to see a regularly updated report about it, possibly with photos.
And since I don't think that 30 years ago or so the builder labelled anything onboard with other than Italian, if you would need any help with the translation, don't hesitate to ask. I don't think there's much more I could do to help from here, because the company doesn't exist anymore - but happy to do whatever I can anyway.

well what fuel burn are you getting?

I ve run a few boats in that size range over the years and at hull speed of 10kts, average burn will be between 16 and 18 gph.

now if you exceed hull speed by even just a knot, say 11kts you fuel flow will jump to around 30gph... at 13 to 14 kts you will be burning close to what you lll burn when fully on plane but at a fraction of the speed.

as Fred suggested, slow down even more and you will save a lot of fuel, indeed easily hitting 1 nmpg. Problem is that as such low speed, your big diesels are going to be running too cold.

I haven't actually enough time on her to know the difference but I will take your advice and try a bunch slower.
Keeping the temp in mind.
Thanks

I just got back from a fishing trip down to Mag Bay Mexico leaving from Newport Harbor. The boat I was a seventy foot Mikelson with 3412e Cats, 1450 HP each and will push the boat at 28 kts. Cruising at 20 kts this boat burns close to 70 gallons per hour without the added gear. The boat, for the trip, was loaded with gear and suppliers for 3 weeks for 6 guys and an extra 330 gallons of fuel on deck. We ran to San Diego at 9 kts for time reasons and topped off in San Diego and took on 130 gallons for the 65 mile trip. Then we left for Mexico at 8 kts with genset running, travelled to San Benitos Island, Alijos Rocks, Mag Bay, out and back fishing for 10 days then the run back to Newport Harbor at a distance of 1600 Nm on 2200 gallons total. These figures do not include all the miles trolling for Marlin and the genset ran the whole time. Specifically we ran 280 nm from San Diego to San Benitos Isl. where we topped off the tanks to clear the cockpit of the barrels and took 300 gallons for this leg of the trip. So .933 Nm/g including the genset which we estimated to be about 1 gallon per hour.

Concur. I run 11 and burn 26. I could drop to 9.5 and cut the 26 down a third or perhaps more. Problem is the lack of load on the engines. Hence the 11 knot target to spend a bit more in fuel and a lot less in maintenance.