So, hypothetically...

Lets say a 20 hp motor, and it is going to cost you around $13 to $14k installed. You might also need to replace the prop and get the stern gear sorted at the same time. Some would say 16hp is enough, but that does not put a big dent in the cost.
Once done, you need to work out what the boat would be worth. The classic logic is if you are going to keep the boat for many years, then a bit of over-investment is justifiable.

Having just done a repower for a 30 footer it will be $20k to $25k to do properly.
Price difference on a 18hp vs a 27hp was stuff all as was the weight difference (about 18kg)
At 6 ton I would go 42hp.
Engine beds, electrics, fuel tanks and related stuff like sound proofing was the difference even where the engine deal included pong box, mulfler and pipes.
The best of material where used like V-bar sound proofing and Vetus hoses etc.

So, at present she has 8 x 210 ah AGM batteries on board. They are located under the quarter berth and under the cabin sole (not a fan of the latter location).

There is the port side cockpit locker and lazarette available for, perhaps a diesel generator as some folks have suggested.

At present, there is no solar or wind. With my lame European skin, it is essential I put a bimini on (purists please don't hate me ). So, with the frame I can look at solar and wind options. Would that be enough, though? Or would a generator/hybrid system still be needed for long-range?

I'm interested to hear opinions of what you guys would consider as a fair offer to make? Perhaps by PM so as not to ruffle feathers.

In my opinion the boat is highly problematic, as you point out it has no solar or wind or indeed any form of power generation. Apart from the motor there is a powered anchor windlass, Raymarine electronics package with AutoPilot plus any other powered devices, including lighting.

It is fitted with a Porta Potty, while Porta Potties may be alright for day sailing I don't think it is the kind of situation that you would want to deal with on a longer passage. A fixed head and holding tank may need to be allowed for.

Hit him up at $40k or even lower if you're feeling cheeky and see how much he baulks. No way is it worth anywhere near $55k which is why he has said 'negotiable'.

Says it's done two Atlantic and one Pacific crossing, ask it that with the electric motor in place. Here for you entertainment and education is a spec sheet on the motor. Cruising range* 34 - 19 nm, hope it never stops blowing.

https://www.elcomotoryachts.com/ep-20-inboard.shtml

" No way is it worth anywhere near $55k" that statement may or may not be correct

" I wouldn't value it above $25K." you probs wont own the yacht then

The main factor is the distance of your passages. If it's only a matter of getting out the heads that's fine but if the electric motor is using 50 amp hours I think you batteries will be well flat after a hour or so. Rather have the diesel to fuelled and ready and keep the battery/solar for house.

Forgetting about the boat and what it may or may not be worth, how about thinking about the energy required to move the vessel when wind is not what or where you want it, i.e 90% of the time.
Forms of energy:-
1. Heat energy, from the Sun or burning a chemical.

2. Chemical energy, from a chemical reaction between two elements such as carbon and oxygen which when catalyzed by spark or compression will ignite and convert to heat energy which when contained causes pressure.

3. Electrical energy which usually requires both of the above to make it happen.

4. MECHANICAL ENERGY which is what you really want to make that shaft rotate and the propellor to bite the water and push your boat along.

The mechanical energy required to push your boat along at hull speed for a given amount of time is a FIXED FIGURE and can be calculated in terms of horsepower, kilowatts, kilojoules, British thermal units or what ever.

So the viability or not of electric propulsion does not come to an opinion on the "green-ness" of it or any other opinion.

It is a scientific CALCULATION!!

The boat is designed with a certain amount of it's displacement in a certain location to be devoted to the means of propulsion and the fuel ie "STORED ENERGY" to power the means.

Therefore if the boat was designed to carry a weight of "X" being a combination of means of propulsion and fuel to carry it a distance of "Y" (anything less than 100 nm would be foolish), one needs to do the calculation to determine which method of propulsion come within the design factor of "X". Don't ask me to do the calculation because I know in my bones what the answer is.

One of the first laws of physics is that "Energy cannot be created or destroyed. It can only be changed from one form to another."

Simple analogy:- Compare an electric stove to a gas stove.

The electric stove requires CHEMICAL energy, converted to HEAT energy, converted to MECHANICAL energy, converted to ELECTRICAL energy then converted back to HEAT energy with losses all the way down the line.

The gas stove has CHEMICAL energy which you light to give you HEAT energy.

Have you got the picture yet?? Neuclear reactors have not been miniturised yet.

I am good friends with some very experienced sailors who went electric. They persisted with it for some time and are technically very talented but the lack of ability to punch on in sloppy conditions or motor for long distances led them to replace the, rather expensive, motor and go back to a diesel.

On ya Cisco.

All this hypothetical crap from people's personal opinions.
Have a look at sailing uma on you tube they are live aboard cruiser and have electric and give honest opinion.

G'day Selkie,
As you know, the one constant you can rely on is you will ALWAYS motor more than you planned!
Re: electric or other, it all comes down to the intended use doesn't it? If you're swanning about the bay with assistance all around you, who cares? If you're planning on going to NZ or South Pacific, I'd be researching the pants off this subject.
Best of luck to you mate, I hope you're enjoying the shopping!