S/V Oasis is going to convert to electric motor from Universal diesel Engines and Such Forums

Ok you need to document this really well. that will be a great project that a lot of others will be really interested in.

Ok... I am going to throw in a few comments and observations here. they are worth as much as you have paid 🙂

Batteries

The batteries.. those are some nice batteries... Right now the iron phosphate lithium are the safest, most cycles, highest discharge batteries out there that are in production that any consumer can get. They also do well in a warmer hotter environment without damaging themselves due to overheating. They and this is the biggest thing don't thermal runaway and catch fire like some of the other lithium chemistries. Price does hurt but they will probably last the rest of your life.

I have seen some people that have used them from https://lionenergy.com/

The manual for their 100ish amp hour capacity 12volt unit has a minimum 3500 discharge cycles under abusive charge discharge conditions. But if you baby them much higher. I think the 3500 is their warranty cut off. I have heard but cant find on their website that you can expect about 10,000 cycles out of them. I will say that since I first heard about them their site has gotten much slicker and the details about the batteries has gotten much less. Not sure what that is about. A bunch of companies make them though..I was just looking at some made by Victron and I like them as a company. I have several of their battery monitoring products on Valkyr for the current battery bank.

Solar

How much solar are you looking at? we have 500 watts on Valkyr. 225ish watts on the hard dodger and 190ish over the dingy davits.  It has worked well for us. I have thought about expanding capacity some and the only reasonable place I can think of is some external to the rear railing around the cockpit that folds down on the outside when underway sailing but can be pivoted up at anchor or even when motoring. I figure you could get another 500ish watts on her maybe 1000 if you worked it right. If you stayed with really high efficiency, my 500 watts would be closer to 750-1000 watts. My panels are nothing to write home about  with the ones on the cabin being less than 10% efficient and the one on the dingy davits probably closer to 14%.. Good ones are pushing 20% nowadays. That is an expensive battery bank... for 300 amphr at 48v in LiFeP04 thats right at 10,000.. if you have a supplier for a better price than that you need to share 🙂

with 1500 watts of solar.. your theoretical charge capacity is 31.28 amps at 48volts. realistically a great day might get you 20 amps. One thought is what speed can you get with a 20amp current to the motor. If you balance it right you could run the motor sailing or not right at a neutral charging rate so that your battery bank stays charged and you just use the excess charging capacity to power the motor. Lots of interesting ideas 🙂

ok... pricing for solar is high if you just hire someone to do a turnkey job for you.. However you can get solar panels for 21 to 50 cents a watt from http://sunelec.com . they have a lot of factory second (cosmetic not functional issues), overrun, projects that they bought out the excess solar from etc.. even some used panels in good condition. You will have to dig to find exactly what you want in the way of voltage and efficiency. They also have new panels at still great prices 1 to 3 dollars a watt.. I never look at those much but if you really work hard on getting top efficiency panels that is probably where your going to go. I just looked and they have some 360 watt hundai panels for 49 cents a watt right now that are 18.5% efficient..  Those are some large panels (40x77 inches)so depending on layout maybe bigger than you can find space for. They have several brands right now between 32 and 50 cents a watt. They also have good deals on charge controllers and other stuff sometimes. I have found that they suck for support, even sales support but for that pricing it has been worth dealing with them for me. Another note on solar.. some of your panels are always going to be shaded. So you need to design the system such that it minimizes the negative effect of any individual panel being shaded. Here are a couple sites with a little about that on the linked pages https://blog.aurorasolar.com/shading-losses-for-pv-systems-and-techniques-to-mitigate-them/  https://thosesolarguys.com/does-solar-work-in-the-shade/

Generators

For long range power you need to up your generator, I am not a gas fan on the boat but it is what it is.. ether get a 4+kw diesel gen or stick with the 2kw gas and get two of them such as the honda's or other brands now that are quiet and stack/plug into each other to work in conjunction with each other. Sounds like you could get about 5 knots with 4 kilowatts of power. Something you could get one generator and add one or more later that will stack to spread cost over time. Gives you much larger capacity along with some redundancy.

I think if you push your solar as much as you can and also maybe look at some wind that you are going to be doing well. Direct drive connection to shaft is going to be simple and quiet but honestly im not sure about efficiency or heat generation. That is a lot of torque at low rpms. Most electric motors are a lot happier producing at higher rpms and then gearing down for the prop shaft. High power and low rpms also seems to me that it will produce a lot of heat. I haven't really been keeping up the last 5 years or so with the state of the art but last I looked that was my impression on what was available.

Overall power?

as far as power.. 20kw = 26.7 hp in applied power. The 32 came with a 24 hp engine and some upgraded to 27 hp... I would expect that with that electric engine that maneuvering and speed wise it will actually exceed the performance of a diesel all around other than as a system for range. Considering we never really use full rated power I would think it is going to work well. I'm not sure the difference in the 32 vs the 38 for hull speed from personal experience. I would expect for our 38 that that 20kw would get us to about 6 knts. with the 32 hp diesel we can push 7.4 to 8 knots on flat water. You will find that the boat will move like a champ from a stop as in take people off their feet at how much torque it can produce if you just go to full thrust. I would think you will go to a larger prop also which will make it even worse. Make sure the thrust bearings are beefy on the shaft. it will exceed by a lot what a stock engine can do.

if you have generators 2x2kw and 1.5kw solar.. just on them you can produce about 7-8 hp so about 1/3 power just under those conditions. I would say that using that plus the battery bank could extend your normal speed cruising range by 2x or more for motoring in high currents etc..  (what is your expected full power range with that setup?)

Regenerative

Um.. regenerative power is a nice thought. but i wouldn't even use it as a consideration.  I have never heard of anyone getting any usable amount of power out of regeneration other than catamarans that run 10+ knots under sail. You could probably get a decent amount out of a large tow behind generator setup designed for power generation at 2 to 5 knots of speed. I think it would be pain in your butt to manage though. Lots of moving parts and connection points with huge loads on them. A couple 250 to 500 watt wind generators that you just mostly ignore all the time would be a better return on investment as in cheaper and less hands on work. downside is constant background noise from them.