That's asking an awful lot from a 5kw motor. I would go with at least a 12kw motor like the ME0913 or similar and a 72v or even a 120v system to make sure you can make your required speed. Doing almost 5kt into that kind of headwind takes some power, and 5kw is roughly only 6.3hp if you dont mind sort of an apples vs orange conversion.
FWIW I can make that speed in my 7600lb CAL 2-27 no prob in calm, with a 5kw motor at 48v with a 3 blade 14x10 fixed prop. Haven't tried against that kind of headwind yet. And you are significantly heavier and with a 2 blade folding prop. The range will be a problem. Lets say you have a 240ah 48v bank. Due to Peukert effect, lets say that means you can pull 100a from the bank for one hour before you have discharged down to 50%. I am just pulling those figures out of the air btw but it sounds about right. Lets say with a 48v controller you need the 100 amps to make that speed. Your run time at that power level with that size bank is one hour. So you need twice the size bank that many people would install on that size boat. What this means is that you will probably need to go with LiFePO4 batteries, for reduced Peukert effect and greater depth of discharge. Maybe you could get by with say a 300ah bank at 48v. You get slightly better efficiency at higher voltages, so maybe you go ahead and go with a 96v system, and maybe only 150ah or so of capacity. Well, that is still nearly 15kw/hr, a very expensive "gas tank" for your boat, using state of the art cells and BMS.
This can be done, but like I said, you are demanding a lot from the existing technology and it won't be cheap. The motor and controller, yeah, pretty cheap. The battery, quite expensive.
I want to add that the 12kw motor for a given output power does not consume significantly more power than a 5kw motor. At least I couldn't detect it. I got the same speed at the same current with my ME0201014201 5kw motor as I did with the ME0913 12kw motor. I detected no difference whatsoever. The bigger motor is still pretty small. It bolts right up to the same motor mount plates or gearboxes. So the only reason to prefer the 5kw motor is it is a couple hundred bucks cheaper, and that's small potatoes compared to what your batteries will cost.
I dont think much of the Chinese gensets. Many users report very short working lives from them. The price is right, yeah. I would love to have a 10hp diesel new in crate for $1000 even without a generator end. The fact is, they dont hold up well and rebuilding is apparently not practical. Might make a good emergency backup genset that never gets ran unless the primary goes down, maybe. But for cheap, you are kinda stuck with a gasoline portable unit like the Hondas which btw seem to hold up fairly well. Mike in Bianka loves his little 2kw unit. But you will be pulling (again, imaginary figures) at least 5kw from the batteries at required speed, so ideally your genny will be rated for about the same continuous load. This would enable you to operate with a more practical sized and economical battery bank.
If you dont mind going with a 3 blade prop, you might increase your efficiency considerably. Drag can be reduced by turning the throttle a bit so instead of a regeneration drag, it freewheels. If you barely expend power instead of staying at the power neutral point, you can reduce drag to zero for VERY LITTLE draw on the batteries. Like a couple of amps or less. At one amp I actually make 1.3kt lol.
The expensive part, like I said, is going to be the batteries. The motor, reduction gear, controller, etc will only cost a couple thou at most. So here is one thing you might do if you are not in a big hurry to get this thing racing. Go ahead and repower. Optimize your prop and reduction gear. Install a small bank just for the purposes of testing. Maybe go with cheap golf cart batteries, like I did, and get 10.5kw/hr for less than $1k. Get some performance data graphed for your boat and figure out from there if you want to go with a higher voltage and how much storage you will need. The flooded cell bank becomes a reserve bank to your new main bank of LiFePO4 cells. Either that, or just can the whole project and install a Beta diesel instead, before spending thousands on high tech batts.
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