You can’t compare a motocross engine or a car engine to a speedboat!

With a motorcycle, you only need 55 kW during acceleration, and the average power consumption is 5–10 times lower.
With a speedboat, you need constant power, and with 300 kW, such a large boat would travel slower than 50 mph, and it wouldn’t last more than 45 minutes because you can’t fully drain the batteries if you want to have them a longer time.
With this speedboat and battery setup, you won’t be able to go farther than about 30 km from the starting point if you want to come back at 40–50 mph; for lower speeds, it’s pointless to strain such a boat.

Questions to consider:

• For the intended speeds, is it worth using a surface drive and a clever propeller? In my oppinion it is better almost fully submerged standard prop.
• Is this boat–drive–center of gravity combination even suitable for a surface drive with the planned shaft angle? I think it will be very difficult to lift the bow.

In Germany, there’s MSA Marine Systems. Ask them which material they use for drive shafts. If you can’t find the answer, I can look it up—the material of the shaft is written somewhere in my notes. Material is almost the same like by Mercury, but with German material code.

I love electric propulsion, but its use in speedboats is very limited.

Well the travel distance could be a problem. That’s why I began this thread with asking about the Cigarette AMG Electric Drive. But unfortunately nobody have ever seen here this boat in water. Maybe Cigarette knows how far it was able to travel with one charged battery.

I wouldn't worry about distance yet. I would start with what each motor is going to draw at say, a 70% load. Divide your battery capacity by that and come up with a runtime. Take another 10% off for inefficiencies in power train. Are you left with a time you can reasonably enjoy yourself with?

Sorry to butt in, but there’s no magic wand here.

With 400 hp (300 kW), this speedboat will at best reach 50 mph, and if you have a 300 kWh battery, you can drain it in 45, at most 50, and not 60 minutes. Assuming you’re traveling at 50 mph (probably won’t exceed 45 mph), you’ll have electricity for about 60 km (38 miles).
In reality, the safe range probably won’t exceed 30 miles, or 50 km, and even that only in one direction.

Simply put, this means you’ll have a speedboat for trips within a 25 km radius, or 30 km at most, with a high risk of running out of power somewhere along the way.

I think you’ll need to implement forced water cooling for the motors, because they won’t be submerged while driving.
The motor and drivetrain will weigh at least twice as much as an Arneson drive, and together with the supporting structure, considerably more. This could pose a significant structural challenge, to prevent losing the drive during somewhat aggressive maneuvering.

The original idea of ​​an offshore power boat going from Miami to the Bahamas and back will therefore no longer be possible. But anyway the boat is in Germany, electric drives would make it possible to use the boat in the lake of Constance which is near to my home.

This is a Battery from the bike. 44 of these would be around 300 kWh. 600 18650 cells 20 in series and 30 parallel. Ten packs in series would make 800 volts. 4 Packs in parallel would then be around 300 kWh.

Actually the cool thing would be 44 x 50 hp = 2200 hp. So the battery is capable to produce Energy up to 2200 hp. Unfortunately the motor controller I want to use can only handle 2X 320 kW.

you may want to find a step hull,it will move easier thru the water.
who's motors are you thinking about?

Im confident it was never put in the water or planed off under its own power. If they tried it, it was a such a disaster they never said anything about it.

For the actual use of an electric drive in such a speedboat, you would need at least a 1000 kWh battery with a maximum mass of less than two tons. That might still be barely feasible, but how to charge it within an acceptable time is another question.