RE: speed controler
At only 23amps continuous it possibly wont be able to handle the 2 motors at full throttle in a boat,it is more for a car where it wont be running flat out most of the time.
You could buy two and wire each motor to each esc,but would be more money.The 90 amp one would be a much safer bet,motors wired together.
Which boat is it? submerged prop,surface drive?
Brod..