RE: HA3618 in a HYDRO
True.
Have you tried to calculate the RPMs? As I got to know 50 000rpm is more than ok..
4500kv * 14.4 = 64800rpm! in water it will be about 20% less but still quite alot.
so there is a question what prop will "fit", will engine and his bearrings will do and will esc handle the currents?