First off, what voltage? Regardless, the Kv is too high for a fully submerged prop if you want any run time. You will want a prop about 1.5" in diameter with no more than 2" of pitch. Less would be better. On 2S a Kv of 700-800 would be plenty, otherwise you will draw way too many amps and overheat the motor and ESC. On 4S, 300-400 Kv should be close, too much and you will overheat. Run time will still be limited wit the size of cells you could fit in that tiny hull.
It takes a huge amount of power to move a fully submerged sub rapidly, particularly if it is not well streamlined with a tapered tail. Five mph is almost 8 feet per second and would be tough to achieve on a small boat like the one you propose. What speed do you want?
Last edited by Got RPM; 10-12-2013 at 07:25 PM.