Doby runs a 1860kv 1521 1.5D, 51mm prop, 4S2P.

If you go to 6S with a T180 this motor runs very nicely: MOTOR and you can start with a Octura X442 -M445 or Carbon 42mm -45mm 1.4pitch props.

What cells exactly do you have as it makes a pretty big difference. The higher the C rating the better for boats because boats are the hardest on electronics of any RC model type.

Amp draw: Bigger prop more amps no matter what voltage you run. Smaller prop more run time, larger prop more speed and amps but, shorter run time. Setup is important also to avoid excess amp draw. Pond time, test for 1 minute, check, test again, check, repeat, repeat...