If the pitch is 1.58 inches (40.132 mm) Then your top speed should be 28mph. If the pitch is 25mm, then top speed would be 17mph. Loaded engine RPM would be 24,797.

These figures take a motor efficiency of 82% (Brushless motors usually have efficiency ratings between 80-86%), and also a prop slippage factor of 25% (Typical of a mono hull).

Go up 1 cell to 8.4v and the numbers go to: 32mph & 20mph respectively. 3 Cell lipo (11.1v) = 43 & 27.

32mph in a boat that small is probably not controllable (AKA nearly flying!). Let us know how it turns out!