For that size model
I use a Hobbyking 3639-1100kv brushless motor
or a D3548/4 1100kv on a 3S lipo battery
(between 3700-5800mah), a 60 or 100Amp car ESC (HK-60A-SL or HK-100A), program card(HK PROG-CARD).
I have a good setup for this system
, if you require.
Prop start with the one you have, but I use a 2 blade 40mm or 3 Blade 37mm (brass or CNC).
Slightly over scale speed, depending on the boat.