Re: lower pitch prop and speed reduction
How much speed you get from a prop is a function of how well suited it is for your boat/motor setup. There is no guarantee that you will lose any speed. In fact you may even gain some speed.
On my current setup I have 3 props; 2 of them are 17p and 1 is 15p. All of them get the same top speed within 2mph of each other. The 15p is the fastest and also gets me closest to the top of the recommended RPM range for my engine.