Best Prop size ?

[<runna10km>]

I have a 20' Skiff with a 115 Enduro and it had a 17 pitch prop on it when I bought it used. It doesn't seem to go as fast as it should. How can I find out how big I can go on the pitch to get the best speed/efficiency ??

[<boats.net>]

We don't have specs. on Enduro Motors, But the USA 2 Stroke 115 operating range is 4500-5500 RPM'S. Prop it to the low end of range for the most speed