underdrive pulleys?
 

well I had them on my vette a few years ago and they seemed
to help pick a some extra power , power chip and sidepipes helped too.
But the real question does this give u any gain's in the Boating world???

Underdrive pulleys usually give you single digit hp gains on cars. I have them on my Saleen Mustang and can't tell any difference from when I didn't have them. Idon't think you would notice anything on a boat either. 5-9 hp translates into .2-.5 mph on the speedo, if that.