Speed test today proved satisfactory.

[ParallaxBill]

I got my 18' 73 Glassmaster tri-hull w/165 L6 Mercruiser up to 41 mph (gps) today on a windy choppy lake. Top indicated rpms were 4,300 with a new Mich Wheel aluminum prop (14.5"X19" pitch). Two adults on board with 2/3rd's fuel load.

Seems like I've found the right combination.