My boat currently has a Mercruiser 470 with 1.81 ratio and a Mercruiser 48-78122A4 21p 13 3/4" prop. It's a 21' cuddy and loaded weights about 4000 lbs. Getting on to plane in good conditions can take over 15 seconds, slow. At full throttle my rpm's are at 3800 39mph. WOT range for this...