What is considered acceptable slip for a boat such as mine? 21 degree deadrise, 2700 lbs, 19' 6" LWL, 5.7 litre 260 hp Mercruiser with 1.47 gear Alpha One drive. I'm turning a once repaired 19" Michigan wheel aluminum 3 blade Vortex. I'm trying to find a GPS to borrow so I will know actual...