Quote:
Speed will take care of itself  I am a little at lost on the number thing.
What size prop and what pitch
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It depends on your motor, terry. You want to have the "largest" pitch prop that you can turn and still reach 5200 rpms while fully loaded.
When I was chosing props for Wellcraft's Scarab division, we would load the boat to the maximum recommended load, and then find the prop that gave us the best performance while still able to turn the maximum rpms for that motor. We call that "propping for max of max at max". That's being able to turn
maximum of the
maximum rpm range while loaded at the
maximum weight.
It would be helpful to know the hull weight and maximum load for the hull. I'm going to use the numbers from the old early 70's 21' Regal cuddy to start with. From that I can try to figure you're starting point for propping.
Hull weight (no power): 2175 lbs
Powertrain weight: (383/350, B1 drive) 993 lbs
Fuel weight (100 gallons): 630 lbs
8 persons @ 150 lbs ea.: 1200 lbs
Miscellaneous equipment: 300 lbs
Provisional max gross weight: 5298 lbs
For a starting point, in a Mercury Quicksilver prop, try either the Rev 4 14 5/8"D X 19"P 4-blade, or Mirage Plus 14 3/4"D X 21"P 3-blade, or the Enertia 14"D X 19"P
__________________
Common Sense is learning from your mistakes. Wisdom is learning from the other guy's mistakes.
Fr. Frank says:
Jesus liked fishing, too. He even walked on water to get to the boat!
Currently without a SeaCraft 
(2) Pompano 12' fishing kayaks
'73 Cobia 18' prototype "Casting Skiff", 70hp Mercury