prop dia

[allymc]

Q. whay difference does prop diameter make??

[onplane]

In general, diameter increases as you lower the pitch.

[allymc]

but say i have a 16" dia prop with a 15" pitch what difference would say a 14" diameter with same pitch make?

[onplane]

By dropping the diameter and keeping the pitch you would be losing overall surface area with less effectiveness. To keep such a low pitch and reducing diameter you may be having engine performance problems, or, are you operating at high altitudes?
The lake I'm at is just under 7000', up here a boat can lose about 30% performance at these altitudes. With these kind of numbers they sell alot of props to people who normally run at lower altitudes. The prop that worked "down the hill" would most likely be too aggressive and the boat never planes. The compromise is to reduce the pitch so that it doesn't "dig" as aggressively and increase the diameter to increase surface area so as to help compinsate with the reduction of pitch. Top end speed will be reduced, alot. The trade off is not bogging the engine and getting on plane. On the flip side, this prop arangement would explode your engine at sea level. Any attempt to go WOT would be like having the rear wheels of a pick up on a oil slick, rev the engine and dump the clutch :shock:
Hope this jabber is of some help,
Scott