Prop selection 20SF

[rcnight]

Thought I’d take advantage of some nice weather and try out some props hanging around the garage. This is for my 20SF pushed by a Suzuki DF140. My go to is a Suzuki SS 3x14x20. Can’t complain. I have an aluminum Michigan Wheel 3x14x19 and a Power Tech SS 4x13.5x21. Have to admit, I got lazy and never changed them out. Am I missing anything?

[Fr. Frank]

Originally Posted by rcnight

Am I missing anything?

Yes. You're missing the test data from the other two props.

You want to look at a few things when you compare props: diameter, pitch, cup, blade width, rake, and rake curve or progression. Some props also use a progressive pitch ratio. They all make a difference.

One note: SeaCraft hulls ALL really like stern-lifting props. This is due in part to the VDH design which gives no flat perpendicular planing surface to provide that lift. More pitch close to the hub gives greater stern-lift. This is why a 4-blade prop of a given diameter and pitch has much greater stern-lift than a 3-blade. It moves a theoretically similar column of water the same distance, but the additional blade, area near the hub particularly, gives it more lift.

But just like flaps on a plane, the added lift also gives you 1/3 more functional drag at the blades.