Prop selection for a 20sf w/ 130 Yamaha --Help--

[BoniB]

I'd like to install a SS prop, what size and pitch would be best for my 1974 20sf with a 130 Yamaha?

Thanks,
John

[workinpr0gress]

17 pitch should be good n a three blade

[BoniB]

What would the diameter be? 13"??

[McGillicuddy]

Yeah, 13" diameter. 13x17 should be about right in 3 blade. The semi-cleaver geometry from Yamaha is probably a nice match. You can might try to borrow a decent one from a prop shop to see how it feels. If not find them like new on ebay for $50-80 in Al.

PT Props has nice SS called SCD3 and a 4 blade called SCD4. A four blade of that geometry would probably get you max efficiency and about 38 mph. You might need drop to a 15 or 16 pitch in the 4 blade. Good luck. Post some results.

[Bushwacker]

Are you currently running an aluminum prop? Best to get it dialed in first (so it turns max allowable rpm at max load) with the aluminum prop, since aluminum props can be repitched easily to adjust max rpm. Once you know that, it's pretty easy to find the equivalent SS prop, which will have slightly more diameter, pitch, or cup.

That's a pretty light motor, so you may not need a stern lifting prop, but I've found that the 4 blade props give great low end acceleration and mid-range mpg, although they may cost a few mph on top end. They'll also help you plane at 10-12 mph in rough conditions which is big deal if you run in rough conditions.

[BoniB]

I have an aluminum prop on now; it seems to turn the right rpm but I'd like to switch to SS. Would I notice a difference in performance between aluminum and SS?

I'll pull it off this weekend and check the size. Usually I cruise at 4000 rpm @ about 23kts, half tank of fuel one adult. I'll record a full range of rpm and speed this weekend and post.

What would the fuel consumption (gph) be with the 130 Yamaha on the 20sf at say 4000 rpm?

John

[Bushwacker]

. . Would I notice a difference in performance between aluminum and SS?

I've typically seen about a 3 mph speed increase and maybe 0.5 mpg improvement switching from aluminum to equivalent SS prop on my E-Tec. Have no experience with Yahamas.