Flexofold sizing

[Olivia Mae]

Question on Flexofold 3 blade prop sizing for those who have one. I've read the existing forum posts on this board and am more confused than ever after getting a quote from flexofold.

Our 2003 has a 3 blade fixed Sailer on it (14 × 10) that works fine. M35b engine with ZF15 MA transmission with 1.88 forward 1.95 reverse gear reduction.

Flexofold initially recommended a 15 x 10, 3 blade per specs they noted was 1.95 : 1 gear reduction. I brought the mistake up to them and had to send them a picture of the transmission nameplate to convince them it was 1.88 : 1. Now they are recommending a 3 blade 17 x 10 prop.

From what I've read here on previous posts, the 15 x 10 would be slightly overpropped for this boat, and I'm assuming the 17 x 10 would be seriously overpropped.

Thoughts?

[yodagwb]

The transmission gearing is what is driving the difference. Your prop is turning slower than the 1.95:1 gear ratio so to adjust the pitch and size is increased. During the 350 run Catalina evidently used a couple of different engines and different transmissions. Flexafold seemed to have it down pretty good. I know in my case the 15/10 was considered slightly on the over pitched side but everything worked out fine. I just keep an eye on the temp when pushing the RPM, over the top recommended cruising RPMs, as it will starts to rise, but a little better speed at the lower RPMs. I would do the exact same thing over again.

[Olivia Mae]

Yeah, I get that. I never did measure, but I have my doubts there's enough room for a 17" prop, especially with the documented cavitation issues on these boats. I see the 15 / 10 most often mentioned on this forum as being the best size flexofold, but slightly over propped. That would also make the 17 / 10 more than slightly over propped, BTW. I'm assuming you also have the 1.88 forward gear ratio on your 350?

[yodagwb]

I believe I have the 1.95:1 hence the 15/10 prop size.

[philliphyatt]

15:10:3R Here 2007