Prop The Question?

[Dave, 397]

I'm hoping that someone here has some wisdom on correct selection of propellors. Yeah, yeah--I know that is a strange question coming from me, but it's like this...

A friend of mine has an older Catalina 30 with a Yanmar, and what looks like it may have been the original prop from the original A-4 installation (not a particularly aggressive pitch). He also has his heart set on getting a 3-blade. The idea of all that drag back there puts my neurotic self in a near apoplectic condition, but it is his boat and that's what he has his heart set on.

I happen to have a 3-blade prop lurking around which was removed from an old Cascade 29 which had been fitted with a 1GM10, and which I would gladly help install on his boat if need be (He's quite capable of course, but I'd do it if it would help clinch the deal) in order to get this thing out of my coat closet!

The 3-blade I have is marked "12 Coolidge 9 RH".
I'm hoping someone on this forum has some expertise with propellor sizing and so forth and can advise...Ryan's scheduled to relaunch on Friday morning, and I would like to send him off with the prop of his dreams, if it is the right one!

Thanks,
Dave

[Tim]

Props need to be fitted to the particular boat and engine combination. Displacement, hull form, prop clearance, engine horsepower, and reduction gear are all factors. What works on one boat may be a total bust on a boat of similar size.

I believe in leaving sizing to the experts. Even they get it wrong often enough. Consult a quality prop shop for the answer. Sorry...I know that's not a great help, but that's what I believe the answer is.

FWIW, the prop on my boat is a 12x13 3 blade. 12x9 is awfully flat, pitch-wise-. Any prop on any boat should be able to allow the engine to turn at its rated WOT. There are lots of incorrect props on boats, and they all work, to an extent. Any prop used with an A4 is not ideally sized for a modern diesel; the power curves are too different.