3 Blade Performance
Q: I am in the process of buying a Catalina 34 Mk II. I have seen the discussion on going to the three bladed prop vs. the standard two blade prop. My question is do I still look toward getting a 15 X 10 pitch prop even though the newer Catalina's have a 30 hp vs. I believe the older 25 hp diesel? Will the increase in horse power make going to a 15 X 9 pitch prop more likely? Do any of the newer Catalina 34 MK II owners have the three bladed option?
I have a 1988 Catalina 34 with the MXP25 engine. In 1992 I had my prop repitched from a 15 x 9 to 15 x 10. At 2500 RPM on the engine my over water speed on a calm day went from 5.0 knots to 6.1 knots. It will depend what the output in RPM's the shaft is turning as to what speed you will get. If you can find out what the shaft RPM's are for a given engine RPM between each engine, then you should be able to make as wise decision as to either the 15 x 10 or 15 x 9 prop pitch
I have a late mkII with the 30 hp engine and the standard 2-blade prop. I believe my prop is 15x10. There's plenty of power with the 30hp. I don't see any need to go to a 3-blade prop unless its a feathering prop and then only for added smoothness under power and reduced drag under sail. I don't think the benefits of a 3-blade fixed prop are worth the drag
Don't let the boatyard talk you into getting a "powerboat" prop - you need a "sailor" prop, which has considerably less mass. If you get a 3-bladed prop that isn't a "sailor" prop, your engine will smoke!
The 15 X 10 is the right pitch for the XP 25 The factory used a 15 X 9 based on some unknown factor , most of us have up grade the pitch to 10 , I did it the first year of ownership, 1988. You will like it better.
Dave, NONSENSE #713
Just had my 15X9 repitched to 15x10 based on numerous recommendations to address my slow speed problem. Haven't been launched for the season yet, but am looking forward to seeing the results. I'll let you know. by the way, with the 15x9, temp stayed at 165 degrees at 3000 rpm's, so that helped convince me that an extra inch of pitch wouldn't be detrimental to the engine.
Ed, Tail Wind #866
Had my 15X9 repitched to 15X10 by black dog propellers in Maryland. Now cruise at 6.1-6.3 Knts GPS instead of low to mid 5s. This is with a M25XP running at 2800 RPM with a max of 3400 RPM. The RPM is uncalibrated but my cruising RPM is around 80% power. I highly recommend this upgrade in pitch.
Bill Humphrey "Grace Under Pressure" #1026