Proper Prop Size?

[Darrelweb]

Hi to everyone......I just purchase a 1982 30 foot Catalina. It has been repowered from the Atomic 4 to a Westerbeke 25 HP Diesel. It has 219 hours on the new engine and everything looks and runs fine.

My question concerns the prop. Should it have been changed or sized differently at the time the engine was replaced? When I increase engine rpm above 1400, there does not seem to be any noticable change in speed.

Does anyone have an idea about this or know if the prop should have been size to match the new engine? If the prop should have been changed, what size should it be?

Thanks to all who help. I have gone from a 23' Ericson to the 30' Catalina and the bigger boat is just a dream.
darrel

 

[Dave from Mi.]

Prop pitch and size

Hi;

I have a C30 with a 23hp Universal. I went to several prop sites and sought recommendations. The concensus was to re-pitch my 3 blade 13X10 to a 13X12. Cost was about $100. the boat performs very well, and will go just below hull speed at recommended cruise RPM.

On a side note, I purchased a hand held digtal laser tach, and have been checking tachs on friends boats. Of the 5-6 checked so far, Tachs have been off by 2-450RPM. You might check yours.

Another caution, what ever prop you decide on, make sure you have at least 15% of the diameter of the prop, in clearance between the prop and the bottom of the hull. ie, a 12 inch prop should be no closer than 1.8 inches from the bottom of the boat.

fair winds
Dave

 

[Bob M.]

Yes, you need a different prop

The fact that you are reaching maximum speed at such low RPMs is a likely indicator that you need a different prop. If I am not mistaken,many of the Atomic 4 Catalina 30's were fitted with 12 inch props. I don't know the pitch. But your problem is likely that the pitch of the prop is wrong for the engine/transmission that you now have.

Talk to a propeller specialist, perhaps at an online site. But be aware that such people will often recommend a propeller of a particular size based on theoretical calculations, not experience. You want to talk to someone who has put a prop on a C30 with your engine/transmission combination.

My 1985 C30 with 21 hp Universal M25 came fitted with a 13x12 prop that was fine. I switched it out for a 13 inch adjustable pitch feathering prop, which also was fine. But if you try to go up any higher in diameter, you will have trouble with excessive vibration. The exception is folding props such as the Martec and the Flexofold. I now have the latter prop in a 14 inch diameter (14x11), and it moves the boat very well. It works because the design of the hub is such that the prop, when open, is farther back than a regular prop would be.

If you are interested in a Flexofold folding prop, go to their website and contact their agent, Chuck Angle. He is very knowledgable about Catalina 30's and sold me the right prop that worked.