Right prop for Catalina 30

[zighamner]

Hi everyone,
We just purchased a 1982 Catalina 30 tall-rig and love sailing it. However, the previous owners replaced the Atomic 4 gas engine with a diesel Volvo Penta MD2010 that only generates 10 horsepower. They did not replace the propeller which is a 12" 7 pitch fixed 3-blade. The throttle has got to be really increased to get out of the slip in reverse and even in forward it seems the engine's RPMs are very high to get any kind of speed. I think that with the diesel we can handle a larger prop (maybe a 13") and a bigger pitch (maybe 8 or 9). Anybody out there with comments or suggestions???

 

[jrowan]

I'm sure there are as many opinions on this subject as there are different props out there for sale. The C 30 always has put up a lot of initial resistence when reversing out of a slip. Because she is a beamy boat & because the prop os so far from the rudder due to mid engine placement, she takes a boat length or more to respond to the helm. That's why I have to gun the engine a lil to get her to turn at all, in the marina. You may also get a diver to check your bottom & prop for barnacle or sludge growth as this can affect prop efficiency tremendously. With our small 5411 diesel, I get our prop cleaned monthly by a diver in the sailing season. Otherwise a stiff chop at the dock can pin me to the pilings!

Prop sizing is as much a science now - I would contact your local Volvo-Penta dealer for their advice, since its their engine. 10 horses is very marginal power, & you will generally be throttling your engine at least 2/3 throttle to get any speed at all. Later model C 30's have 23 HP Universal diesels that were more then twice our HP. My 5411 can achieve about 5.5 knots in calm water. Most of the older, big Atomic 4 motors could not do much better, because of their 1:1 gear ratio didn't allow the engine to rev up enough, via use of gear reduction like modern 2:1 ratio.

A 3 blade prop that you currently have should provide more torque then the standard 2 blade, but sacrifices speed under sail due to increased drag. You will likely not be able to install a larger prop due to the close tolerance of the prop edge to the hull is already tight on the C 30. Also a bigger prop will tend to over-torque against your already overworked engine. Pushing it too hard risks wearing out the bearings, trans & engine prematurely. A good sign of over-torqueing & loading of your engine is seeing black smoke out the exhaust, then back off the throttle.
I kept my 2 blade prop for better sailing speed, but I'm on the Chesapeake with lighter winds & tidal currents then you may experience.
Next time you haul out have an experienced Volvo diesel mechanic evaluate your current prop & engine set up combo. But a new prop is an expensive investment, so you want to get it right the first time.

 

[Stu Jackson]

jr's advice is good.

What you really need to do is find out what the reduction gear, if any, is from your engine to your prop through the transmission. You didn't say.

Find out what you have, then talk to a prop shop.

Good luck. Recognize this: You have a pretty unique C30 arrangement.

 

[zighamner]

Thank you. Very, very helpful and informative. I appreciate this very much!