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Overpowered prop?

Oct 10, 2020
5
Catalina 30 Mid Chesapeake
My 1980 Cat 30 still seems to have its original propeller, but the 11 hp engine was replaced with a Perma 30 hp diesel. I'm thinking the engine doesn't like never really working very hard just to spin that anemic prop, and so it carbons up even at 2600. Looking for advice on replacing the propeller. I'm just a Chesapeake Bay day sailor, no racing. The motor is only to get out of and into the bay from my river marina.
 
Apr 5, 2009
1,222
Catalina '88 C30 tr/bs Oak Harbor, WA
The engine supplier should be able to help you with the correct prop pitch.
 
Oct 22, 2014
13,057
CAL 35 Cruiser moored EVERETT WA
I discovered this link to propeller design that is very interesting, by Peter Sewell of NZ.

I have a CampbellSailor designed by WestbyNorth out of Vancouver Island BC. It has been a great improvement on my boat.
 
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Likes: pilott
May 24, 2004
6,504
CC 30 South Florida
A prop is usually sized to the combination of the engine and boat. Your engine dealer should at least be able to provide a starting point on what prop size to use for a 30' sailboat. What is the engine rated limit for RPM? The correct size will be a prop that will allow the engine to reach its top rate RPM with out going over it. Decide between a two or three blade of the same diameter with the corresponding pitch.
 
Oct 10, 2020
5
Catalina 30 Mid Chesapeake
jssailem
What a fascinating story. I'm sure the hull of that boat was very efficient, but the speed of its acceleration in the water, and the lack of huge boiling wake was remarkable.

Unfortunately, my Catalina can handle, I believe, no more than a 12" radius propeller.

Thanks for making me aware of that video.
 
Oct 22, 2014
13,057
CAL 35 Cruiser moored EVERETT WA
I believe, no more than a 12" radius propeller.
What interests me is you might be able to get remarkable thrust out of this prop even in a 12" radius.

If I am understanding the theory, the way that the prop generates thrust is that it is designed to minimize cavitation. Running at a lower RPM and a progressive pitch it optimizes the thrust to move the boat forward.

Looking at my Campbell-Sailor prop, I believe the prop uses similar design traits.
 
Oct 10, 2020
5
Catalina 30 Mid Chesapeake
jssailem

Is what's called a "high aspect ratio" airfoil, like on a sailplane, or the U-2. Less drag, thus turbulence, and more thrust (lift). Can't fit anything like that in 12 inches. But I didn't look specifically at Campbell-Sailor prop. Headed there now. Thanks!
 
Oct 22, 2014
13,057
CAL 35 Cruiser moored EVERETT WA
Thanks. I can understand that. It would appear that the blades are progressively pitched and designed to minimize the cavitation that occurs as the speed differs across the length of the blade.
 

Mikem

.
Dec 20, 2009
717
Hunter 466 Bremerton
jssailem
What a fascinating story. I'm sure the hull of that boat was very efficient, but the speed of its acceleration in the water, and the lack of huge boiling wake was remarkable.

Unfortunately, my Catalina can handle, I believe, no more than a 12" radius propeller.

Thanks for making me aware of that video.
My daughter’s previous Cat 30 had the 11hp universal with a 13” x 9” two blade gori folder. In other words the 13” was no problem.
 
Oct 10, 2020
5
Catalina 30 Mid Chesapeake
jssailem: That Campbell-Sailor prop design looks like a winner to me. I'm trying to collect the information I need to send for a quote. Don't know how long it will be before $1k+ for a prop will become possible.
 
Oct 22, 2014
13,057
CAL 35 Cruiser moored EVERETT WA
Dave. I would suggest that a call to Kelsey at his business office and a discussion with him regarding your boats engine, transmission, design, and purpose for the prop would be valuable to you.

I had a great discussion with him. He helped me select the prop I purchased. Then he engineered the prop to the specifications, and shipped it to me on the schedule he identified. He is a man of his word and I feel a valuable member of the boating community.
 

Ward H

.
Nov 7, 2011
2,715
Catalina 30 Mk II Barnegat, NJ
Just as a another data point, my 93 C30 with 23HP Universal carries a 13RH10 3 Blade prop. Max RPM is 3200, which is to spec.
 
Jul 19, 2013
108
Pearson 31-2 Boston
If you contact a local prop shop they should be able to recommend a pitch change or if a new prop is needed.