Hi all. Just bought a 1984 Catalina 27 with a 15HP Universal Diesel. It needs a new propeller. What is the best way to determine best pitch for a new 3 blade propeller? I know that it fits on a 1" shaft. Thanks.
Propeller pitch
- Thread starter randyprint
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Many variables to consider when sizing a prop. Often, the factory prop is not sized properly. First thing to consider is what engine you have. If original engine is installed, it could be a Universal 5411, raw water cooled, 11 HP or the Universal M-18, fresh water cooled, 14 HP. You need to know the distance between the prop tip and the hull. Should be between 1/6 to 1/7 the diameter of the prop. Assuming that you have the M-18 engine and original prop strut, a very ball park estimate would be you need a Michigan Wheel 3 blade, 13X10 RH (right hand rotation) prop. So what happened to the old prop?
You may want to consider using a 2 blade prop. A little cheaper and you won't loose as much speed when sailing. 3 blades create quite a bit more drag than a 2 blade.
Be careful King Air - I always advocate the two blade prop to other Catalina sailors & then get my head bit off from folks that seem to want more torque under power, then speed under sail. I still have the old fashioned notion that we sail yachts, not power boats. Funny how every publication that I've ever read from Practical Sailor, Sail Magazine, Nigel Calder & Don Casey agrees with us, but we still seemed to be in the minority here when I say that whatever torque gained under power with a 2 blad prop, is not worth the loss of speed under sail from the substantial increased drag. Wait & see the arguements that start from here
I guess the correlation between airplane props and boats props goes just about as far as the math and physics...
Funny, when the military and civilian aircraft designers did all their studies prior to WWII that proved the most efficient propeller for an airplane was a single blade with a counterweight. And yet, you NEVER see any single blade props!
Yes, the 3 blade will provide more static and low speed thrust, the 2 blade will provide more high speed thrust.
We have 2 identical Beech King Air 90's. One has 3 blade props and the other 4 blade props.
The 4 blade takes off and and climbs better, the 3 blade cruises faster.
*shrug*
So the thrust argument is valid. If someone is willing to trade off on drag.
Me personally, if I could afford it, would have a feathering, 3 blade prop.
Funny, when the military and civilian aircraft designers did all their studies prior to WWII that proved the most efficient propeller for an airplane was a single blade with a counterweight. And yet, you NEVER see any single blade props!
Yes, the 3 blade will provide more static and low speed thrust, the 2 blade will provide more high speed thrust.
We have 2 identical Beech King Air 90's. One has 3 blade props and the other 4 blade props.
The 4 blade takes off and and climbs better, the 3 blade cruises faster.
*shrug*
So the thrust argument is valid. If someone is willing to trade off on drag.
Me personally, if I could afford it, would have a feathering, 3 blade prop.
Catalina 27 prop request
Thanks Donnybrook! My old prop's blades are deteriorating on the edges due to previous owner not replacing a zinc in time. I just had my diver go down to read the numbers on the existing prop. He says it is a 15" and either a 24 or 34 pitch. Yes, I have the Universal 18 diesel. I'm assuming that it would be a 24 pitch.
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