2 blade, 3 blade, etc.

[jim]

I'm considering whether I should upgrade the prop on my boat (an O'day 31 w/18 hp universal engine). It currently has a small 2 blade propeller and thought I'd see what people thought about 3 blade propellers and whether there's any real advantages to making a change.Thanks.

 

[GailForce]

Props

I guess if you've though about changing props you must not be happy with the one on the boat now. Unless your not achieving hull speed with your current prop I wouldn't change it. The exception might be a folding or feathering type but those get pretty expensive. If your not getting to hull speed a discussion with a prop guy might help diagnois potential issues. Cruising RPM's, prop diameters and different pitchs. Check with people in your harbor for local prop service they have been happy with.Jeff

 

[Marshall]

Changing Props

At the Annapolis show a couple of years ago I had the opportunity to ask the Westerbeke/Universal people about changing props for a 12 HP Westerbeke and was told that I wouldn't gain anything by changing for that particular engine and boat. You may want to contact the engine maufacturer and ask.

 

[John Tesoriero]

It depends!

If you have the absolutely correct propeller diameter and pitch for your boat and engine combination, if you can reach hull speed at approx. 85% of max RPM, if you can reach near max RPM (for your engine) in gear, if your engine does not overheat or smoke at 85% of max RPM, if you don't loose much speed when powering into a head wind and if you don't have a bothersome vibration with everything else aligned, THEN you probably would not benefit from switching to a three blade. Others will chime in with comments about increased drag, etc. but I would recommend adding another blade after talking to a few prop manufacturers about the correct set-up for your application.

 

[Ed]

prop change

I changed my stock bronze prop on my old 280 (Westerbeke 12 hp) to a crusing design (sailCDI.com)2 blade perfect pitch prop and was amazed by the added thrust when backing up. The boat also seemed to reach hull speed with about 400 less rpms than with the old prop.I just ordered one for my new 322, and no I don't work for CDI. One of the principals, Joe Daymon, was hired by O'day corp to work with CR Hunt to redesign props for the O'days.

 

[Kevin]

I agree with John

I switched from a fixed 2 blade to a 3 blade to address some of the problems that John mentions. I'd recommend getting feedback from other owners of your model boat on what worked for them since prop selection seems to be half science and half art. And keep in mind any changes the builder may have made to your model over its production run. For example, my boat was from the first year of production and the strut for the cutless bearing/shaft was about 1.5 inches shorter than later models which meant there was only 1" of clearance between the tip of the prop and the hull. A smaller 3 blade worked for me but might not be necessary for the later model boats.And since John brought up drag. I can't tell the difference.....when the wind is just right I still hit hull speed. Kevin