3 Blade Propellers

[Jim Miller]

Anyone have any experience with 3 blade propellers? How do they compare with 2 blades for thrust, speed, vibration, etc? I am particularly interested in application on a 33.5 with the 18 hp Yanmar.

 

[Jim Ewing]

Assuming you mean...

...fixed blade props. When we got our 37.5 it had a two blade we changed it to a three blade after motoring and motor/sailing down the ditch from Charleston to Jacksonville. With the three blade we went from JAX to West Palm Beach. Based on that experience and some local ocean motoring I'd offer the following.The three blade is MUCH smoother. The three blade is easier to maneuver with around the docks, the prop walk is a bit less and you have more thrust sooner. Backing is easier. Speed is the same but the three blade seems to handle powering into chop and wakes a bit easier. More drag with the three blade under sail, but only really noticable in medium wind speed (10-12kts). Slower than that and the boats only going 4kts anyway, faster than that and you're approaching hull speed. I'd like to get a 3 blade Autoprop but haven't been able to rationalize spending that much money for 1/2 kt.Jim"Prospect"

 

[Chuck Wolfe]

37.5 and Autoprop

First I had a two blade. The "two" stood for "too much vibration". Switched to a 3 bladed immediately and used it for about 14 months. Vibration virtually disappeared. Got an Auto-Prop. I can only say "wow". I used to do 6.7-6.8 knots @2750 RPM. I now do 7.4-7.5 knots at 2500 RPM and my throttle throw is only about 1/2 way so my fuel consumption is way down. My engine temp remains the same. I sail in light winds much faster and the other day I was coming down wind in 7 knots of wind doing about 3.1 or 3.2 knots. I turned the engine on and at 1100 RPM I was doing over 6 knots and it was quiet as can be. There are several virtues to this prop, some of them unexplored. The backing is great etc.Chuckwolfe@mail.com