2 bladed prop vs 3 bladed

[jimbrown3]

I recently bought a 28 MK II. It came with a 3 bladed prop. I get extreme pull to port when over 1900 rpm. The pull is so much as to be physically tiring. 1) would shifting to 2 bladed reduce problem. 2) will I have to shallow out the pitch to negate effect ?

Anybody else have this problem ?

 

[Calif. Ted]

If it pulls to port while running in forward it's not related to the number of blades on the prop. Does it pull to port under sail ?

 

[jimbrown3]

Yes, only under power. Understanding that there is a pull in ANY single screw; I have owned 10 cruising sailboats and none have acted in this extreme.

 

[Calif. Ted]

Jim, I've run identical boats (270's) with a 2 blade vs 3, and there was no discernible difference in the pull while running in forward.
Seems like this must concern how the propwash is hitting the rudder, the notion that it relates to the distance from prop to rudder strikes me if the helm is balanced under sail, but I'm very unsure. Your description of the problem sounds very familiar but I just can't remember. Memory loss, both a blessing and a curse.

 

[jakez]

I have a 3 blade on my 82 Catalina 30. It pulls to port - harder the more rpms I'm doing. I understand it's pretty much the way it is due to the orientation of the prop with the rudder. I have a wheel - not sure if you're tiller or wheel - so I tighten the tension knob and it helps quite a bit with the pull.

 

[jimbrown3]

Thanks, I really appreciate your reply. I have a wheel and you mirror my experience. I still wonder if a two bladed would exert the same torque ? I wonder if the factory would have an opinion ? I have no idea how to contact customer service. Google has been no help and leads you into dealers. Now that I think of it, maybe that would be a resource.

 

[wufibugs]

Is it possible that he has a slightly misaligned shaft or shaft supports?

 

[jimbrown3]

I just bought the boat used. I guess anything is possible. Am hauling tomorrow to replace cutlass bearing and will get a look see. Thanks for posting.

 

[Donnybrook]

I sailed a C28 MkI with a 2 blade fixed prop and experienced the same thing. Was fine under sail. Pulled much harder to port than my C27 or C30 that I have sailed. On a long trip, I tied a piece of bungee cord to a light line and ran it from the bottom of the wheel to the aft port cleat to neutral out the helm.

 

[anchorclanker]

The number of blades is irrelevant, its something related to water flow over the rudder.

Likely the cutlass bearing is bent or otherwise pushing the prop offset from centerline. As thrust moves off center, the boat yaws opposite, and you have to add in opposite rudder to control it.

 

[jimbrown3]

Thanks. A new cutlass being installed today. Maybe that will help.

 

[anchorclanker]

Check its alignment. A quick and dirty would be to stand back a ways and eye ball down the rudder through the boats centerline and see where the prop is sitting. The rudder and prop hub should both be dead center. The cutlass bearing has nothing to do with how the bracket is mounted to the hull or if it was bent to one side or other.

 

[jimbrown3]

Thanks. It is hauled at the yard. I will check this morning before afternoon launch.