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cyphert · 29-03-2016, 05:28

Any advice on the following situation? I have a 2-blade flex-o-fold propeller on a Yanmar SD20. I'm getting some kind of vibration, actually sounded like a slapping on the hull, when I power up past 1700 rpm but only in forward gear. No problem in neutral or reverse at any rpm. I thought I might have a rope snagged on the shaft but when I dove and inspected the prop I noticed nothing visually amiss. Blades looked undamaged, nothing seemed any different from the flex-o-fold on the other saildrive (catamaran). My mechanic says that he does not believe the sound is coming from the engine nor the saildrive. I'm stumped?

MARINE ENGINNER · 29-03-2016, 07:51

did you check your engine mounts?

M.E

ausnp84 · 29-03-2016, 08:15

Weird. Have you got an underwater camera that will allow you to have a good luck at the FoF spinning?

We run two on our current motorsailer and haven't had any vibration issues.....

n

cyphert · 30-03-2016, 05:27

I had a marine mechanic look at the engine and saildrive. He didn't think the vibration was in either. I assumed he checked the engine mounts and saildrive mount but I'll double check today. He suggested I switch propellers (catamaran) and see if the vibration follows the propeller. Sounded like a good idea but the water here has about 4 inch visibility so I was hoping that someone had similar experience and could give me an "easier" fix.

EWOL Props · 30-03-2016, 08:30

For prop switching you should first be sure that they are rotating in the same direction (not counter-rotating), otherwise you will go backwards instead of forward.

Typically the vibration after a certain rpm only is due to resonance and/or different pitch of the 2 blades, for example if one blade is slightly warped you may not see with naked eye but the pitch of one blade would be different to the 2nd blade. Then the rotation at a certain speed will cause vibration (different to vibration due to unbalancing that happens at any speed). Please check also that the stopping point of each blade is not damaged, deformed or missing of stopping rubber inserts