Yanmar SD60 or Flexfold prop?

[woc]

One of my saildrives (Yanmar SD60)with 3000 hours started to “ disengage” when engine RPMs exceeded 2000. It would reset itself after returning to neutral.
Yanmar inspected it and could not find a smoking gun to identify the problem.
Both saildrives have since been replaced with new units. To my surprise, the same side drive is now doing the same thing I.e. “ disengaging” at the same rpm.
I have Flexofold 3 blade props. I might point out that the engines had new clutch plates fitted. Also, the gear lever on the saildrive stays engaged when the saildrive looses thrust and engine rpms go up.
Has anyone had a similar problem and if so what was the cause?
I am beginning to suspect a problem with the props. I never heard of a folding prop closing whilst spinning but that is what it feels like.
My plan is to swap the props from port to stbd to remove the guesswork.
Any thoughts?

[DougR]

I might suspect that the rubber cushion hub in the FlexOFold prop has spun, and when you obtain a certain RPM/ torque the rubber begins to slip inside the bronze hub. Bringing the RPM back to to idle and neutral allows the rubber to grab again until you reach that torque next time.

Swapping props port to starboard should point out whether the problem follows the prop or stays in the saildrive.

[a64pilot]

Why did you replace the saildrives?

[woc]

Originally Posted by DougR

I might suspect that the rubber cushion hub in the FlexOFold prop has spun, and when you obtain a certain RPM/ torque the rubber begins to slip inside the bronze hub. Bringing the RPM back to to idle and neutral allows the rubber to grab again until you reach that torque next time.

Swapping props port to starboard should point out whether the problem follows the prop or stays in the saildrive.

Thanks for the reply. Agree with your comment but thought once the rubber cushion slipped it would not be able to grab again. Will know for sure after I swap later today.

[woc]

Originally Posted by a64pilot

Why did you replace the saildrives?

Galvanic corrosion on the lower legs caused by stray current in a marine that went undetected for three month. After eating up the anodes it ruined the housings. I have since installed a galvanic isolator that will hopefully prevent this in future and will check the anodes more frequently.