Max Prop Whisper only forward thrust available

[SuzieWong]

Dear Sailing Community,
My boat is equipped with a 5 blade Max Prop Whisper. Coming back into the Marina recently I had only forward thrust (and neutral) available.
When shifting the morse control into reverse the gearbox reacted accordingly and changed spinning directions. Still, the propeller produced forward thrust, although less compared to forward gear.
Tried a few times with high and low revs, always same result. Reduced forward thrust with reverse gear selected.
Any hints what could have caused the problem?
Did anyone with a Max Prop encounter similar problems before?

[donradcliffe]

Have you called PYI?

[Searles]

Have fitted max props for the last 40 yrs, only failure is when the complete prop fell of getting out of the marina ,no split pins in the lock nut ,found prop easy dive easy fix,I for one will be interested in your findings .⛵️⚓️

[SailingHarmonie]

I have had exactly this, although in my case it was reverse only.

The cause was a line wrapped around the prop that prevented the blades from taking their normal position.

I would imagine it could also happen if maintenance was neglected and the prop left ungreased and unable to rotate smoothly on its hub.

Is the prop fouled with growth?

[clownfishsydney]

My guess would be that there is growth on the prop stopping it moving into reverse operation. Had it happen to my Max Prop.

[FabioC]

It happened to me some time ago, although I only had reverse (no forward momentum when in forward). It happened twice, and resolved itself by cycling forward/reverse several times and applying throttle. The Max Prop technician who came to check the prop could not find a conclusive answer, his best guess was growth that prevented the blades to get in the proper position and somehow cleared by itself by cycling forward and reverse. I called PYI at the time, but they were puzzled also.

[SuzieWong]

Thank you for all your replies.
I have dived on the propeller. The boat had been on slip for anti fouling just four weeks ago. Anyway, latest findings do not show any obstruction or growth. All pitch and locking bolts in place. Propeller moved freely from forward to reverse position.
Subsequent engine run was normal. Tried forward and reverse gear several times. At this moment I can only assume that some rubbish (plastic / rope / …) had blocked the propeller blades from moving freely when I tried to dock last time.
Only can hope that this won’t happen too often. This time I had sufficient space for a 180…

[donradcliffe]

On a recent deiivery with a Maxprop, we ran over something at night that caused heavy vibration over 1200 rpm. Tried repeated reverse and forward to no avail, so limped into Newport Beach Harbor and got a mooring. The next morning we pulled a heavy black plastic garbage bag off the prop. Same thing happened coming out of the Suez canal when we caught a woven palstic flour sack, but the water was a lot warmer.

[SailingHarmonie]

Installing a shaft shark or similar cutter is a good idea for a long distance cruiser.

I don’t think a MaxProp is any more likely to entangle trash than a fixed prop, just the symptoms are different when it happens.

[SuzieWong]

Thumping noise

Now, I had been too optimistic too quickly.
We tried reverse on the dock day before leaving, tried reverse on the morning before leaving, tried reverse before entering a bay. Reverse worked flawlessly.
Until we wanted to drop the anchor: loud thumping noise could be heard from the prop . Then the same problem started again: only forward thrust available. Couldn’t dive on boat yet, but I’m worried the internal gear might be damaged