Newage PRM 160 gearbox - prop moving freely on sailing

[Briis]

I have a Newage PRM 160 (VR2 model) gearbox, while it seems to work OK with the engine the the prop is singing like mad when I sail without the engine. It's kind of annoying, especially when surfing over waves the pitch goes up and down. I wonder if it's normal or any detail is worn out, i.e. any of the two clutches?

Or should the prop move freely with that gearbox model?

[DougR]

Yes, the prop can freewheel when sailing. According to the PRM 160 manual the gearbox can be freewheeled or trailed for an unlimited time without damage to the box, so I wouldn’t worry too much about that. What you might be hearing is normal gear mesh whine that occurs all the time but is hidden when the engine is running. A folding or feathering prop can solve this, or a prop shaft brake.

On the other hand you allude to the prop “singing”. Is the noise coming from the prop or the gearbox? There is a phenomenon known as prop singing which is a vibration/whine coming from the trailing edge of a propeller blade that is caused by poorly shaped blade trailing edges. I have experienced this with some props when under power, but have never heard of it when the prop is freewheeling when sailing. Perhaps others have experienced it when freewheeling.....? Slight reshaping of the trailing edge of the blades can usually resolve the issue under power.

[Briis]

Thanks Doug. I guess it can potentially be the worn cutlass bearing that makes that whineing noise as well since I took the gearbox off and the output shaft bearing look smooth and noiseless when turning.