Vibration and noise after changing propeller

[BOBBIN]

Recently fitted a Darglow featherstream, replacing a fixed three bladed propeller. All works smoothly, forwards,reverse and feathering.
However, at about two thirds revs, I am getting vibration and noise which appears to come from the shaft log. Nothing has changed, cutlass bearing is not worn, PSS shaftseal doesn't drip, engine mounts and R&D are tight.
Anyone have any ideas what could be causing this and how to fix?

 

[Heckler]

Recently fitted a Darglow featherstream, replacing a fixed three bladed propeller. All works smoothly, forwards,reverse and feathering.
However, at about two thirds revs, I am getting vibration and noise which appears to come from the shaft log. Nothing has changed, cutlass bearing is not worn, PSS shaftseal doesn't drip, engine mounts and R&D are tight.
Anyone have any ideas what could be causing this and how to fix?

Harmonics! Best of luck with it. Fine tuning as they say in their blurb!

 

[Dull Spark]

A PSS seal, unlike a packed gland, will provide no support to the shaft, so it is supported on the R&D coupling and the P bracket only. There is not much to adjust before you have to consider mods to the propeller, but it may be worth moving the shaft anode (assuming you have one) as close to the P bracket as possible. (Leave some clearance for shaft axial movement and flow of water. Say a couple of finger widths.)

If it were mine, I'd be checking the shaft line-out as though I'd just fitted a new engine. Take the coupling apart and check for misalignment etc. Most engine installation manuals give the details. Check the shaft is central within the shaft log.
Good luck!

 

[vyv_cox]

Harmonics! Best of luck with it. Fine tuning as they say in their blurb!

Exactly. Adding a relatively heavy propeller to a long slender shaft changes its natural frequency downwards. For us with a Bruntons the critical speed is 2000 engine revs, when resonance occurs, shaft lateral displacement increases and several locker doors in the galley rattle.

 

[BOBBIN]

No P bracket just straight shaft log with cutlass bearing at one end and PSS seal at the other so no anode. The shaft seems central.
You can see why I am baffled. Thanks

 

[Dull Spark]

I'd still check the shaft line to rule out misalignment. Whatever it's critical speed, things don't improve if the coupling is misaligned.

Has the Darglow got a significant overhang on the end of the shaft? That would reduce critical speed.

If the Darglow blades at their closest point go too close to the hull or rudder, it can cause "pulsing". May be worth checking.

Also, final thought: are all the blades set at the same angle? I had bad vibration on mine after the rope cutter spread debris on the propeller and one if the blades refused to take up the right angle. All was back to normal when I removed the stuff and got all three blades moving across their full range of travel.