Mysterious knocking from stern gear

[Spyro]

Shaft knocking on the stern tube will usually be worse when motor sailing on one tack than the other. I had that problem. It also gave a loud knock or two as the engine fired up, hearing it with a slight turn on the rudder would suggest to me shaft hitting the tube.
Disconnecting the gearbox coupling and measuring how much travel there is in each direction i.e. horizontal and vertical travel would tell you if the shaft is centred in the tube. Other than that I would say loose shaft anode

 

[pagoda]

Shaft knocking on the stern tube will usually be worse when motor sailing on one tack than the other. I had that problem. It also gave a loud knock or two as the engine fired up, hearing it with a slight turn on the rudder would suggest to me shaft hitting the tube.
Disconnecting the gearbox coupling and measuring how much travel there is in each direction i.e. horizontal and vertical travel would tell you if the shaft is centred in the tube. Other than that I would say loose shaft anode

An alternative method is to run at the RPM range where the noise is taking place and (carefully!!) push the rubber hose between the stern tube and shaft gland. You may find a push up or down silences the rattle. A slight adjustment of the engine height mounts could be made to achieve the same result. As little as a couple of mm.? Could just be settling of the mounts ?

Graeme