fitting double water lubricated shaft bearings

[Bosun Higgs]

My boat has an unusual arrangement for a modern boat - no P bracket but instead a log ( ie a small fin) through which runs a grp stern tube. .

The end of the stern tube sticks out of the log and takes a water lubricated bearing. OK - not to the issue. The boat has a heavy old lump of a Radice folding prop. The GRP stern tube is thick walled so the bearing itself is fairly thin ( 25mm I/D and 1 3/8 OD by 100 mm long) walled. And its all not helped by the final inch or two of the stern tube not being quite circular bore. And the weight of the prop makes the life of this bearing fairly short.

So could I help myself by fitting not one but two water lubed bearings - after all, the stern tube could easily take half a dozen end to end.? Or would I be giving myself difficulties as the engine moves a little on its mounts etc.

 

[Tranona]

No reason why you should not put another bearing on the inboard end, but you must then have a flexible coupling as the shaft will then be rigid rather than floating. Also consider having a composite bearing which you can epoxy into the tube rather than a cutless.

 

[Bosun Higgs]

Wasnt thinking of the inboard end, though in the past I have used Volvo shaft seals which incorporate a water lubed bearing. Instead was thinking of the outboard end ie a 200mm long outboard bearing. Given the distance away from the engine I cant see the extra rigidity being an issue - after all part of the problem with the current set up is the flexibility of the grp stern tube.

What do you mean by a composite bearing? The current bearing has what looks like a tufnel shell rather than a bronze one. Wouldnt dare epoxy it into position though - how on earth would I ever get it out to change it?

 

[Tranona]

Speak to Neil Young of H4 Marine who posts here regularly. He sells solid water lubricated composite bearings machined to size. Glued in with epoxy and removed by heating the tube to release.

If it is really the tube that is flexing then probably better to deal with that by beefing it up.

Wear would be significantly reduced by having a bearing in the other end as the shaft will not move. The Volvo seal still allows some movement on its own.