cutless bearing llubrication

[azuredragon]

We've had our 50 year old steel Adams 45 for seven years. At our latest haulout we discovered the cutless bearing needed replacing and we hired a marine engineering firm to do the job. Unfortunately I am not able to be present during the time of the job.


This boat has a long shaft, roughly 3m. The stern tube runs from the engine room bulkhead to the end of the skeg and is entirely within the hull and skeg. There is a dripless seal on the engine side of the bulkhead.


I spoke by phone with one of the engineers and learned the following. The cutless bearing was worn right down and had no ridges left. This apparently allowed the shaft to wobble so bad that it wore on the stern tube. The root cause analysis of this situation concludes that the installation made no provision for water to flow through the stern tube and lubricate the cutless bearing. Given the age of the boat I suspect that the stern tube may have had a water feed from engine cooling at one time but at a later time the engine was converted to keel cooling with dry exhaust so there is no water source in the engine compartment to feed the stern tube.


The engineer recommends to install a fitting on the stern tube near the end that goes through the engine room bulkhead and fit an air vent (tube or hose) to this fitting and lead the tube up high in the aft cabin to ensure is always above sea level even when heeled.


I am told that this will allow sea water to enter the stern tube through the cutless bearing but without this "vent" air pressure would likely inhibit such flow and result in rapid cutless bearing wear.


Having known next to nothing about stern tubes and cutless bearings before now the above explanations seem logical but I would appreciate any comments more experienced members would like to offer.

[Ballsnall]

I'd have to call BS on that advice. Regardless if there was a vent or not the water will still enter the cutlass bearing. Water injection should not be necessary on a low speed shaft. Possiblity of sinking the boat if the vent ever fails. A simpler solution is just to bleed the air from the stern tube at the dripless seal which should be fitted with a water injection point/bleed anyway.
How old is the cutlass bearing? Maybe it just wore out due to normal wear.

[fourlyons]

I agree with the previous poster, air entrapment in the shaft tube can cause the gland packing or dripless packing to overheat, but seems unlikely to affect water flow down at the Cutless bearing.
Most full keel sailboats I see around me don't have any forced water flow to the Cutless bearing and do fine. My understanding is that the vent / water line to dripless packings are to vent air out more than anything and keep them from overheating, otherwise you have to burp them occasionally.

That is however a very long shaft. Does it have any intermediate bearing support. Perhaps shaft whip is causing wear in the Cutless bearing? If not, is the shaft diameter correct for that sort of length?

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