Unexplained Cutless Bearing Wear

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sailor22

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My boat has be out of commission, afloat in Portsmouth Harbour for 16 months. In that time the engine has been run and the shaft turned for 30 minute periods to ensure that any fouling on the shaft in way of the cutlas bearing could not build up.

The last time that the boat was underway with the engine was in March this year, after the winter lay-up afloat, and 10 months since launch with a new cutless bearing. The voyage was about 20 minutes and included a brief period at full power to "blow the dust away". It was cut short because of a loud banging noise coming from the propeller area (loose anode?, loose rope cutter?, losse Cutless bearing or housing?, loose propeller?, debris strike?). We made it to our buoy, just!

The noise was very apparent going ahead, but not going astern, initially. Then it became inevitable, both ahead and astern.

Subsequent attempts at inspection using under water cameras etc were unsucesssful. for various reasons. Divers and a tow for a brief lift out and inspection, could not be arranged satisfactorily.

The boat was not used but the shaft was turned momentarily every few weeks.

Lift out today revealed nothing apparently wrong. Everything appeared to be secure and in good condition once all the marine growth had been blasted away.

Rotation of the propeller revealed a slight knocking noise from the propeller shaft log tube in the hull, just forward of the Cutless bearing housing. However, closer examination showed heavy wear to the Cutless bearing. Shaft movement athwartships was about 0.5mm while in a vertical direction, it was about 3 to 4mm.

That is quite some wear for 16 months and a total of about 3 hours motoring!

Any ideas anyone? How do I stop it happening again?
 
Are you absolutely certain that the cutless bearing was new? I find it inconceivable that such wear could occur according to your description. The only possible scenario I can dream up is that the water flutes in the rubber were blocked by fouling so that the bearing ran totally dry. Seems unlikely.
 
A couple of things spring to mind. I had a wear problem on my boat, not nearly as bad as yours but bad enough to require replacement every two or three years. it was an engine mounting problem initially, but compounded by a prop shaft that was out of true. if your boat has a "P" bracket and a length of exposed shaft, it's quite possible that a slight bend in the shaft would do this. it's only have to be a few thousandths out for the wear to start. An out of balance prop might have a similar effect.
 
What Topcat writes is certainly a possibility. Certainly the only wear of that rapidity I've encountered was due to a bent shaft, which appeared to have been caused by the prop picking up a rope or net under previous ownership with sufficient force to throw the engine alignment out horizontally. Perhaps the OP would know whether such an event was possible?
 
We used to have considerable problems with calcium deposits within our cutless bearing which caused horrible branching noises and fairly rapid wear. My engine guru fitted a polyurethane lined bearing which seems to be much longer lived and curiously seems to be less attractive to the marine life which creates these deposits.
 
Thank you everyone for your contributions.

Yes, when run during the laid -up period afloat, the boat was in gear, turning the shaft with its fixed-bladed prop to avoid any build-up of marine growth deposits on the shaft in way of the cutlass bearing and attendant damage to the bearing.

The bearing had been changed due to previous wear from this cause.

It is a new shaft, carefully aligned when last ashore.

There has been no significant opportunity to pick up debris to be sucked into the bearing. Had anything come near, my Ambassador Cutter should have seen it off. There is no evidence of the cutter operating.

The Cutless bearing is mounted in a Volvo Penta Housing screwed to the shaft log tube and bolted to an extension to the back of the keel., ie not in a P-bracket.

Nevertheless, I remain mystified by the excessive wear and its cause.
 
Managed just 3 years from our Cutlass moored near Premier in Gosport. Orginally put it down to visiting Ashlett Creek and drying out in the mud, actually ploughing it to get to the jetty. Same with a visit to the Royal Victoria IOW. However, it may well have been a build up of fouling in the cutlass bearing.
Anyway replaced it with a more expensive bearing from:

http://www.countrose.com/content/lining_material.asp

So far so good but it has only been a few months. However, these folk mould the bearing then machine the final inside diameter. The cutlass bearings from the chandlers have moulding marks on the inside. Does this make a difference? possibly when combined with the polyurethane material.



Pete
 
Cutless bearing replacement became an annual event for us although everything appeared to be OK alignment wise. Went through it all thoroughly last winter, even had the shaft, couplings and prop checked for true in a local engineering shop. After assembly checked shaft again with dial gauge.

In the end it appears that the Vetus bearings from ASAP supplies were oversize internally so another make supplied (can't remember the make) which is a much snugger fit. The Countrose bearings mentioned by Pete7 have good reports on the MOA forum.

I'll have to wait a while to see how the new bearing lasts as the boat hasn't moved off the mooring this year due to other commitments.
 
How long has your shaft seal lasted - a badly aligned shaft/engine can shorten the life. My last Volvo seal lasted 20 years and was only changed for safety. A short life here could point to your problem......
 
Chris_Robb said:
How long has your shaft seal lasted - a badly aligned shaft/engine can shorten the life. My last Volvo seal lasted 20 years and was only changed for safety. A short life here could point to your problem......
Click to expand...

Certainly my shaft is aligned <5 thou around 360 degrees at the couplings and the good old fashioned stuffing box is fine.
 
With regard to the very loud banging when in forwards but not in reverse, I had near identical symptoms which turned out to be the cone clutch slipping when engaging forward gear. It was not related to my rapidly wearing cutlass bearings which was caused by a badly aligned engine. We lapped the cones (well a very helpful forumite did) and the banging hasnt happenned since.
 
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