Everything you never wanted to know about Crevice Corrosion.

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oldgit

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Knew when bought boat about 2 years ago that it had a bit of corrosion in stainless prop shaft immediately next to stern gland.
Not to bothered about drippy stern gland and left it alone.
Opportunity to get shaft made up at local machine shop and as nothing else had gone wrong recently with decided to get lifted out and draw shaft.
Gor Blimey never seen anything like it in your life, the whole nine yards.
Different damage out side stern gland, inside sterngland, inside cutlass bearing and just for good measure the odd deep pit here and there.
The stern gear had all been replaced only about 10 years early after a serious grounding.

First pix inside the cutlass.Next pixs corrosion around stern gland.



 
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I couldn't separate the shaft from the coupling to change a Volvo seal. I tried the blowlamp, a club hammer, a hydraulic press etc with no luck.

So I bit the bullet and cut the shaft in two to get it out. The bit that went into the cutless looked just like that.
 
Have original receipts from when both shafts were replaced after grounding in 2006 under an insurance claim.
Boat was based at Conwy in N Wales but repair was undertaken by a company at Wareham in Dorset.
Not impressed with workmanship either, replacement shafts were really to long and gap between prop nut and rudder stock was only about 25mm..
Size of woodruff key was a joke , far to small.
Quality of stainless shaft is not stated on receipt but assuming was 316.
The boat was lying idle for some considerable time as elderly owner was getting out of boating.
Other shaft is perfect with no sign of wear or corrosion, however it may have been changed more recently.
 
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My own 5 year old shaft suffered 'crevice corrosion' right at the lip seal but it was very minor compared to yours ( but at the wrong place on the shaft) At that time few others reported similar issues so we put it down to the boat being unused for 3 months in oxygen depleted water in Sardinia.
At that time I looked into materials and their costs in case we had to replace. It seemed that although 316 was commonly accepted and used there were much better ( for shafts) grades available at not a lot of extra cash.
If your sort of damage can occur in 'normal' UK conditions then perhaps we should all be considering shaft material more carefully?
 
Would have thought the that those "grooves" in the shaft would have abraded the rubber inside the cutlass but very little shaft play.
 
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