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S&S Swan Maintenance - Shaft Log

02 September 2013 - 17:35 #1 Post Reply
Shaft Log Dear All, At the advice of the Professor, I removed my shaft log (this is part of a much larger project which includes entire new drive train) and recently sent pictures to him for review. Here is what he had to say: Professor: "There is some pitting on the outside of the tube, this means water has been standing under the hose at the forward end for a long time. Maybe the hose clips were not tight enough, or the hose uneven, and the crevices not filled with mastic. The term crevice corrosion refers to this situation when there is a narrow slot with water trapped inside, and this can cause corrosion on stainless steel as the photos show. Finally and silently the tube would corrode through here, and this can be a catastrophe if it occurs at a bad time, could sink the boat if nobody is around. Pitting on the inside of the tube has apparently not occurred here, this is feared more because difficult to see. Sea water is standing inside the tube, and if the water is not replaced there is a lack of oxygen with the time, and this could cause the same pitting. The water is slowly replaced when sailing, but if the boat is standing for a long time in a basin, possibly in polluted water, there may be hidden corrosion problems. Drip-free shaft seals usually have a small connection for cooling water, intended to supply water to a Cutlass bearing installed in the stern tube, but this connection also takes care of replacing the water in the stern tube whenever the engine is run. Very good if you have a stainless stern tube. It would be good to present the photos and comments on the Forum, and suggest that members having stainless stern tubes should sometimes remove the hose and inspect the outside and also the inside, the forward end is likely to be more vulnerable. Your new GRP stern tube does not have these potential corrosion problems." I have attached pictures of the removed shaft log to this note and will attach pics of the new grp shaft log to the next. All comments are welcomed! Chris Top - interior connection Bottome - interior connection exterior - below waterline exit

02 September 2013 - 17:35

Post Reply

ccolton

Join Date: 15 April 2011
Posts: 393

Shaft Log

Dear All,

At the advice of the Professor, I removed my shaft log (this is part of a much larger project which includes entire new drive train) and recently sent pictures to him for review. Here is what he had to say:

Professor: "There is some pitting on the outside of the tube, this means water has been standing under the hose at the forward end for a long time. Maybe the hose clips were not tight enough, or the hose uneven, and the crevices not filled with mastic.

The term crevice corrosion refers to this situation when there is a narrow slot with water trapped inside, and this can cause corrosion on stainless steel as the photos show.

Finally and silently the tube would corrode through here, and this can be a catastrophe if it occurs at a bad time, could sink the boat if nobody is around.

Pitting on the inside of the tube has apparently not occurred here, this is feared more because difficult to see. Sea water is standing inside the tube, and if the water is not replaced there is a lack of oxygen with the time, and this could cause the same pitting. The water is slowly replaced when sailing, but if the boat is standing for a long time in a basin, possibly in polluted water, there may be hidden corrosion problems.

Drip-free shaft seals usually have a small connection for cooling water, intended to supply water to a Cutlass bearing installed in the stern tube, but this connection also takes care of replacing the water in the stern tube whenever the engine is run. Very good if you have a stainless stern tube.

It would be good to present the photos and comments on the Forum, and suggest that members having stainless stern tubes should sometimes remove the hose and inspect the outside and also the inside, the forward end is likely to be more vulnerable.

Your new GRP stern tube does not have these potential corrosion problems."

I have attached pictures of the removed shaft log to this note and will attach pics of the new grp shaft log to the next.

All comments are welcomed!

Chris