Swan 57 mast step

Dear all,

I am hoping that someone maybe able to confirm or refute a rumour that I have heard, from various sources, concerning corrosion of the main mast on early Swan 57s. Apparently in some models the main mast step has stainless steel which causes galvanic corrosion of the mast. This has led to at least one rig failure.

I do not want to sound alarmist as it is a rumour, and we all know how well our beautiful yachts are made. However if the Professor has any words of wisdom I would be grateful.

Kind regards

David

I am not aware of rig failures but I can confirm that in 2002 (23 years after birth) on my 411/004 the lower mast end was affected by corrosion due to what you mention: steel/aluminum galvanic corrosion.

I must add that the condition was not considered serious at the time but in order to avoid future problems it was fixed by inserting and fastening an aluminum properly shaped sleeve inside the mast.

It is a safe attitude to check often that part in all sailboats because it is a well known issue and, luckily enough, it is easily discovered.

I understand that putting a sheet of plastic (e.g. PTFE) between the mast and the step may prevent corrosion but I do not know how effective and lasting this is and if the electrical insulation would produce other problems.

Daniel, 411-004 Luna Menguante

Dear David

I would suggest that the mast shoe around the lower end on top of the step has been stainless. This does not automatically generate corrosion, standing water is also needed, and by taking care that the shoe drain holes are open this can be avoided. It should be noted that wear on the halyards cause shavings to collect at the bottom of the mast and this tends to block the drains. Enlarging the drains can be recommended, this would also improve ventilation of the bilge.

Referring to insulation is does not help to put plastic on the sides only, it is needed also under the mast, and the compression loads there are very high, a sheet of high fiber content GRP laminate would be better.  As the mast is supposed to be grounded for lightning protection it would then be appropriate to connect it with a cable to the step. Connecting cables to keel bolts which are wetted by bilge water will result in unsightly corrosion, and it is better to make the connection high up so it does not normally get wet.

Lars

Thank you Lars and Daniel for your replies and suggestions. I have always ensured that the mast step is clean and dry and though there is some galvanic corrosion on the step itself it is not anymore than I would expect for a 30 year old fixture.

I am glad that there is not a known problem.

Thanks again

David 

Hello David

I have had the same thoughts about the base of the mast on my SS 47 from 1980.  Few years ago, I had the mast down and, although there were very little corrosion, I had the base rewelded with fresh aluminum. After that, the base and the fixture were thoroughly cleaned and painted with different coats that are suitable for metal. There is a ventilation whole at the base of the mast. I attached a hose to that and allowed its other end to take/discharge air from the middle section of the bilge. That is all I did and the wole thing looks very nice until now.

Perhaps this can be of some help?

Cheers/Philippe

Dear Philippe,

That is very interesting and I have her out of the water at the moment so I may lift the mast for a better view. I suppose I should not forget the mizzen either. I like Lars's idea of a GRP mat but to connect a cable to the keel bolts would be  huge undertaking as water tanks, table, batteries etc are covering this area.

Thanks for your information

Salute

David

Hello Lars,

I have checked my mast step again and as far as I can see the step is galvanised. It is difficult to see due to the corrosion, but I think I do have corrosion coming from the inside of the mast and will probably need to replace the step, shoe and possibly weld the bottom of the mast. I will post a photo as soon as I can. She is hull no. 2 if this helps understand the step design.

Always good to hear your feedback, kind regards

David