Swan 38 Chain plate inspection instructions

On The subject of chain plate failure as the most likely cause of rigging failures - are there any instructions or drawings to facilitate the inspection of chain plates on Swan 38's?

Best,

Patrick

Dear Patrick
Inspection involves checking visually for corrosion, cracks, and deformation. If in doubt use a magnifying glass. For example Spotcheck can be used to find cracks.
Kind regards
Lars

Many thanks Lars,

Do you have any technical drawings for a s 38's chainplates?

Regards,

Patrick

Dear Patrick
Drawings are hardly needed, if you remove the teak cover the entire chainplate is visible
Kind regards
Lars

Thanks again Lars - I will get some Spotcheck

Patrick

If Chainplates pass through the deck (as opposed to being bolted onto the outside of the hull), the part of the plate that is most susceptible to corrosion is the area completely hidden by the caulking where is passes through the deck.  It is here that the salt water will collect and the corrosion begins.  To inspect this area the plates need to be unbolted, removed and cleaned/polished.  (Do not kid yourself that by removing the caulking you can see.)   I know it is/can be a lot of work but with some of these yachts getting to be 30 or 40 years old it is worth every minute.

I lost one chainplate which broke at the top bolt.  It was this bolt to which the ground wire was attached and the dissimilar metals caused the problem, (with the aid of a leaking chainplate).

David 43/12   

Good tip and thanks - will look at the chain plates with interest. Someone told me that the old Nautor keel bolts are notoriously week - is this fact or a wind up (he was Scottish!)

Dear David and Patrick
Here some additional information.
I am not aware of any case where a chainplate broke where it passes through the deck, but know of two cases where it broke at the uppermost bolt below deck.
It is suggested that members contribute with information if they have experienced such problems.
If there is crevice corrosion inside the mastic as suggested, this will create visible rust oozing out top or bottom, which should alert the owner.
The chainplate has considerably more cross section here compared with the upper end across the turnbuckle pin hole, meaning that some corrosion may even occur without immediately weakening the structure.
If the chainplate caulking is leaking it is likely that the water inside is exchanged at a rate preventing oxygen starvation and thereby crevice corrosion.
Some mastic suppliers provide primers for improving the bonding, and this can be recommended. If the mastic bonds well to the steel water can not get in between.
It is suggested that the reason for the chainplate breaking at the top bolt was not the attached wire. Copper is less noble in the galvanic series and will not corrode stainless.
Instead it is likely there was bending under load causing fatigue with the time. The leakage also indicates excessive movement.
The bolt diameter is probably smaller than the pin diameter at the upper end, and therefore the cross section at the bolt larger. Tension loads alone would then not break the chainplate at the bolt.
For preventing bending loads the chainplates should be accurately aligned with the load to within one degree angle.
Kind regards
Lars

Dear Members
Fortunately nobody contributed with more broken chainplates.
The oldest Swans are now 45 years old, and after such a long time fatigue effects begin to show up. It is therefore increasingly important to regularly check the chainplates and rigging for visible warning signs such as local corrosion and cracks. If in doubt use more sophisticated methods.
Fatigue cracking develops slowly, and there should be plenty of time to detect problems before they become serious.
For getting an idea of the time span before problems can be expected I will do an analysis of Swan 36 chainplate fatigue life. For this it would be very helpful to receive input from owners with information stating the normal heeling angle used on the wind, and how many miles sailed on average yearly, alternatively the total number of miles accumulated.
Best regards
Lars