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Sail & Rigging - Chain Plates
21 January 2014 - 17:50
Join Date: 12 June 2007
Posts: 39

Chain Plates
Good Afternoon Lars
Like Patrick Lund in 2012, I too have had an insurance Survey, and been advised of a problem with Mast step support corrosion, and Chainplate staining ? corrosion.
I attach his findings, and a picture of the chainplate , compared to one taken in 2001.
Do I need to remove the mast and chainplates to inspect and rectify both problems at this instant, or would exposing the deck teak and using Spotcheck having removed the bolt covering and drying out the mast support and cleaning in situ be appropriate ?
Billyon Swan 38

Excerpt from Survey 11 1 14
""Are the mast loadings well supported and distributed throughout the vessel?""
No distortion to the mouldings was found at the base of the mast post where it landed onto the floor pad. However the galvanised mild steel plate supporting the mast foot was starting to corrode and now needs to be refurbished before more serious corrosion develops. It is recommended within the next twelve months that the galvanised mild steel mast foot support is cleaned of all surface corrosion back to bare metal and then primed and over coated with a suitable marine steel epoxy paint system or removed and re-galvanised.

""Any evidence of seepage around the fittings below?""

Both cap and lower shroud chain plates below decks had staining and water drips present around the bolt heads and plates. Due to the unknown extent of water damage to the unsighted areas of the bulkhead covered by the chain plate and the teak covering panels, it is recommended that the through
deck chain plates, spreading plates and the fixing bolts are removed and the areas behind the fittings are further inspected for any unsighted water damage to the wooden plywood bulkhead or crevice corrosion to the fittings . After this the area should be appropriately dried, repaired and the chain plates re- assembled with new flexible bedding sealant “Sikaflex 291 or similar

Chainplate 01&14

21 January 2014 - 20:26
Join Date: 02 January 2008
Posts: 1547

Dear Alasdair
Thank you for the information.
The surveyor is right, in order to inspect the bulkhead it is necessary to remove the chainplates. At the same time they can be examined for crevice corrosion. When reassembling take care to make abt. 5 mm slots in the deck around the chainplate lugs for the mastic, and check if the mastic supplier recommends the use of a primer on stainless for better adhesion. Both reduces the risk for leakage.

If you can access the mast step corroded areas it should be sufficient to clean and paint them. It would also be important to check that the mast shoe drain holes are open, and that the mast lower end has not corroded inside the shoe.

It appears that in your area the insurance actually inspects the vessels, that's not the case everywhere.
Kind regards

21 January 2014 - 22:19
Join Date: 12 June 2007
Posts: 39

As ever , thankyou Lars

23 January 2014 - 07:17
Join Date: 25 July 2012
Posts: 30

Hi Alasdair,

I am in no way contradicting Lars and I know you only addressed your query to him but I would like to give you my opinion.

Regarding the chainplates, yes they must be removed.   It is the heel plate that has my attention.   If the surveyor saw corrosion there is a distinct possibility that the hidden parts of the plate are also corroded and very possibly there is damage to the base of the mast itself. 

If you do not have a water-tight barrier inside the mast to stop water coming down, you will have both fresh and salt water inside your mast at the bottom: a probable cause of corrosion inside.    If you do have a barrier then the water in the bilge not only gets on the plate outside the mast but will go inside through the drain hole(s).    All this to say the mast must be pulled to better know and, if necessary, treat the problem.

I do not know the setup in the Swan 38, I am just basing my opinion on experience with boats in general so I may stand corrected.


David 43/12

23 January 2014 - 09:31
Join Date: 12 June 2007
Posts: 39

Thankyou David
All information is welcome, will have a look at the chainplates first and no doubt more questions will arise!

23 January 2014 - 12:52
Join Date: 02 January 2008
Posts: 1547

Dear David
Thank you for your comments.
Referring to the mast lower end it could be mentioned that S&S Swans do not have a water-tight barrier inside the mast originally, and therefore also shavings from the halyards will collect in the mast shoe, and possibly block the drain holes partly or fully.
If water is trickling out slowly this will keep the mast shoe and step wet for long times, and cause additional corrosion.
It is advisable to flush out the mast inside and shoe occasionally with fresh water through a halyard exit, and check that the drain holes are fully open.
It has been mentioned before that it is advisable to enlarge the drain holes considerably - a strong updraft is created in the mast when the sun is shining, and this helps to keep the bilge and interior ventilated.
Kind regards

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