The mast step (an anodised aluminium) piece was also deformed and visibly corroded.Therefore I decided to replace as much as was feasible. After all, a new mast would cost about £6000!

To deal with chainplates and other deck or mast hardware your first stop should be your local metal fabricator. 

It is most efficient to remove the old hardware, take them with you, write down all important details, and have them all replicated at the same time. 

In a marine environment corrosion resistance is of the utmost importance. It is critical to specify that the new steel pieces are made of 316L Stainless Steel, or an appropriate aluminium bronze alloy. Never accept inferior steel alloys like 304/A2 or 18/8. Aluminium pieces should be remade with a corrosion resistant aluminium alloy and if feasible, anodised.

If your shop can electropolish the steel pieces then this should be done – otherwise you will have to do this yourself. Bear in mind most original fasteners will be Imperial sizes but metric replacements are easier to source – except for rigging screws.

Tools  Required:

Socket set with various socket sizes

Usual hand tools – hammer, chisel, hacksaw, pliers, wrenches etc

Allen keys,  Portable power drill with usual bits

Multi-Tool with various blades

Drill Press, HSS drill bits, Stepped drill bit

Bench grinder with polishing wheels (coarse and fine)

Materials:

Replacement 316 Stainless fasteners, nuts, washers - mostly A4 M6/M8 Set Screws Hex Head

Super Stainless (or citric acid), Penetrating oil, Marine Grease

LocTite, Sikaflex 219i,  Epoxies and fillers

Aft Chainplates:

These are easy to remove and are just through-bolted through some thickened glass into the lazarette.

I didn’t replace these – they seemed in good enough condition - but I did replace the bolts and washers, going from original 1/4” set screws and thin penny washers to M8 part threaded bolts with thicker washers. 

The original bolts are – in my opinion – undersized and were visibly bent when I removed them.

To do this I first removed and cleaned up the chainplates. I then enlarged the bolt holes with a drill press at home. After buffing and polishing with my bench grinder, I reinstalled them with Sikaflex to seal.

I measured the distance from the inside very carefully and drilled through the strake from the outside to get it the bolt out. The chainplates then came out easily enough. I cleaned up the holes left for later reattachment.

I noticed that the plates which were weeping rust had a lot of pinhole corrosion on the bottom of them and also where they came through the deck - this is common, and dangerous as crevice corrosion can eat away the stainless from the inside.

I also observed also that the chainplates had elongated attachment holes for the turnbuckle clevis pins. This is because they are M10 holes but the typical 5/16” turnbuckles only need approximately M8 diameter clevis pins.

If you want to avoid this in future make sure new ones have appropriate diameter holes for your rigging screws. (Rigging screws are still usually Imperial measurements! Always measure twice with a callipers before doing anything!)

My fabricator reproduced the chainplates from 316 Stainless using the old ones as templates. I made sure to enlarge the bolt holes to M8 for added strength with bigger 8mm bolts. I rounded off sharp corners to avoid stress risers.  

Note that if you try to do this yourself that there is a bend in the main shroud chainplates that must be accurately recreated using appropriate heat and a press. This may be tricky if you want to use some bronze alloys instead of stainless.

When reinstalling do a dry fit first. You may find out – as in my case – that the new chainplates don’t have a snug fit in their old sockets. I used WEST System epoxy and 406 filler to ensure a proper fit by applying it on the inside of the old “socket”, and covering the chainplate with tape and grease on the side which met the epoxy filler. 

Then I lightly fitted the chainplate over the filler and only removed it when epoxy had set enough. The form then fits the chainplate exactly, and when epoxy is fully cured you finally attach the chainplate.

It is important to take care that the new fasteners are a correct length, and that Sikaflex 291 or similar is used to seal all entry holes. Not being fastidious with sealant WILL result in a leak!

Forward Lower Chainplates

I replaced these but retained the basic design – except that the new plate was full 5mm thick plate rather than being a thin plate with a penny washer welded to it as was the case originally. (An interesting case of “penny-pinching”…) Note the attachment holes for the clevis pins were 8mm on these, even though the other chainplates were 10mm. 

At least on mine… your boat may vary. Exterior mounting makes these simple enough to replace. 

Don’t forget to passivate any stainless items before installing them. This involves using an acid (like the “Super Stainless” product or citric acid), washing it off and neutralising it (with baking soda).

It is also important to use LocTite on nut threads – as there is considerable strain and vibration on a boat. 

For safety I generally used Nyloc locking nuts, or two standard nuts if that was not possible. Mostly I used A4 M6 or M8 Hex Head Set Screws, and I opted for thick A4 washers as the originals were thin and often deformed. 

Replacing all the chainplates in one job should be less than £500.

 Useful References

--"This Old Boat" by Don Casey  

--"The Complete Riggers Apprentice" by Brion Toss

--"Hints and Advice" by Selden 

-- Blue Wave Marine Catalogue: 

-- Plastimo Catalogue: