As seen on A Sharp Exit and Dark & Stormy.
Whatever you use to seal the chainplates, they always seem to leak when the boat is ‘working’ in heavy weather. This breakdown of the sealant occurs as the chainplates are bent slightly back and forwards with the rig movement, imposing tensile loads on the sealant which pulls it away from the faces of the chainplates. No amount of cleaning, roughening of the chainplates or the use of expensive two-part polyurethanes with their primer, seems to produce an adhesion which can resist these loads.
This modification puts a welded flange around the chainplates at deck level. The continuous sealant under this will now be subject to shear loads that any sealant is better able to resist. The only difficult part of this process is being able to guarantee the flange is in exactly the correct position when it is welded.
- At this stage, leave your chainplates connected to the boat. Have a machine shop make up the two flange plates in 3mm 304 stainless plate. They should be large enough to project from the sides of the chainplate by a good 12mm all round. Make the slot that allows the chainplates to pass through, an easy clearance to allow for weld penetration.
- Now take the flange plates back to the boat and place them over the chainplates. Space them evenly off the decks by 1 or 2mm with a piece of card to simulate the thickness of sealant that will eventually be present. Now ‘stick’ the flange and the chainplate together with a good fillet of body filler so as to hold the two parts solidly together.
- Remove the chainplate bolts from the bulkhead and lift out the assembled chainplate and flange. Take it to your local specialist welder and explain you want a TIG fillet weld around the top of the flange only and that no misalignment is permissible. Also explain that the chainplate is the load carrying part and no undercut of the weld can be tolerated.
- Return to the boat, add plenty of sealant, push the assembly home and put the bolts back through the bulkhead.