Senior Moment Member
Join Date: Jun 2011
Location: West Vancouver B.C.
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Sabreman has the solution for through-deck chainplates (and all other deck hardware). The "trough" he refers to is essentially a rectangular countersink. I have found through experience that countersinking all bolt holes will allow a small reservoir of sealant to collect and act as a recessed O-ring when the fasteners are tightened down. Cutting, sanding, filing or grinding a small facet around the opening for the chainplates will have the same effect, trapping a rectangular "O-ring" of sealant under the cover plate.
I've been doing this for years and never had a failure.
I, myself, personally intend to continue being outspoken and opinionated, intolerant of all fanatics, fools and ignoramuses, deeply suspicious of all those who have "found the answer" and on my bad days, downright rude.