Merlin chainplate attachment

[Alastair Miller]

I've recently undone the 4 bolts securing the chainplates to the side decks of my Merlin and I was surprised to find that it took very little load on the nuts to undo. Given the fact they they are nyloc nuts I suspect they weren't that much more than hand tight.

I'm looking for advice on how much torque to put on these when I reassemble. I appreciate they shouldn't be overtightened given that the material in between is fibreglass and balsa but I would expect a modestly reasonable amount of tension to be used?

thanks

[mikebuggy]

Areas of stress are usually reinforced by timber or ocassionally solid GRP. I usually tighten chainplate nuts 'pretty tight' using a normal spanner without a tommy bar. Certainly an awful lot tighter than finger tight, but not '16 stone rugby player with 3 ft Stillson' tight. Note that S/S Nyloc nuts are now frowned on in some areas if subjected to damp (ok in the dry). This is because the nylon deprives the S/S of oxygen and can promote crevice corrosion. This is a more important consideration for UW fittings than for chainplates of course, but nevertheless double nutted plain nuts are more common nowadays for all fittings.

[Jolly Roger]

The nuts may appear to have become loose as the reinforcing plywood pad could have had a slow weep and started rotting. I would strongly advise you remove the fitting and check the condition of the plywood. If the plywood has started to degrade then you need to take action now as you could loose your mast.

I suggest using an alum key in a drill to remove any damp timber. Then seal the underside and pour some antifreeze in and leave for 10 minutes. Then drain off and allow to dry for several days as this will reduce the moisture level to an acceptable level. Then seal the bottom of the hole and fill with epoxy and fiberglass strands, making sure it is well compacted. This will act as a new solid core for the bolts to bear on. Then redrill the holes and reseal the fittings. Some advice is in the West guide. http://www.westsystem.com/ss/bonding-hardware/

The above solution should work in almost all cases, but the only other solution is to cut the existing pad out and glass a new one in. Very messy and time consuming and to be avoided if at all possible.

[Alastair Miller]

Thanks for the replies. The reason we removed the bolts was to investigate some cracking in the gelcoat around the chainplates. I'm not sure where I would find reinforcing plywood? The chainplates on my 89 Merlin are flush on the deck whereas a fellow club members' earlier Merlin has chainplates on a raised pad.
Holes were drilled around the chainplate area and investigation showed the deck core was still dry. Some epoxy was injected to stiffen the area before grinding out the cracked gelcoat and applying a new finish. Hopefully we've done enough to resolve the issue.