NOTE: I originally posted this November 2017 on Sage Marine’s BLOG. In a short time the BLOG will be closed – stupidly. I am reposting this information so it is not lost.
Your sailboat’s deck hardware should have been installed using a bedding compound. (I sadly write ‘should’ as I have worked on boats where there is no evidence that bedding compound was used!) Commonly used are Sikaflex’s 291 and 3M’s 4000 and 4200 (remember, 5200 is for under the waterline applications that will very very very likely never be removed). SPECIAL NOTE: do not use silicone to bed deck hardware! 99.99% of the time silcone has NO PLACE for use in the marine environment!
Bedding compound isn’t forever. It does, slowly, loose its effectiveness. In high loading areas, such as the tabernacle, chainplates, bow plate and bow pulpit the working of the fixture causes the bedding compound to release from the part and/or deck. Water gets under the piece and a series of bad things happen: crevice corrosion (ie, stainless steel rusting), leaks (ie, water dripping on your head) and wet core material (ie, balsa).
Currently in the Sage Marine shop we are servicing an older boat (not a Sage). The boat is built 12 years ago so all bedding compound is suspect (I would write the same about a 12 year old Sage). The tabernacle showed all the signs of the bedding compound had failed as rust was seeping from under the fixture. After removing the bolts holding the tabernacle in place the fixture fell off as the bedding compound was no longer adhered to metal nor deck.
Looking at the part it was clear that bedding compound was used; BUT the tabernacle fasteners were overtightened and most of the sealant was squeezed out. Next the on-deck side of the fastener holes were not beveled to create a ring of bedding compound. Third the wire run for the mast lights was installed in a suspect way for a boat that will have its standing rig raised and lowered multiple times – the wires ran up through the center of the tabernacle. The wires were quickly broken from the mast being raised and lowered (which happened often as the boat is a trailered variety) and the hole the wires ran through wasn’t adequately sealed.
I suspected the core was wet and I hoped that by overdrilling the fastener holes I would find dry material … nope, the core was mush throughout the base.
The solution is to completely remove the core material and ‘start over’. I installed new core and then layered on a new top layer of fiberglass and gel coat.
The new fastener holes are over-drilled and then filled with thickened resin –
Once the resin had cured correctly sized holes are drilled and then beveled.
The tabernacle is now back in place and even if the bedding compound fails (just a matter of time because of the loads in raising, lowering and the boat sailing) any water will drip into the cabin but NOT get into the core. When the drip is noticed the owner can remove the piece, clean up, and reinstall with new bedding compound (about a one hour 1/4-day job v. 5 hour multi-day job to rebuild the area).
So … do you know the condition of your boat’s deck fittings’ bedding compound? If there is any evidence of leaks, rust coming from under the fitting, water drips in the cabin or the nut and washer on the bolt rusting, it is time to remove, inspect (hopefully not repair) and re-install.