Drilling holes.

[Skippa]

Need a bit of advice. As much as I hate drilling any holes I needed to drill four holes for button snaps in my 1980 DSII to secure a new boom tent. Two holes in the transom and one on each port and starboard coaming. I started with a 3/32 bit on the coaming and found that too small so I went to a 7/64th. When I started to screw in the snap I cracked the gel coat and pretty good size piece broke away. I plan to repair it with a bit of gel coat repair. The other three screws went in without any major damage. How can I avoid this cracking on my next project? (Barber outhaul cleats)
Thanks in advance.
Kevin

[K.C. Walker]

Drilling holes in fiberglass needs to be a pretty precise fit. There really is not much give, and especially no give in gelcoat. The best defense against snapping screws or stripping out the fiberglass is properly sized holes and self tapping sheet metal screws. As to the gelcoat, countersink the holes to relieve the stress on the gelcoat.

It takes a little more time but I think it's worth it. You can drill the holes so that the threads just catch, then mix up some epoxy, put it in the hole and wax threads before inserting the screw. This makes a really good strong (and sealed) screw hole. This method works well for through bolting, as well. As long as you wax the bolt or screw you can remove them without problems.

[Skippa]

Thanks K.C.
I did use marine grade silicon sealant but will give the epoxy a try on the next project.
As always, I appreciate the input.
Kevin

[GreenLake]

K.C. didn't mention the other reason why countersinking holes is good - it allows a thicker bead of sealant than squeezing it against a flat surface. That allows the caulk to work across a larger amount of movement by the fitting. This, and many other things having to do with drilling holes, are described in gory detail on this web site.

http://www.pbase.com/mainecruising/sealing_the_deck&page=1
Some of this relates to cored decks which don't necessarily exist on the DS, but would apply to drilling holes through any plywood cored transoms, for example.

[Alan]

Great link, GreenLake, thanks. It's perfect timing - I'm about to drill some holes in my transom to install a motor mount. Among other things, this helps me work up the nerve to actually take drill to fiberglass.