Tecktalk - Deck Fittings

Dec 1999/Jan 2000 page 3 - by Tom Winlow and Marcel Laroche.

In 1986, when I bought my Viking 33, it required a complete refit. That entailed removing all deck fittings and rebedding them. This year, because I am repainting the deck, all deck fittings have to be removed once more.

As a result, I have noticed that the "miracle" bedding compound that I had used then, has turned to powder in some places and has hardened under most fittings. I also noticed, that it had stuck to either the deck or to the fittings, but never to both. As a result, the last three feet of both genoa tracks leaked and the deck core had to be replaced.

As I am writing this article, I am holding a tube of this "miracle stuff" in my left hand. On the tube, it says in part: "Will not harden, shrink, crack, or dry out". It will definitely harden and dry out. During the refit of l986, I ran out of the "miracle stuff" and I used butyl sealant. Butyl is the sealant that oozes from the hull and deck joint. Wherever butyl was used, there was no sign of water penetration in the balsa core. The butyl under the fittings when they were removed, was still as soft and sticky as the day it was first used. I have started to rebed small fittings with complete confidence, using butyl that has been scraped from the 26 year old deck joint.

Window installers use butyl tape between the thermopane panel and the wood frame as a weather barrier. Because it never hardens and is very sticky, it is able to maintain an effective waterproof seal even if a fitting moves slightly. Butyl tape comes in gray or black and in thickness starting at 1/16 th inch. Use the 1/16 th inch tape. One roll will last a lifetime. When bedding a fitting, press some butyl tape around each bolt hole in the deck, then put some under the bolt head and under the exterior washer. Never put any sealant of any kind on the interior washer and nut, because in the event of a leak, water could be trapped in the core.

Before rebedding anything, redrill each hole to twice the size of the original bolt hole. This will remove any old sealant from the hole and expose fresh core material. Then, plug the hole from below with either plasticine through the hole in the headliner or 2 layers of masking tape if you don't have a headliner.

Cover the affected cabin area with a plastic sheet in case of leaks. Pour epoxy in the hole until flush with the deck. The object here, is to let the epoxy soak into the core of the deck around the hole and effectively make the core watertight. After 10 or 15 minutes, top up the hole with more epoxy, as the core will soak up the epoxy. If a hole takes too much epoxy, stop, there is a leak! Do not use thickened epoxy or filler of any kind for this purpose, as they will not soak into the wood core as well as pure epoxy will. Let the epoxy cure for at least 12 hours, then drill the appropriate size holes for the bolts. You now have a bolt hole surrounded by at least 1/16 th to 1/8 th inch of pure epoxy well bonded to the core and both skins. In the event of a leak, the core is completely isolated from water ingress. This will also prevent the wood core from being crushed when the nut is tightened. How tight should you tighten the nut? Tighten it until the bolt breaks, then back it off one turn!

If your boat is 10-15 years old, it may be time to rebed everything. All this seems to be tedious and overkill. Tedious it is but overkill it is not. I wish that I had known better in 1986, but no one told me.

Things to remember:

  • Never use screws to secure things to a cored deck, because if water penetrates past the screwhead, it will be trapped in the core.
  • Never use sealant on the inside washer as this will trap wa- ter in the core.
  • Drill 1/16 th oversize holes when reinstalling the fittings. This will allow for water drainage in the event of a leak and facilitate the installation of the bolts.
  • Use oversize washers or backing plates. This will better distribute the load and prevent crushing the balsa core.
  • Repairs to a cored deck cost a fortune. Try me for an estimate.

Marcel Laroche.