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The worst possible nightmare for a San Juan 21 (other than sinking) is core rot.  These spunky little boats have a deck constructed of two layers of fiberglass with end grained balsa sandwiched between.  When holes are drilled in through the deck to hold on hardware, (rails, hatch covers, etc.) it provides the opportunity for water to get between layers and begin the cancerous process of rotting out the balsa.  Once started, the enivitable end of this process is a mushy deck, unsafe for sailing, likely to cost more in blood and gold to repair than just getting a new boat. 

I decided that my very first project on Limpet would be to permanently seal every single deck fitting hole such that core rot would never claim this little boat.  To do this I became a master at what might essentially be considered Boat Dentistry.

There are several great articles on core rot in San Jan 21s and I was on the lookout for it when I purchased SJ21 #759.  The way you look for rot is by pushing on the headliner (inside cabin) around hardware bolts, or places where holes have been drilled through the deck in the past.  If there is any give to the headliner, the core around that fitting is likely rotting.  When I inspected Limpet I was pleased to find no softness in the hull.  However there were quite a few spots where holes had been drilled for deck hardware long since removed.  The holes were filled with sealant, but it didn’t look like a good permanent solution to me. 

1. The first step in my project o permanently solve this issue was to pull off everything on the deck: hand rails, cam cleats, eyes, jib car tracks, blocks, hatch rails, EVERYTHING.  This is best done as a two person job.  One on the deck with a screw driver to hold bolts, and another in the cabin with socket set connected to a cordless drill on low speed.
2. Next I drilled out every hole using a 1/2 inch bit (make sure to use a twist or lip & spur bit not a spade bit).  Between the holes which were currently holding hardware and holes which had once held hardware there were over 60 holes in the deck of my San Juan 21.  This is a risky proposition during a rainy Seattle Winter.
3. Next I bent a 16 penny nail into an “L” shape about 3/8 inch in from the point of the nail.  I clipped off the head and locked the long end of the nail into the chuck of my cordless drill.  I then used the bent nail to knock out the balsa core around the holes I drilled.  Here is where you are hoping to see nice white balsa wood… If you have dark brown wet mush your deck is rotting.
4. Next I covered the freshly drilled holes from the inside with blue painters tape, and mixed up some epoxy.  I filled holes with epoxy (5-8 at a time so I had a small batch of epoxy and enough time to work with it).  After letting the epoxy seep into the balsa for a couple minutes I poked holes in the tape and drained epoxy back into the cup I mixed it in.  Strait epoxy is great at bonding to wood and fiberglass, but is brittle when cured which is not good for holding on deck hardware.  So at this point I added high density filler to the epoxy (which also had some balsa hunks in it that came from the hole when I drained the epoxy).  I added as much filler as I could without turning the epoxy into paste because I still needed to pore it.  Finally I put new painters tape over the interior holes, and poured the epoxy + filler mix into the holes so that it was mounding up on the outside.
5. When the epoxy cured I scraped the top level to the deck and pulled the tape off the interior.  I now had perfect “Fillings” for all the “Cavities” in my boat.  I drilled holes through the fillings for deck hardware confident that even if water gets under the bedding sealant, it will just leak into the interior of my cabin, not destroy my balsa core.
   The last step was to bed all the hardware with a good marine sealant.  I used Sicaflex and was sure to clean my deck and hardware with lacquer thinner before applying the sealant.  I put hardware on finger tight and waited 24 hours before cranking down on all the nuts and bolts.  This puts the sealant under compression and keeps water out. 

The bad news for me was that several of the holes I drilled out had some dark brown, wet, rotten balsa.  I don’t have the desire to actually cut out bad sections, and replace them.  I am not sure if the rot will continue too spread, or if my cutting off the water supply will keep Limpet safe.  I may have signed Limpets death warrant by not appropriately dealing with the 3-5 holes… but only time will tell.  For now she is a much dryer boat than when I got her.

What you are in for if you need to re-core your deck:

• Quasar Re-Core
• Bow Re-Core

Here is a good article on bedding deck hardware:

• Bedding Deck Hardware
  

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