Resealing Chainplates

San Juan 28  Knute  Hull #149

Many years ago we noted that our various chainplate sealing attempts were just not working, and that the upper edge of the starboard bulkhead was getting punky.  Not a good thing. Apparently we weren’t the only ones with this problem, since there was an actual “recall” notice sent out by the Clark Brothers, suggesting that we acquire a longer set of plates to avoid a pull out situation that some had experienced.

Rather than simply going with longer plates, we decided that what we really needed was a deck flange to provide a surface opposing the deck in order to get a better seal.  I drew up a diagram of what we had in mind, and took it to Yacht Constructors here in Portland, OR (makers of Cascade Yachts) for fabrication, including backing plates.

As long as we were doing this I figured more and bigger would be better, so the new design uses (7) 3/8” diameter bolts at the bottom, and (2) more near the top, between the original holes for the (6) ¼” diameter bolts. 

While we were waiting for fabrication, we removed all of the softened plywood, and built the bulkhead back up with WEST epoxy.  Since we were moving all of the loading to the bottom of the bulkhead, we did not get carried away with lots of glass fiber reinforcing.  The final build up included ‘microballoons’ which are easy to fair, and coincidentally a close color match with the shadowy veneers replaced.

The chainplates themselves extend as far down the bulkheads as possible, reaching just above the bench level.  Each Plate and corresponding backing plate is of ¼” thick stainless steel, and the deck flange is 1/8” stainless, attached with a full circumference fillet weld.

The initial installation of these set the bottom of the flange about ¼” above the deck to allow for a proper joint backing and sealant installation.

Our sealing assembly started with 3/8” foam weather seal, sealed to the deck with 3M 5200, around the deck slot.  Then the plates were bolted in, and finally a perimeter seal of 5200 bridging between the deck and underside of the deck flange.  The purpose of the foam is to prevent bonding at the “back” of the sealant joint, so that the sealant is free to stretch, and keeps the tension loading on the top and bottom joint bonds even from inside to outside.

Well as many of you know the hull structure of these boats may be tough, but is a bit flexible under heavy sailing loads.  I’m not sure I can really SEE it, but you certainly can feel and hear the boat flex when letting off a high backstay cylinder load.  This flexing has been enough that even the improved joint would unbond from the stainless plate, although it took a couple of seasons, instead of a couple of weeks to fail as with the original installation. 

So we needed a way of putting a compression load on the deck seal to prevent this tension failure of the seal.  After a couple of years of daydreaming about this problem, I came up with a solution, and tried it on the starboard side.  It has held perfectly for a full year, so I have just done the same on the port side, and documented the process with photos as I went.

After setting up two spinnaker halyards and a jib halyard to the toe rail near the chainplates as temporary shrouds, I removed the plates, removed all sealant, and cleaned up with acetone.

I then installed the foam weather strip around the plate below the flange, and ran a bead of sealant around the perimeter of the deck slot.  This is just a backup to keep the foam sealed to the deck as a “dam” in case the main seal gives out.  I slid the plates down in, and secured the plate in a position approximately 1/8 inch above the final position.  I used a wire tie through the hole around a pair of small bolts as “deadmen”, and it worked perfectly, assisted by the compressive strength of the foam weatherstrip. 

With this preparation, I masked the exposed surfaces of the flange, and the deck outboard of where the seal would be.  I used 3M 4200 this time, as it actually mentions ability to seal to metal, where the 5200 does not.  I got a pretty clean job done with the sealant, for which the taping was a great help.  I let the sealant cure for 4 days before installing the bolts to suck it into final position.

Now for the tricky part: pulling it into final position.  Because the plate is set 1/8” above final position, the bolts do not easily slip in.  What you have to do is pull the plate aft away from the bulkhead.  This allows the bolts to be run through the plate with the bolts angled downward to the bulkhead holes.  Once they are started, they are each threaded in incrementally with a ratchet socket.  The bolts I used have a straight shank, with the threads starting essentially at the fore surface of the bulkhead, so they won’t pull themselves all the way in.

After getting them in as far as they will self thread, the backing plate is hung over them.  A bit of tapping from the back side should get them through far enough to install the lock washers and nuts. Then the final tightening will finish it off.  The two upper bolts can’t be started until the lower ones are tight

The final photo of the deck seal clearly shows the convex form created by the compression.  Should be good for many years to come.

Steve Poland, SJ28 Hull 149, Knute of Portland, OR

Bonus photo:  Pair of line clutches installed on custom stainless brackets.  The tension loads go directly into the aluminum control bridge.  We replaced the wimpy teak backing plate for the control bridge anchor bolts with a pair of stainless “rub strips” to better resist pulling it out of the cabin top.  This is probably the best upgrade we’ve done, as it makes single handing very easy (assisted by the Autohelm).

Steve Poland

polands@teleport.com