SJ23 Tech Tip B15, (Updated 2019-09-03) Bob Schimmel


Repair and Seal a Delaminated Cockpit Locker Lid.
INDEX - Repair 1, Repair 2, Repair 3, Seal the Lid.

The cockpit seats (or locker lids) will take a beating over the years because they are built relatively light to save weight.  Its amazing they are still strong enough, considering the foot traffic they get.  The cockpit floor, by comparison, is built very strong as it's probably the most used surface on the boat.  A seat has to support a lot of weight when a person steps on the middle of it while boarding the boat.  They're likely carrying a box of beer which adds more weight, but who's complaining.  Then there are those 'mad dives' from the top of the cabin into the cockpit during rough weather.  You solo sailors may be aware of this technique.  Well it's no wonder the seat fatigues.
I may be going out on a limb by saying this, but if you have to pick a design weakness in an SJ23 it's the fact that this lid leaks and is not strong enough to stand up to the traffic!  From what I've been told, all San Juan SJ23, 24, 7.7M and 28s suffer from this weakness. 

As with most problems there are complicating factors. In this case there are four parts:

  1. The depth of the down turned lip at the back of the lid, (hinge side), is not deep enough to stiffen the lid sufficiently.  In Clark's defence, there is very little room to make the lip deeper.  On the other hand the drain wells could have been built wider and deeper to accommodate a deeper lip with faster water flow.

  2. On some boats the down turned lip was cut off too short, removing structural beam support right where it is needed.  This creates a large gap along the back of the lid that allows water to flow into the locker.  If this is the condition the hinge is likely not positioned exactly perfect, there is undue stress created on the lamination.  Evidence of this can be seen when you step on the lid and you see it flex at the hinges.  The lid must rest on the complete perimeter of the opening for full support and sealing.  It should not hang in the air, suspended from the hinges.  If you are inside the locker when the lid is closed you would see the air gap between the lid and the top of the opening.  Observe this with someone in the cockpit to latch the open the lid for you.  Hope you trust them!   While you are inside the locker, draw a pencil line on the inside of the lid, outlining the perimeter of the opening.  It will be used later to position a rubber seal.

  3. The flat top of the lid bakes in the sun causing thermal stress.  If a pin hole or a crack exists in the surface from flexing as described in #2, then water will penetrate into the core, causing vapour stress.  Panache experienced a similar problem, from wood screws that penetrated to the balsa core.  The screws were used to mount a strip of wood on the front turn of the lid.  No sealant was ever used under the wood.  I'm guessing this is a factory option since I have seen the strips on other SJ23s.  I found them very uncomfortable and removed them, which is when I discovered the problem. 

  4. If you store the boat in freezing weather, the expanding ice will delaminate the skins as it did on Panache.

You can tell if a seat is delaminated by how much it flexes under weight.  If it deflects from the force of your hand so you can see a definite depression, then the core in your seat is likely delaminated and the wood may be rotten.  Spread a little water on the seat and watch it flow to your hand in the depression.  Under severe delamination, you can hear a gritty scraping sound if you place your ear to the inside of the lid and flex the lid.  This is evidence that the balsa core and the glass laminates are rubbing against each other instead of sticking to each other.  Not good!  Another technique is to listen to the lid as you knock on it with your knuckle.  "Hello anyone home?"  It sounds dead instead of solid.  A good seat feels hard, firm and has a definite ring to it while a delaminated seat produces a dead thud.  You can confirm your suspicion with a moisture meter.  If you've never used one before you owe it to yourself to do so.  You will learn a lot about wood.  Despite the fact that about 70% of my seat was delaminated it still supported me.  Continued abuse would surely result in me falling through it one day.  So what to do?

SOLUTION 1 - An easy way to stiffen the hinge side of a locker lid is to attach a reinforcing strip of wood on the bottom as shown above.  It's a lot easier than widening the fibreglass lip at the back that the factory cut too narrow.  It also prevents future troubles by adding strength.  A formed strip of wood, similar to a handhold on a coach roof, is stiffer, lighter and stronger than a solid piece of wood.  If it fancies you, the holes in the handhold can do double duty by hanging a rag, lines, etc.  Fasten the stiffener to the lid with Sikaflex or 3M5200.  Epoxy breaks free due to the flexing.  However, a stiffener is not a solution for a delaminated lid!

Port seat stiffener - 36" long, installed about 3.5" from the back edge of the lid. 
Starboard stiffener - 34" long, installed about 3.5" from the back edge of the lid. 

SOLUTION 2 - Another solution is to use the delamination repair technique that the Gougeon Bros developed.  They recommend drilling 1/4" holes into the damaged area, about 1" apart, drying the wood core with hot air and injecting epoxy into the holes to seal the core and bond it back to the laminate.  This technique preserves the cosmetic finish on the outside so the repair is visible from the inside only.  This is the technique I used on PanacheNo that's not measles on the right.  The advantage of removing the lid is that I could flip it over so gravity could pull the epoxy down into the holes. 

"I drilled the 1/4" holes into the bottom of the lid, through the balsa core and stopped on the inside of the glass/gel coat surface, therby protecting the outside finish.  The lid is about 3/8" thick overall so I used a stopper on the drill bit to limit the depth to 1/4".  In practice I found it quite easy to stop against the inside of the top laminate because the glass was so much harder than the balsa core, making it easy to feel.  Operate the variable speed drill on low speed.  After all the holes were drilled (I lost count of how many) I scraped the chipped gel coat off the surface because they can cause real nasty splinters and I didn't want them imbedded in the final finish or in my hands.  I also picked the debris out of the holes and vacuumed them clean so the core could dry out completely.  The balsa core was so wet that I dried the lid by suspending it over a furnace hot air register for a month. 

Unthickened epoxy was injected with a Majestic 412 disposable syringe designed for this job.  They are inexpensive and the "needle" is tapered so you can cut the end off to match the hole size to accurately meter the epoxy, spilling very little.  You'll find that you have to fill each hole several times as the epoxy soaks into the core.  This is normal and it pays to have patience.  The inside laminate of my lid was warped in several areas so I injected extra epoxy into these areas.  As the epoxy welled up in the adjacent holes it was the sign to stop filling.  At this point the hole was about half full. 
Then I wiped up the excess epoxy, covered the holes with a sheet of wax paper and centered the squeezing frame on top.  To squeeze the laminates together I placed a hydraulic jack over the frame and used a long (2x4)" to reach the basement ceiling.  A few strokes of the  pump created exactly the pressure I needed to squeeze the laminate together.  Besides creating an absolutely flat surface on the inside of the lid, this technique ensured a good bond and spread the epoxy uniformly.  An unexpected surprise that I'm sure will preserve the wood."  CAUTION: Don't overfill the holes as the excess epoxy will flow to the surface when the laminates are squeezed together. 

I kept the whole works under pressure for 24 hours while it cured and discovered that most of the holes required further filling.  This is to be expected as the epoxy soaks into the core wood so I topped them off with thickened epoxy.  Later I applied a layer of glass cloth.  When the epoxy hardened the inside surface was ground smooth with a hand grinder (do this outside).  A coat of white enamel spray paint restored the surface to an acceptable finish!  I also reinforced the lid with a wood strip as described in solution 1.  If done correctly the lid will no longer be mushy and it will probably last through WWW III, or at least the next dive into the cockpit!"

SOLUTION 3 - It may seem like a major job but replacing the wood core completely may be the easiest and best solution.  It all depends on the degree of damage to the balsa core and how you feel about doing the work.  Use a hand grinder to cut through the inside surface along the perimeter of the balsa core.  (SAFETY - DO THIS JOB OUTSIDE AS IT'S INCREDIBLY MESSY & WEAR A MASK TO PROTECT YOUR LUNGS & SAFETY GLASSES TO PROTECT YOUR PEEPERS).  Once the cut is complete, remove the inside laminate and pick the balsa core out.  Discard the mess since the wood fiber is broken down.  Besides, you now have the opportunity to install marine plywood or rigid foam both with tapered edges and rounded corners.  (Keep in mind that you MUST MAINTAIN the original thickness at the perimeter of the lid).  So if you want to add additional thickness do so in the open area of the locker.  Cut a new piece of filler to completely fill the old hole.  Dry fit to ensure it fits snug, making sure that it does not warp the lid.  Pre-soak the filler, especially at the edges, and the inside of the lid with unthickened epoxy.  Set the filler inside the lid and squeeze the laminates as in solution 2 above.  Once cured, fill any voids with thickened epoxy.  Smooth the edges to create a nice taper.  Cover the inside of the filler with fibreglass cloth to complete the sandwich construction.  Paint the inside surface white and you have a professional finish.  I would still add the reinforcing strip to the bottom as described in SOLUTION 1 above.

Regardless of which solution you choose, consider the job done, as you now have a lid strong as a dance floor! 


NOTE 1: I used a Wagner L609 portable moisture meter to measure the % humidity in the wood core.  This meter uses electro-magnetic force (EMF), that passes through the fibreglass surface inductively, to measure water mass.  With it you can measure precisely where the water is located and the % humidity, hence the extent of the problem.  While the meter is calibrated for Douglas Fir the finite accuracy of the reading is irrelevant.  Simply find a spot that you know it to be dry and compare the wet area to the dry area.  My dry wood measured 5% to 7% humidity and the saturated wood measured greater than 20%.

NOTE 2: The following is the factory warning label that was affixed to the inside of the port lid. 


If used as a fuel compartment ensure adequate ventilation.
(Coast Guard requirements are contained in the Motor Boat Act of 1940).


SEAL THE LOCKER LIDS - Now that you've repaired the lid it's time to do something about the water that collects in the port locker.  Have you ever wondered where this comes from?  Rain can accumulate only so high on the seat while the boat is heeled and if a pail of water is dumped on the seat it disappear very quickly.  In either case the water flows into the channel at the back of the lid, overflows through a 1/4" gap at the back of the lid and then into the locker.  All this because the channel can't drain when heeled (low side) and the lid wasn't sealed to the locker at the factory.  However, when the hull is level, the channel can drain almost any rain.  Dew isn't a problem.  Typically the channel has dirt in it, slowing the flow, but that is a minor part of the problem.  The starboard locker is usually not a problem since it is sealed to the hull; unless you removed the bottom of this locker (Tech Tip B02) in which case this lid must also be sealed. 

The solution for both locker lids is to seal the hinges to the deck with butyl rubber and seal the lid to the locker with Metro Weather adhesive backed Camper/Topper seal.  This (1.25 X 3/16)" weather strip is designed to be used as a cushion on top of a truck box to protect the painted surface from a truck camper.  It is a general purpose flat EPDM (ethylene-propylene-diene-monomer) adhesive backed gasket material for air, water, & saturated steam.  It has excellent resistance to ozone, sunlight, oxygen, acids, alkalis, ketones, and aging due to severe weather, making it ideal for a boating application.  There are lots of other style gaskets sold for this application but EPDM excels in all categories.
NOTE - Camper/Topper seal is sold in the US by Autozone, part # MW11425 and in Canada by NAPA, part # 770-1763 as Camper Tape.

While the automotive industry has used hollow gaskets for years, the marine industry seems to stick with the woefully inadequate, solid cushiony neoprene foam that stays compressed after the load is released.  It generally leaks after a season of use because it doesn't have the resiliency to spring back to original size to effect a seal due to the extremely small pores of the foam.  While the EPDM may also not spring back in this application, the fact that the foam forms around the lip will mean that it developed a seal.

The best place to install the weather strip is on the bottom of the locker lid, pointing down.  The lid offers maximum surface area for best adhesion.  Besides, the top of the locker lip is usually very irregular and too narrow in places as shown below due to the freehand cutting of the hole at the factory.  If it is installed on the lip, it will get beat up with every trip into the locker. 


- To determine where to stick the gasket on the underside of the lid, crawl inside the locker, close the lid and draw a pencil line outlining the perimeter of the opening on the inside of the lid.  Stick the gasket on the lid, in a straight line 1/3" inside the pencil line.  This lets let the lip contact meander across the face of the gasket ensuring a seal at the perimeter. 

- This truck camper cushion gasket is 3/16" thick.  This is about the correct thickness to just fill the gap which should push the lid up, ever so slightly.  This way the gasket isn't crushed with the lid closed, a position in which it will spend the majority of it's life.  The thickness is critical so take your time fitting the gasket.  If the gasket is too thick it will prevent the lid from closing and strain the hinge screws.  The seal will develop an indentation with time resolving both problems.  If the gasket is too thin it can't seal the lid.  To effect a seal at the back, double the thickness of a rectangular seal by sticking one layer on top of the previous.  If the gap at the back of the lid is that wide it could explain much of the water in the locker.


  • Clean the bottom of the lid with acetone.
  • A gasket on the lid doesn't block access to cleaning the channel at the back.
  • A gasket on the lid will be out of the way with gear going in and out of the locker.
  • It is easy to clean any debris sticking to the gasket.
  • A wide gasket on the lid is sure to seal somewhere on the meandering narrow lip of the locker.
  • And finally, it actually works!!

If you think the gasket will stick to the locker lip, spray it with silicone lubricant or install some 1/8" thick nylon coated neoprene using an adhesive called SEAMGRIP.  The nylon faces the gasket.  Time will tell if you will need this.  Also note there is a double layer of foam along the hinge side.  This is usually enough to seal the gap.

Below is a hinge sealed with butyl rubber that was left untrimmed for this demonstration.  The excess was later trimmed with a razor knife.  In hind sight, the majority of water that leaked into the locker flowed through The unsealed hinges.


HINT - If there is water in the "sugar scoop" aft of and below the cockpit, it came from the gudgeons, transom chain plate (bolts & deck top) or cockpit drain fittings.  Confirm which side by looking for dribble marks on the bottom of the hull.  If the "sugar scoop" is dry the water came from the locker lid hinges (include screw heads), gunwale fittings or scupper.  You can reach the sugar scoop with your right hand by kneeling on the cockpit sole.  The water that flows into the port locker from a leaking scupper flows down the cabin wall to the settee shelf, through the port bulkhead and into the locker.  Its amazing how much water can flow through leaking hinges since they easily work loose due to the unsupported lid.  Run your hand under the hinges to feel the dampness.  If you opened the bottom of the starboard locker (Tech Tip B02) the water drops from the leaking hinges to the bottom of the locker, then flows to the settee and accumulates under the cushion on the settee. 

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