SJ23 Tech Tip B04, (Updated 2021-04-07) Bob Schimmel

 Index

Companionway Sliding Hatch
  INDEX - Hatch Glides & Keepers, Storm Hood with Acrylic Slider & Seal the Sliding Hatch.
 
When an SJ23 sliding hatch is closed, the down turned forward edge laps only slightly over the sill at the front of the companionway opening.  This creates a poor seal, letting water or rain with any force to readily find its way under the hatch lip, over the sill, and to dribble into the cabin.  This a weak design of an SJ23, but having said that Panache has only leaked water twice; once during a brutal storm and another while towing in the rain.  Another problem with this design is that the hatch slides directly on top of the gel coat on the deck.  Add a bit of dirt to it and the abrasion is significant.  Shown below is a standard SJ23 hatch.  The 3/4" air gap between the deck and the hatch lip is typical.  Other SJ23s may have a slightly narrower gap which is purely accidental.  I think the size of the gap is determined by whoever trimmed the excess off in the factory!  While an SJ23 is certainly not an offshore sail boat, it is quite capable in some pretty rough coastal waters or lakes.  It would definitely be more water tight if the sliding hatch were sealed better. 
 



 

 

 

Double baffles generally don't work on a sliding hatch.  Instead, a better solution might be a storm hood or a "hatch garage" like on an SJ28.  This is usually made from a fibreglass cover that is sealed to the deck along its front and sides.  In these pictures you can see the obvious advantage of having a hood to deflect solid water that comes over the deck.  Imagine how much water would end up in the cabin of an SJ23 with the large gap that the factory creates. 

A storm hood equipped with a translucent slider will solve the problem and enhance the character of an SJ23 cabin.  The front of the sliding hatch becomes watertight and you get an unbelievable amount of light below, even when the acrylic slider is closed.  Bright light is always appreciated in cloudy weather.  With this modification, the acrylic slider is removable for cleaning and it operates dead quiet on the UHMW glides.  Shown at right are cutaway drawings typical of a SJ23 factory style hatch (left) and a sealed hatch on the right.  You should design this upgrade so the inside of the hood is easy to access for cleaning.  The top of the hood will likely be strong enough to hold line lockers, cleats, or a person.  The latter depends on your weight!  As a bonus, a storm hood makes it much easier to seal a dodger to the deck, add a small dorade type vent for inclement weather or to mount a solar panel.   TOP

 

CONSTRUCTION - UHMW GLIDES & ALUMINUM KEEPERS
STEP 1 - HATCH GLIDES, Add UHMW glides under the hatch so it slides dead quiet on the slippery surface instead of grinding the gel coat away.  Steps 1 & 2 may be performed independent of the rest of the conversion.  They are an excellent modification on their own right. 
  1. Remove the factory teak keepers by drilling out the wood plugs with a 3/8" brad drill bit.  If you're careful, the bit will clean out the hole without destroying the head of the screw, so you can still remove the screw.  Remove each 1.5" #8 Roberts wood screw.  Set the teak keepers aside.
    (Brad bits are designed to drill a flat bottom hole while leaving a clean edge for inserting a wood plug.) 
  2. Lift the sliding hatch off the deck and place it in a safe area.  Use acetone to clean the hatch deck tracks.  Seal the old keeper mounting holes with epoxy or a marine sealant like Sikaflex. 
  3. Install two strips of UHMW (1/2x1/8)" 54" long where the hatch slides on the deck.  Use 3/8" #8 flathead SS screws recessed slightly so the hatch slides over the screw heads without touching them.  Remember to drill a pilot hole in the fibreglass to prevent stress cracks.  Apply a thin coat of marine sealant to seal the holes and prevent marine growth under the UHMW glides.  The inside edge of each glide is chamfered to match the slope of the deck track.  If you only have partial length strips of UHMW then make a tapered joint between the sections.  This way the hatch does not go "bump" as it slides over the joint.  Put the hatch back in place and test it for free movement for the full length of the travel.  You might have to sand the bottom of the hatch to smooth any high spots.  No sense in prematurely wearing the UHMW. 
    (Ultra High Molecular Weight) is a tough, rigid material that is impervious to moisture.  It machines well with power tools and does not liquefy or plug the cutting edge of the tool.  It should be available at a plastics supply house). 
  4. If you will not be building a storm hood then fasten a good quality hollow sponge foam weather strip to the front of the companionway sill to improve the water tightness when the hatch is closed and to deflect water when it is open.  The seal must make contact across the entire front of the hatch.
  5. Re attach the teak keepers unless you intend to install aluminum rails as in STEP 2 below.  TOP
STEP 2 - ALUMINUM KEEPERS, Change the teak hatch keepers to aluminum. Definitely a must if you install a storm hood. 
Install the two (1.75 x .25 x 55)" flat aluminum rails. 
  • Drill holes through the aluminum.  Counter sink the holes for the pan head wood screws.  You may as well drill the screw holes at equal spacing about 9" apart so it looks good.  The factory screws are seldom spaced equally. 
  • Wash the protective oil film from the new aluminum keepers using acetone.  Roughen the surface with 600 grit sand paper and prime it with zinc-chromate.  (Wear a mask as this stuff is lethal for your respiratory system).
    Paint it with two coats of flat or matt paint.  Black to match the toe rails or white so it stays cool in the sun.  (If you use glossy paint, it is apt to reflect the bright sun light in your face). 
  • The alternative to painting the aluminum keepers is to powder coat or anodize them. 
  • Drill a pilot hole in the fibreglass for the mounting screws.  They prevent stress cracks.  Use 1" long #8 SS flat head wood screws to fasten the keepers to the deck pods. 
  • Use marine sealant to seal the holes. 

NOTE - Despite what it look like, the deck under the sliding hatch is not flat.  It is convex.  For this reason you must leave a bit of a gap under the keepers otherwise the hatch may jamb in the track.   TOP
 

CONSTRUCTION - STORM HOOD with ACRYLIC SLIDER

At right is a picture of the factory equipped storm hood on an SJ28, Lady Lass.  A hull that is in many respects similar to an SJ23.  This gives you an idea of what the San Juan storm hood design looks like. 

For early vintage SJ23s equipped with teak hatch keepers this modification consists of all the following steps;

  1. Install strips of ultra high molecular weight (UHMW) glides on the deck to slide the hatch  on. 
  2. Install two aluminum keepers to keep the hatch over the UHMW glides.
  3. Convert the old hatch to a storm hood.
  4. Build a curved acrylic slider.

NOTE - If you intend to build a storm hood, you must convert the wood keepers to aluminum to prevent wood rot under the hood.  You should also allow for ready removal of the hood to service the acrylic slider and to clean the area under the hood.  TOP

STEP 3 - STORM HOOD, Convert the factory hatch to a storm hood.
There are two methods of converting the old hatch to a storm hood.  Regardless of the method, you must seal the front and sides to the deck to keep out water and growth. 

The first method is to determine where you want the hood fastened to the deck, then extend the sides and front of the old hatch with new fibreglass.  Do this over a temporary mould.  Follow the steps in the image at right.  The new side flanges must fit snug to the deck as shown on the SJ28 above. 

  • Fasten the hood to the deck with stainless screws and seal the perimeter using a rubber gasket as you may have to be remove it for occasional cleaning.  You could be inventive here and imbed stainless nuts in the deck to fasten the storm hood. 
  • Be sure to seal the deck balsa core with epoxy around each screw.  Failing to do this will lead to a  quick demise of the balsa cored deck. 
  • Use gel coat of matching or contrasting colour to cover the glass repair work on the front and sides of the hatch.  If you can't match the colour, sand it smooth and paint it.  Perhaps the same as the cove stripe.  TOP
STEP 4 - ACRYLIC SLIDER, Create a water tight sky light.
Make a new slider (sky light) from 1/2" thick acrylic.  Match the tint to the colour of the forward hatch or use a pale blue or smoke colour.  Do not use clear acrylic due to the heat gain and the fact that it shows scratches too easily.  A new acrylic slider might be a challenge to make due to the curve of the cabin roof.  To obtain a matching curve in the 1/2" acrylic, it is necessary to heat and bend it.  The required temperature is easily reached with an outdoor gas barbecue.  A commercial pizza oven would be perfect, but do you know of a pizzeria willing to loan their oven?  Instead, make your own temporary oven to place on top of a barbecue.
  • Construct a four sided box out of strand board as shown at right. 
  • Wire it together at the corners.  Do not rely on glue as the heat will release it.
  • Taper the sides outward from bottom to top.  Size the bottom to fit to your barbecue. 
  • Install two 3/4" dowels to support the mold.  Extend the sides of the mold to include two side "feet" that will slide on the UHMW tracks and lift the slider up about 1.5" to clear the sill at the front of the companionway opening. 
  • Make the hatch wide enough to extend to the inside edge of the hatch rails to keep the hatch centered between the rails. This prevents jamming. 
  • Lay the lid loose on top of the box. 

Lay the acrylic panel on a felt covered plywood mould just beneath the lid where it is warmest.  Acrylic typically becomes soft at around 1700C and will droop quite freely over a felt covered form.  It should bend in about 15 minutes with the BBQ on high.  After it has formed to the mold shut the heat off to let it cool slowly with the lid closed.  (SAFETY NOTE: Keep a fire extinguisher handy).

  • Attach a teak handhold to the back top of the slider and a hasp for locking. 
  • It might be wise to add a downward pointing lip to the front just to flow the water on the deck.  A garden hose will determine this very quickly.  You could also add a couple of stopper bolts at the companionway end of the rails to prevent the slider on board. 

Enjoy your new watertight skylight and dead quit slider.  Now you can get up in the middle of the night and open your hatch without disturbing the crew.  There might even be enough light so you don't have to switch a light on!  TOP

CONSTRUCTION - Close the Gap on the Front of the Sliding Hatch with a Water Deflector & Seal. (2005)

WATER DEFLECTOR - This deflector is an alternative to a storm hood to keep water out of the cabin by lowering the forward lip of the hatch so it skims just above the deck to deflect the majority of the water.  Think of it as a cow catcher on the front of a locomotive that deflects an animal off the track.  The addition of a hollow rubber gasket glued to the front of the sill stops the bit of the water that manages to slip under the deflector; provided the hatch is pulled back tight against the gasket.  The deflector and the gasket go a long way towards sealing the front of the hatch to make the cabin more water tight and mosquito free.

Your choice of material for building the deflector is basically dependant on your skills and tools.  You could use 1/8" thick stainless steel which would look quite nice when polished.  Cutting 1/8" stainless steel could be a tough job though.  You might also use fibreglass but you must match the colour of the aging gel coat, which could be difficult.  I chose to laminate strips of wood, matching the pattern and colour to Panache's grab handles.  It is coated with Sikkens Cetol Marine, the same coating that is on all the other wood trim on Panache.  The deflector is glued (silicon sealant) and screwed from the inside through the lip of the hatch with flat head screws, backed by a length of (1x1/8)" flat aluminum (think large washer).  The flat head wood screws ensure that the inside of the hatch can rest flush to the rubber seal on the sill.  Its not too difficult to bend aluminum (in the difficult direction) using a bench vice and a 5 pound sledge hammer.  The hatch lip is sandwiched between the deflector and the aluminum, making a very strong joint. 

The advantage of using a laminated wood beam against the lip is that if a person steps on the hatch, the wide foot print of the lamination supports the weight on the deck.  If stainless steel is used then the thin sharp edge will likely gouge the gel coat on the deck. 
I should add that the forward lip on Panache's hatch is only slightly deeper than 1" and therefore quite weak to support a person.  It is laced with micro-fissures and had a crack through the middle.  The shallow depth of the lip is probably the contributing factor to why it cracked in the first place. 
The combination of laminated wood and the aluminum strip has stiffened the lip to maintain the bow in the hatch.  After the beam cured I could not measure any flex! 
I no longer step on the hatch with the solar panels installed there. 

When making a curved laminated beam from different colours of wood, the contrasting edges reveal any left/right symmetry errors, so accuracy is paramount.  If you have to shape the beam differently on one end than the other (wrong curvature), such as sanding through to the second layer, you will be left with a none symmetrical pattern that will stick out like a sore thumb!  A perfect fit starts with a symmetrical template that can be confirmed by folding it over on itself.  The thinner the laminations the more accurate you have to be.  Remember, is you screw up at least make it look intentional.  You have to be creative here.  Sometimes a job is more art than engineering! 

Shown above are the laminations clamped in the form while the epoxy cures.  The final beam was cut to size and rounded at the corners to conform to the hatch and deck.  Regardless of how perfect you cut your wood, the final shaping to match the hatch is what changes the end result from amateur to professional.  Below are the inside and outside views of the dry fitted assembly. 
      

The completed lamination is coated with epoxy.  Sealing wood with an epoxy barrier stabilizes it against warping, stretching or shrinking.  There are four coats of Sikkens Cetol Marine over the epoxy to preserve it.  This achieves the same look as 12 coats of varnish.  Although I now have one more section of bright work to maintain!  One thing for sure, it deflects a lot of water as the boat is hauled down the road in the rain.  I have not seen any water inside after a road trip through the rain.  This deflector is a perfect place to do some customizing so I applied the "San Juan 23" logo to the front, adding art to form! 

As a side note, we once hauled the boat home through the rain and were forced to camp in the boat at a mosquito infected rest stop.  A "difficult camp out" was made extremely miserable with the rain water that entered through the hatch.  What a mess to clean when everybody was dead tired, wanting to sleep.  Never again.  This event was the only justification I needed to construct this water deflector.

 

 

 

SEAL - A few years after I made the water deflector (2005) I removed the hatch to clean the slide tracks.  That's when I stuck the hollow foam seal to the front of the sill to keep the last bit of deck water or rain on the road out.  It also makes for a soft landing when the hatch is closed.  The foam seal solves both problems quite nicely.  The surface is a bit nasty looking in these photos since its difficult to wipe clean when it is freezing outside.

       
 

 

 

HATCH SLIDES - During the winter of 2021 I took the sliding hatch home to install new flexible solar panels.  A nice winter project to keep me busy during COVID lock down.  When the hatch was reinstalled in Spring I replaced the aging 1/4" thick UHMW slides with 3/16" thick puck board.  This is the maximum thickness that should be installed to keep the hatch between the curbs and ensure smooth sliding.  The 1/32" made all the difference in smooth sliding.  Also, use one piece of puck board so the hatch doesn't go "thump" over a joint.  That's tacky construction.  Seal the bottom to prevent marine growth then fasten with 3/4" flat head screws every 8".

   
 

The holes that secured the previous rigid solar panels and the new flexible solar panels were sealed with epoxy.  Then the non-skid surface was painted white to protect the epoxy and match the panels.  I also painted the aluminum rails white.

HINT - The bit of deck under the forward corners of the closed sliding hatch accumulate a lot of dust and debris over many years.  Without removing the hatch these spots are impossible to clean.  It's probably a good idea to remove the hatch and clean the deck every few years.  TOP
 

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