Index

FORWARD HATCH - Reseal.
INDEX - Replace Seal, Replace Hatch, Install Lever Handles, 2 Framed Hatches, Drill & Cut Techniques (Vent).

REPLACE the FORWARD HATCH - The factory forward hatch of the SJ23 is made from smoke tinted acrylic, 3/8" thick by (23 5/8)" square and 1/2" radius corners, (10mm thick by 60cm square).  It is installed flush to the deck, inside a deck recess.  The SJ26 and the original SJ28 use the same design.   Its unfortunate there is no metal frame to strengthen it.  The aluminum strap hinges are through bolted to the acrylic with a flat washer behind each nut.  It is OK to use this technique for a single mounting bolt, but if two or more bolts go through the same piece of acrylic, as is the case with the SJ23 strap hinge, then the hardware must allow for thermal expansion of the acrylic and the stress associated with operation, to distribute the forces uniformly around the hinge bolts.  Drill the bolt holes 1/32" oversized and replace the individual washers with a single aluminum plate, the same size as the hinge plate.  The larger holes allow movement and the two plates will sandwich the acrylic, thereby distributing the stresses evenly and greatly extending the life. 

You can expect an acrylic hatch to last about ten years, but some last beyond fifteen years.  It all depends on how it was machined during the installation, used/abused during its life and the amount of UV light it was exposed to.  While a new 3/8" thick acrylic hatch (without a vent hole in the center) is strong enough to support a person, in a fatigued or stressed state it takes far less force to break it.  You could increase the strength by replacing it with a 1/2" thick acrylic combined with a 1/4" thick spacer under the deck strap of the hinge.  In Panache's case the original hatch was 26 years old when it cracked from the central vent hole to one of the latch bolt holes.  This crack was likely due to a combination of factors: age, stress cracks created by the crude hole saw I used in 1996 to install the 3" Nicro solar vent, the very tight holes the factory drilled for the latch bolts, or the occasional time I stepped on the hatch when it was not reinforced with a wood ring around the vent hole.  Combine these factors with the 75⁰C seasonal temperature range we undergo on the Canadian prairies and it is inevitable the hatch will crack.  I temporarily sealed the crack with electrical tape for a couple of years, which kept out most of the water, but I also had to place a towel on the cushions to absorb the drips.  Problem is, a large broken hatch can lead to a dangerous situation in a storm, so it was time to do something about it.  But this was also a good opportunity to rethink the original design. 

Choice of Material & Fatigue - One might think that Lexan (polycarbonate) is a better material for a hatch than Plexiglas (acrylic), since it can stop a small bullet and withstand a whole range of impact without breaking.  This property makes it excellent for security purposes.  While Lexan is much stronger than acrylic when new, after about five years of exposure to UV light the properties cross and the Lexan becomes weaker.  This is because standard polycarbonate absorbs UV and therefore doesn't stand up to UV light while acrylic filters UV.  This is the reason why polycarbonate yellows with time and acrylic stays clear.  There is a some controversy over this subject.  GE Polymer, the company that manufactures Plexiglas and Lexan, advised me this is rubbish.  They said, "Lexan is stronger than acrylic, if it is coated with MR-10".  My guess is that this opinion still stands with those people who are unaware of MR-10 coating.  Regardless of which situation it is, Lexan has a few other properties that you should consider; 

• it has a higher coefficient of thermal expansion at 3.9⁵ in²/F⁰ than acrylic at 1.3⁵ in²/F⁰. 

• it scratches easily (without MR-10 coating). 

• is more expensive. 

When buying Lexan be sure to specify MR-10 coating that makes it resistant to scratching and UV).  If you more strength than 3/8" acrylic, use 1/2" Lexan and install a couple of 1/4" thick spacers under the deck side of the hinges so the Lexan lies flat on the hatch seal.  Despite the controversy around the choice of materials, I would choose Lexan with MR10 coating to replace the forward hatch.  This would be my current choice if I have to replace the hatch.  Good luck finding the smoke tinted stuff.  It was very popular back in the 70s when most plastics shops carried it in their inventory.  Today (2006) you will have to buy a whole (4x8)' sheet for $600 CA just for your (2x2)' hatch.  Share the cost with somebody on the skipper list or consider tinting the clear stuff at an automotive shop.

2018-08-12 - I found a piece of 3/8" clear acrylic in my garage so cut it to size and gave it the standard treatment for fabricating a replacement hatch.  The wood support ring for the vent was eventually permanently installed.  So far all is OK.  At right is the forward cabin with the new clear hatch.  Notice how bright it is.  Watching stars and satellites is a real treat. 
2019 - At the end of the season I have not found the clear acrylic to be any hotter than the original tinted stuff.  If anything it is a bit cooler.  Doesn't seem right to me though.  It could be that the clear acrylic doesn't radiate heat.  However, there isn't as much privacy. 
PS: WD40 sprayed on the old protective paper coating makes a very effective removal agent to dissolve the adhesive.  Especially if you leave it soak for several hours or overnight.  The paper was easily nudged off with a razor blade pusher and a subsequent application removed the remaining adhesive.  TOP 
 

LEVER HANDLES for the FORWARD HATCH - All SJ23s, 24s, 7.7s & early 28s hatches are equipped with an acrylic hatch that pivots on two aluminum strap hinges.  The other models are likely the same.  The hatch is locked from inside the cabin with two screw knobs.  I really dislike these screw knobs in that it takes way too many turns to open or close them.  It should be noted they are difficult to operate when the seal is compressed flat to the deck.  With a new uncompressed seal the screw knobs release with only a few turns.  I discovered this after I replaced the seal.  Then there is the odd crewman who has a difficult time figuring out which direction to twist the knobs, counter clockwise to open and clockwise to lock!  Something to do with never having been taught how to read an analogue clock!  Personally, I hate being exposed to the solar heat under the hatch as I twist the knobs.  If the boat is bouncing in a seaway, the motion while you are looking up at the knobs can be nauseating.  Definitely not a fun part of the job!  Then there is the fact that the factory latches can't be opened from the outside.  After all, doors have a handle on BOTH sides, so why not a hatch?  I know of many San Juan owners who are equally fed up with the factory screw knobs.  On the other hand, there are sailors who like them for the tight seal they create since the closing pressure is fully adjustable.  I guess it all depends on your preference.  While a latched hatch may be excellent for theft prevention, I wonder if you can get out fast enough in an emergency.  The lack of an outside knob is a safety issue during heavy weather sail changes when it would be much quicker and safer to stuff a bagged jib through the hatch than to walk it back to the cockpit.  This is exactly the weather condition in which latches should operate quickly and be operable from both sides.  The quicker you can close and latch the hatch, the safer it is, especially if you sail solo or the other crew is busy.

TAYLOR LEVER HANDLE - Well time, patience and friendship has paid off.  While I was building a prototype lever handle, my sailing buddy Doug found some very suitable handles on the web at a reasonable price; Taylor stock # 1731.  The advantage of people working together to solve a common problem.  The handles fit on an SJ23 acrylic hatch with very little modification to the existing hardware.  The best part is that they can be operated from the outside if the handles are purchased with the exterior thumb levers.

Doug installed a set on his new 1/2" thick hatch and they aligned to the existing striker plates at the front of the opening which is obviously critical.  I have since installed two sets of handles: one on Panache's original 3/8" thick smoked hatch as shown at right and the second on Panache's replacement clear hatch.  It is a bit more challenging to install it on the original acrylic since I had to seal the old holes before drilling new holes, to ensure the acrylic is not weakened.  Regardless of the thickness of the acrylic, this Taylor handle requires an additional cylindrical (white PVC tube) spacer to make it fit on an acrylic hatch.  The PVC spacer in visible at right and in the parts photo above.  The wall thickness and diameter of 1 3/8" OD white PVC tubing (plumbing section of home renovation store) fits exactly into the circular groove around the bottom edge of the handle.  The groove ensures that the spacer is held captive and stays centered for secure support and smooth operation.  Both are crucial to maintain a tight seal and minimize strain on the acrylic. 

INSTALLATION - If your seal is no longer pliable it is recommended to install a new one first.  Once I discovered how high the new gasket holds the acrylic I decided to add shims under the strap hinges so the acrylic lays flat on the seal with minimal compression next to the strap hinges.  Then I installed the striker plate on the under side of the deck.  Next, cut the length of the PVC spacer so the handle will fit to the striker plate.  The PVC tubes should be approximately 5/8" long, depending on how tight you want the hatch to seal (and how much strain you want the handle to hold).  Finally determine the location of the hole to install the handle so it fits to the striker plate while turning freely. 

PROP UP HATCH - I use a short stick to prop up the hatch.  A 6" stick at the mooring or anchor and a 2" stick while sailing in very calm weather.  Although it is usually closed while sailing.  The advantage of a stick is that if something should snag the lid, then the stick drops and the lid closes, undamaged.  If I used one of those springs the lid might get damaged.  If I loose a stick overboard, its no big deal.  I just go to the bush and grab another one.

NOTE:  Because it may not be obvious to some people which direction the handle must be operated, it is useful to add a 1/4 circle arc glued to the bottom of the acrylic to indicate the operating sweep of the handle.  You may be in that same frame of mind when panic sets in and your are inverted under the hatch!  TOP 
 

INSTALL an ALUMINUM FRAMED HATCH - If you really want to improve the hatch then install a commercial submarine style framed hatch.  They seal so much better, operate quicker and are much stronger than the factory hatch that you will wonder why you didn’t install one years ago.  Price may have something to do with it though!   On the other hand 3/8" smoked acrylic is scarce today, making it expensive.  Besides the fact that they are totally water tight, the acrylic floats stress free inside the frame and is therefore not prone to crack like an unframed piece of acrylic.  This is the main reason why a solid acrylic hatch is weaker than an aluminum framed hatch.  Most framed hatches are equipped with two dogs (levers) to latch it and a riser to support it open in any position.  Some hatches can fold back to lie flat on the deck.  The more expensive ones have low profile exterior knobs to open/latch the hatch from on deck, a bug screen to keep mosquitoes out, and a double acting hinge to scoop air in or suck it out.  Some even have a second notch for the dogs to latch to the deck frame so it can vent some air while keeping loose fingered people out.  I have used this feature on a rainy day and it really does prevent stuffiness in the cabin while retaining some cabin heat.  The only redeeming feature of a San Juan factory hatch is that it is flush with the deck and doesn't cost a lot.

Since no commercial aluminum framed hatch fits the 20” square opening of an SJ23 you will have to buy a slightly undersized hatch and fabricate or buy a transition spacer to mate the hatch to the deck hole as shown at left.  (the diagram is not drawn to scale, but it demonstrates the concept).  Making a spacer isn't as difficult as it looks.  It consists of a square wood frame that mounts on the top perimeter of the deck opening, raising the hatch flange about ¾” above the deck.  Teak is an excellent choice but if you are good with any other material, well fill your boots.  Make the outside dimensions of the spacer NO bigger then 22 ¼” square to retain the drainage function of the trough around the hole.  Round off and slope the top outside corners of the frame to prevent toe injury or snagging things.  Fit the inside of the spacer snug against the frame of the hatch as shown above.  Raising the hatch slightly with a transition spacer adds an additional feature of blocking some solid water out of the cabin when the hatch is open.  This is helpful when rinsing the deck with a bucket.  You should also add a wood filler frame to the bottom of the hole (cabin ceiling) to add form strength and appearance; strength being the more desirable of the two!  The top transition spacer seals the hatch to the deck, the bottom spacer adds the strength to the sandwich.  For ultimate strength the hatch frame must be through bolted to the deck to sandwich the mating frames and deck.  Countersink the screw heads and seal the holes with tapered wood plugs to prevent corrosion.  Seal all joints with Sikaflex and coat the wood frame with Sikkens Cetol Marine.  Some hatches also have a cosmetic trim that installs inside the hatch opening, creating a smooth lining to prevent snags on clothing or sails.  Remember to allow space for this.  The inside trim may also incorporate a bug screen or sliding shutter for shade.  Be creative. 

At right is a Lewmar 60 Ocean Series hatch that was installed on Opus.  The original hatch opening had to be enlarged a bit to make it fit.  "Since the deck at that location is only about 3/8" inch thick, the hatch was through bolted for strength and a teak trim was added underneath to cover the nuts and bolt ends.  This also made a good location to fit a bug screen.  The hatch is self supporting.  It can be opened from the outside and locked from the inside.  The hatch is kind of pricey but definitely worth it."

LEWMAR OCEAN 60 HATCH - This Lewmar hatch is a very neat installation.  It requires a 20" by 20" hole, only slightly larger than the factory acrylic hatch requires. 

After removing the old hatch and hardware, scrape off the old gasket, then clean all around the hatch perimeter with a Scotchbrite pad.  Make a plywood template of the new hatch by drawing a pencil line on the plywood around the perimeter of the new hatch.  Cut out the template with a jig saw.  Center the plywood template over the deck opening and draw a pencil line around the template to draw a cut line.  Before cutting, mask off the bottom side with plastic sheet and masking tape to keep the fibreglass dust out of the cabin.  Then use a jig saw to enlarge the hole to fit the slightly larger hatch.  Mine needed only a 1/4" trimmed off each side.  The hole should only be cut large enough for the new hatch coaming to fit into the hole with a very slight gap all the way around.  When satisfied with the fit, use a sander (with vacuum hose attached) to smooth the edge.  Then use the hatch as a template to make a pencil mark at each drill hole around the perimeter of the hatch where the bolts will be installed.  Remove the hatch then drill the holes, being careful not to punch through too hard to prevent chipping the back side (I think I used a 7/32" drill bit).  A wood backing block will prevent chipping.  With the area around the hatch and holes vacuumed and cleaned, use a penetrating epoxy to seal the deck core along the cut edge and butter each drill hole with a little brush.  Penetrating epoxy will wick into the core and not fill up the drill holes.  After the epoxy has cured the hatch can be installed.  I used closed cell foam weather stripping applied to the underside of the hatch flange to create a seal.  No.10 pan head SS bolts with a washer and crown nut on the cabin side worked well.  On my boat the deck thickness varied greatly along the perimeter of the hatch so the No. 10 bolts varied from 3/4" to 1 1/4" in length.   If the weather stripping is squished evenly all the way around, then the bolts are tightened evenly.  Brian King, SV "Partez!"

An alternative to a costly aluminum framed hatch might be to build a similar frame from wood.  Fasten the corners with epoxy, float the acrylic inside the wood frame and seal it with Sikaflex.  The hardware can be thru-bolted to the wood frame without concern for expansion or contraction stress on the acrylic.  The biggest advantage is that it can be sized to exactly fit the existing SJ23 hatch opening.  Levers can be attached to the wood frame.  I know of several people who have built a hatch just like this and have no problem with it.  Just food for thought!

Below is a summary of the critical dimensions for selecting a commercial hatch. 

• The deck opening is 20” square.

• The hatch deck flange must be no larger than 22 ¼” square on the outside. This relates to a 1" wide flange! 

• The hatch deck flange must rest on top of the teak spacer, not exceeding 22 ¼” OD and the downward lip must fit inside the 20" opening.   TOP 
   

It requires a hole that is only slightly larger than the factory hole. 

                          Tim Woods

DRILL & CUT ACRYLIC TECHNIQUES (VENT HOLE) - When installing an acrylic pane inside an aluminum frame there must be at least 1/4" space around the edge for thermal expansion and sealant. Similarly, there must be a space around a bolt installed through acrylic.  Regardless of how the acrylic is installed, observe the following procedures to prevent stressing it; 

  CUT

• VENT HOLE - DO cut a vent hole with a centering router to 1/8" oversize radius.  Cover the acrylic with masking tape to protect the surface.  All outside edges of the hole must be chamfered with a router to prevent stress cracks.  The optimum tool to cut a large diameter hole is a hole saw, then a router and lastly a jig saw.  If you use a variable speed jig saw cut with a very slow speed.  If you cut fast the acrylic will liquefy and it will weld itself behind the blade, which will require a second or third pass to split the cuttings.  This is the biggest draw back of using a fixed speed jig saw.  However, a blade with zero set sharp teeth has less of a tendency to liquefy acrylic or create stress cracks. 

• SPIDER CRACKS - To prevent future spreading and damage, sand the inside of the hole, bevel the corners and coat the cut edge with SCIGRIP Weld-on acrylic cement.  This stuff can creep inside tiny cracks created during cutting and fill any scrape marks to a smooth surface.

• MANDATORY SUPPORT RING - If a 3" or 4" diameter hole is cut through the acrylic for a (Nicro) vent, then the strength of the acrylic MUST be restored with the addition of a wood support ring, shaped like a flat doughnut.  Make the thickness of the doughnut equal to or greater than the white protruding plastic liner of the air hole, (white on inside of ring).  Cut the ID of the hole in the wood ring so it fits snug around the plastic liner.  Cut the OD of the doughnut equal to the diameter of the vent hood so you don't see the dust collected on the underside of the vent.  This is not a problem if you fall asleep quickly on the V berth!  Instead, you see a nice finished wood ring!  Glue the ring with Sikaflex or silicone sealant to the bottom of the acrylic.  Clamp it there with C clamps for 24 hours. 
  While the wood ring finishes off the inside very nicely, the real purpose is to stiffen, straighten and minimize the flex of the acrylic.  When I clamped it for my dry fit I noticed that the ring immediately straightened the acrylic to completely flat.  Quite a nice surprise that I didn't expect.  Without a wood ring, the unsupported acrylic will droop down with time/heat and each step on the hatch.  Eventually it becomes a very shallow pan.  The pan shape compromises the strength and it will crack.  If the hatch does crack, you can repair it with SCIGRIP Weld-on acrylic cement.  The stuff really does work and leaves no trace if you are careful with application.

 DRILL

• BIT TYPE - DO NOT use a drill bit designed for wood or metal.  These bits will pull into the acrylic and you risk cracking or chipping the material.  They also liquefy the acrylic and will bind if you stop the bit in the hole.  While you can use a dull bit and turn it backwards, the best drill bit to use is a "Craftics" bit which is made for plastic.  They have a 70⁰ bevel on the cutting edge.  The sharper point reduces the stresses introduced into the hole wall and imparts a fine finish without clouding or crazing the wall of the hole.  If you intend to use a standard metal bit, then regrind the tip to have 0⁰ rake on the cutting edge.  This scrapes the hole instead of cutting it and therefore it cannot bind when exiting the acrylic. 

• PRESSURE - DO use very light pressure when drilling acrylic.  It is possible to crack or chip the material by forcing the bit with too much pressure.  When drilling a hole (vertical ), the weight of the drill is all that is necessary.  Be patient and give the bit time to do its work.  You should see fuzz coming from the bit, not a long spiral.  If the bit is pulling spirals from the material you are using too much pressure.  Use higher drill speeds on small holes and slower speeds on larger holes.  Better yet, drill a pilot hole followed by the final size which is called step drilling. 

• BACKING BLOCK - Always use a backing block of hard wood to prevent the drill from cracking the acrylic as the drill exits the back of the hole.

• HOLE SIZE - DO drill oversize holes.  Acrylic expands and contracts more than the fasteners so oversize holes are required to allow for expansion and contraction.  The general rule is to drill the hole at least 30% larger than the diameter of the fastener.

• BEVEL - DO use a counter sink bit to chamfer or bevel the shoulder of the hole. Sharp edge acrylic tends to be a stress riser, create redial spider cracks emanating from the edge. So bevel all sharp edges.  This also applies to all outside edges as well.  You can use a sanding block with fine paper (150 grit or finer) to finish the edge. Do not flame smooth the edge.  This weakens the acrylic.

  BOND

• METAL - The mating surface between flat metal bolted to acrylic must be sealed with at least 1/16" thick Butyl rubber, Sikaflex or equivalent marine sealant.

I would venture that if these precautions are taken, the hatch should be free of cracks for your grandchildren.  But if you have to make a whole new hatch from acrylic it is likely cheaper to buy a framed made marine hatch as shown above.  3/8" smoked acrylic is not readily available today like it was in the 1970s, making it scarce and expensive.  You can bet that a glass company or plastic supplier will charge for a whole sheet.  You also require all the tools to machine acrylic.  TOP 
 

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