Forward Hatch

By Todd Schlemmer:
The original hatch on the bow of the San Juan 21 is a serviceable fiberglass lid until it breaks, cracks, or leaks. Gene Adams of Port Gardner Sailboats, (206) 696-8685, sells a forward hatch “kit” – some assembly required. This kit includes the hatch plate, latches, gasket, and hinges. I found the hinges too long for the mounting blocks I fabricated, but some creativity might allow you to use a longer variety. I reused the spring support from the old hatch.
For this project you will want:
• Acrylic hatch panel
• Stainless strap hinges
• Gasket material
• Stainless strap hinges
• Hatch support
• Stainless Steel bolts, washers and (lock) nuts
• Woodworking tools as needed for hinge blocks
• Measuring tape
• Contact cement
• Waterproof sealant / adhesive (3M 4200)
• Anhydrous rubbing alcohol (for removing 3M 4200)
• Masking tape
• Safety equipment – eye, hearing, and respiratory protection, gloves?
NOTE:  These instructions specifically apply to a 1974 Mark I.  The measurements for your SJ21 may not be identical to mine, so keep your critical thinking hat perched jauntily on your head.  Measure twice; cut once.  As always, cutting, shaping, sanding, glue solvents, etc. are potentially dangerous to your health and safety - Protect yourself. 
The original hatch was designed as a “box lid” that fits over the lip of the hatch opening.  The replacement hatch is a flat panel of acrylic cut to fit the outline of the "home plate" opening in the deck, resting on top of the lip.  Note the mounting block for the new hinge arrangement.
I elected to mount a Nicro Minivent 1000 Solar Vent in the hatch for ventilation.  This solar-powered fan actively moves 700 cubic feet of air an hour when the sun shines (even when overcast!), and passively ventilates when the wind blows over the top of the vent. The vent is baffled to keep out rainwater, and a damper can be closed to keep out green water.  Before mounting the new hatch, I installed the vent in a 3-1/2 “ hole ( I  know – it says 3-3/4” on the website), centered on the hatch, bedded in 3M 4200 sealant / adhesive.  
Note: the acrylic cuts beautifully, peeling away in delicate shavings, until the blade / drill exits the opposite side. Sharp tools are a must, or your new hatch may shatter or crack when the tool catches and is violently pulled through the material. 

Also – the 3M 4200 goop is sticky stuff, and unless you have elfin dexterity, you are going to smear some on the acrylic as you go along.  Get a bottle of anhydrous rubbing alcohol (approx 97% alcohol) at the drug store – it cleans up the residue after a paper towel clean up. I have broken down the installation into discreet “steps”, but it all goes together simultaneously, as a system. 
Gasket Installation
The hatch kit comes with a length of bulk gasket material, but you will need to mount it to the underside of the hatch, carefully bending it around the curves WITHOUT STRETCHING. The gasket has a self-stick adhesive on the flat side, but it is recommended that you bond it to contact cement on the hatch. 
(For the purposes of this narrative, INSIDE means toward the center of the hatch, OUTSIDE means away from the center of the hatch)
I “dry-fit” the hatch on the lip, adjusting it until I was happy with its symmetry and placement.  Using a felt-tipped marker (and a light touch), from the below, I traced the inside edge of the hatch lip on the underside of the hatch.  This marks the inside edge of the gasket, and I masked to it with tape, cutting curves in the tape at the corners. The outside edge of the gasket lies precisely ½” outside of the original traced line, and this edge must be masked as well.   
The contact cement is applied to hatch in the ½” space between the two strips of masking tape and allowed to dry (about 15 minutes for the glue I used). Starting in the middle of the aft edge, begin peeling away the non-stick backing from the gasket, and carefully apply the gasket to the dried contact cement.  I left the masking tape in place to aid in placement. Take your time, because contact cement + adhesive = forever.  It bears repeating: Bend the gasket at the corners, do not fold or stretch.
You will have more gasket than you need, so carefully cut for a flush fit with the starting edge. For bonus points and absolute waterproofness, you could bond the cut ends of the gasket with contact cement (I didn’t).
Hinge Mounting Blocks
Because the new hatch lacks an aft vertical surface to mount the hinges, a block is necessary to lift the hinge to the level of the top of the hatch. I had some teak lying about, but Starboard plastic wood might be less conspicuous. Alternatively, you could laminate some marine plywood to the desired thickness.  The aft edge of the hatch lip is only 1” tall, but if you found the right hinge, you could forgo the block, angling the aft plate of the hinge down vertically, and through-bolting the hinge to the lip directly.  Bear in mind that this will add another set of hardware to the inside surface of the already-tight hatch opening.   
I sized the blocks to fit on the pad that held the old hinges, mounting with SS wood screws and bedding in 3M 4200.  The gasket, at the aft edge of the hatch, bears against the hole where the aft screw of the hinge would fit, so I reversed the bolt, capping with an acorn nut. A razor slit on the INSIDE edge of the gasket allowed the bolt to be inserted and the head to be hidden inside the hollow gasket. 
Drill and Fasten Hinges
Unless you mounted a vent like I did, you should not have drilled any holes in your acrylic hatch yet.  Review the note about drilling acrylic, above. Take your time – the hatch is expensive and you don’t want to screw it up.   In the words of Ferenc Mate, that would make you an “Elmer”. I drilled all holes fractionally over-sized and bedded each bolt in 3M 4200 inside the hole for some imagined shock absorption and a  watertight seal.
Before drilling for hatch fasteners, I mounted the teak blocks on the hinge pads. I used 2” SS wood screws (pan head w/ washers) through the old hinge bolt holes, bedding the block with 3M 4200. 
With the blocks securely mounted, I carefully lined up the hatch on the lip, marking hole locations for the hinges. As mentioned, the aft hinge hole (on the hatch) intersected the gasket. Making a cut on the inside edge of the rubber allowed the bolt head to be tucked inside the gasket and the bolt fastened with an acorn nut on top. I used washers and locknuts on the hatch, 1-1/2” wood screws into the block. 
The three hinges in this picture are:  Top – removed from old hatch, Middle - two hole hinge to fit block, Bottom – three hole hinge sourced from Port Gardner Sailboats. It’s a Pacific NW bit of serendipity that all three hinges are from Everett-based Sea Dog Line.  
Mount Latches and Hatch Support
The latches from Port Gardner Sailboats are proper yachty devices, made, again, by Sea Dog.  Each unit consists of the screw latch and a catch (or “stop”). After measuring for lateral placement (I lined them up with the hinges), the critical measurement is placement aft of the inside fore edge of the hatch opening.  The packaging has a handy diagram to aid you:
I put the catch level with the top of the inside lip of the hatch, which dictated the following placement:
In the crude cave drawing above, the front of the hatch is to the right, and the right edge of the hatch is on top. This measurement factors in the thickness of the gasket spacing the hatch panel above the lip.  Again, this is for my ’74 MI -Your mileage may vary. 
I recycled the original spring support (with new SS mounting screws – the best fit was an obscure size – good luck). I eyeballed a good angle for the open hatch and spaced the attachment to the hatch so that the spring would not fold upon itself. It works perfectly.
More images: Click Here
The extra light in the cabin is a welcome feature of the translucent hatch, and it looks quite shipshape.  Enjoy!