Companionway Hatch Replacement

By Todd Schlemmer:

For any endeavor, there is an easy way and a hard way to accomplish your goal.  Luckily, hindsight is 20/20, and the following narrative will hopefully help you avoid some of the difficulties I encountered.  

For this project you will want: 
  • ½” Teak Marine Plywood
  • Stainless Steel wood screws
  • Table saw or Skil saw
  • Hand drill
  • Straight edge(s)
  • Measuring tape
  • (power) sander and sandpaper
  • Waterproof glue (epoxy or other)
  • Teak oil and rags
  • Safety equipment – eye, hearing, and respiratory protection, gloves?

Nice to Have:

  • Hand plane or block plane
  • Angle Finder or Sliding Bevel tool
  • Rasp or Surform tool
  • Framing Square
  • Corrugated cardboard (template material)
WARNING: I am advocating the use of sharp and dangerous tools.  If you do not have the skills and experience to use this equipment, please, please, please find someone possessing the skillset to help you.  I cannot teach you how to use these tools in the context of this article.  You have been warned – be mindful of the risks involved.
Step One – Materials
At the very least, I recommend the use of a marine-grade plywood for this project.  Since you are lavishing your love and energy on this, make it look nice and spring for teak.   A quarter sheet of ½” plywood provides ample material for this project, even allowing for a mistake or two (ask me how I know).  Finding that ¼ sheet of plywood, however, may take some doing.  If you are in the Seattle area, don’t waste your time at West Marine or Fisheries Supply; visit the friendly folks at Home Builder's Center, 1110 W Nickerson St, Seattle, WA 98119  (between W 11th Ave & W 12th Ave).  I paid about $60.00 for the necessary plywood.
Treat your plywood with care during handling and cutting.  Any scratches or gouges you create will drive you nuts when you try for a Bristol finish later.  Not only is your teak plywood expensive, it is a precious natural resource – it’s bad karma to waste treasure. 
Consider the use of Plexiglas or Lexan for one or more of your dropboard(s).  The windows in the San Juan 21 don’t allow much natural light into the cabin, and an additional window in the companionway would increase the available light.  I leave the particulars of procuring, cutting, and finishing these plastics as an exercise for the interested/motivated sailor (I do know that Lexan is very strong, Plexiglas is easier to work). 
If you opt for adding wood cleats to your dropboard(s), I implore you to secure them with screws while the glue dries.  You’ll only need a couple per dropboard, so get stainless.  Good sources for SS fasteners are West Marine, Stoneway Hardware (Seattle), or the big box hardware stores.
Use your favorite (meaning: you have it on hand) waterproof glue.  I had to buy some, so I picked up one of those handy two-part epoxy syringe kits.  They come in a few strengths/drying time specifications – I used the 5 minute variety for ample working life and optimal strength. 
Step Two – Measurement
NOTE: There are few measurements listed in this article, because I suspect that each San Juan 21 is a one-of-a-kind creation, and, as such, they probably vary by a fraction of an inch in any given dimension.  

Easy way – Use your old dropboard(s) as a template for your new one(s). 

Keep in mind any errors in the fabrication of your old dropboard(s) will be perpetuated when you duplicate the prior work.  Place the original dropboard on your plywood; butt a straight edge along an edge. You must move the dropboard out of the way to scribe the outline.  Clamp the straight edge in place and return the dropboard(s) to its original placement on the plywood, against the straight edge.  Repeat for the remaining three sides.  If you are happy with how the old dropboard(s) look/fit, this is vastly simpler than the…
Hard way – Measure the companionway opening and the additional width for the dropboard tracks on each side.

 Done carefully, this will result in a perfect boat-specific fit of which you will be very proud.  This is somewhat fiddly, in that you must measure the angles at the bottom of the companionway.  You can directly measure angles with an Angle Finder (essentially an adjustable protractor), or a Sliding Bevel gauge.  Indirectly, you can measure the widths across the companionway at two heights, a known distance apart.  Assuming symmetry of construction (and I don’t), strike a centerline on some sturdy cardboard (used as a template), and plot the widths perpendicular to that line.  Connect the dots, and you have the measured angles of your companionway opening.  Add the necessary width to fit into the dropboard tracks each side of the companionway (again, measure carefully).  Cut and trial fit.  Trim and trial fit.  Repeat.  I told you: fiddly.

Should you want two or more dropboards, remember that a table/Skil saw kerf is typically 1/8”, and must be factored into your measurements, preferably laying out each dropboard individually.  If you intend to make one big board and cut it into two or more pieces, your template must be taller than the original.  After you make your horizontal cuts, you will need to remove material from the edges of the TOP dropboards, or they will be too wide to fit snugly against the LOWER dropboard.  Removing material from BOTH sides (bonus point!) will best line up the grain.  I made my top dropboard 10” high.
Don’t forget to factor in a bottom lip, below the companionway opening, for better coverage.  I used 1 ½” (one and a half) as my lip measurement (as per the original dropboard), but ½” should be sufficient.  I increased the height of my dropboards to be ¼” taller than the bottom edge of the sliding hatch.  This requires lifting the hatch up and over the top of the dropboard, but results in a better “seal” of the opening.
Step Two and Half – Check Your Measurements
Really.  I know you’re all fired up about this, but slow down.  Have a cup of coffee. Phone your family.  Double check that what you are about to commit to, in your expensive plywood, actually reflects the reality of your boat.  Okay, it’s time to make some sawdust.
Step Three – Cut Out Blanks!
The hardest part of this is cutting the angled sides accurately.  A table saw is invaluable for making square (90 degree) cuts, or cutting on a bevel, but making ANGLED cuts requires either a steady hand and a miter gauge (very difficult with large stock – like a ¼ sheet of plywood), OR some kind of angled guide against a ripping fence.  Knowing the angle you need to cut will aid in making an accurate guide.
It might just be easier to use a Skil saw to free cut the edge (being double-triple careful to cut OUTSIDE the line), and then sand or plane to the line. This is a technique fraught with danger and requiring practice.  Do not practice on your project, and give great consideration to what the blade is doing underneath your work piece. 
After cutting the angles, you will have at least one parallel cut to make your dropboard(s).  The best tool for this job is the ripping fence on the table saw.  Cutting slowly will minimize tearout across the grain, but you will probably want to soften the edges anyway, with a plane and/or sandpaper.  If you are making more than one dropboard, a slight bevel on the matching edges will help keep the liquid sunshine and green water out of the cabin.  I used an angle of 15 degrees, sloping downward, AFT.   
IMPORTANT – Expect that the two sides of your plywood will be different colors, and have an entirely different grain pattern.  IF you are making dropboards that are NOT separated by a saw kerf, keep the ripping fence on the longer side of the blade, adjusting for width.  Set your table saw blade and then make both cuts, ensuring that they are identical. You will need to flip one of the pieces over to make sure that angles meet properly, and that the same side of the board is on the outside.  Consider that, because of the bevel, the sides of the resultant dropboard will have different widths – you may be cutting to a line on the under side of the board.  Take your time, think this through.  (If you screw it up, at least you can always paint it.) 


Step Four – Cut Rabbets


Cutting the notches out of the sides and bottom (known as “rabbets”) is straightforward if you have access to a table saw.  Since all the edges on our dropboards are straight, the rabbets can be cut against the ripping fence, board on edge.  IMPORTANT – Set up the saw such that the waste is AGAINST the fence.  If your board should tip either way (very possible), the blade will cut into the waste and not into the bit you wish to keep.  Also, because the blade is cutting inside the plywood, you can direct pressure against the edge of the plywood (with a suitable “pusher stick”). 


The first cut is critical for depth – the second cut needs only to clear the previous kerf, but is critical for width.  A little time and attention will result in perfectly square rabbets (mine were not – I had to clean them out with a plane).  Utilize some waste plywood to make trial cuts, carefully measuring the results.  Additionally, I planed a bevel on the rabbet (measurements above are nominal) to fine-tune the fit inside the tracks.  Take your time and know what you want to achieve. 
Fit the newly cut dropboards into your companionway.  Note any stickiness and remedy.  You may need to shave material off the edges or bevel/ thin the rabbets.  A hand plane (set to remove thin, thin, thin shavings) is indispensible here.  The table saw may be the best solution if your rabbets are not wide enough.  They fit? Great!
I added a cleat on the bottom dropboard to bear the weight of the dropboard and withstand the force of dropping it into place (not that I would ever treat my work so cavalierly).  Another cleat overlaps the two dropboards, preventing the top board from bowing or sagging down on the bevel, and providing a handle to lift from, inside the boat.  I mixed up some 5 minute epoxy and secured them with SS wood screws while the glue dried. (Wear gloves when working with epoxy – people can develop life-threatening sensitivity to epoxy from repeated exposure.  Sometimes.)  Despite careful centering and pilot holes, they both came out slightly crooked.  Alas, folk art. 

Step Five – Finishing

If you don’t own a power sander, beg, borrow, or, uh… buy one.  I only used a couple of sheets of 440 grit to finish the plywood.  Varnished Teak is divine, but you will be re-varnishing it for the rest of your life. Personally, I relish the look of oiled teak.  In either case, removing the sanding dust is important for a fine finish.  I don’t have much to offer here – I merely wiped it down with a brush and a rag.  You can buy (or make) a “tack cloth” to which dust sticks like glue, essential for a proper varnishing.  I gooped some teak oil on the plywood, rubbed it in, and repeat two more times, allowing 24 hours to dry(ish).  Follow the instructions on your bottle of teak oil, and you won’t go wrong.
Lastly, I bolted the eye for the hasp onto the top dropboard, using SS machine bolts and acorn nuts.  Make your holes just a wee bit large, and you can fettle the alignment of your hasp.  I might add some snap screws to the bottom board to hang a chart case from.  A louvered vent would be a nice addition to the top dropboard, but I think enough air sneaks in and out around the sliding hatch. 

Looks like a Backgammon board.  I intended to get abetter match with the grain, but owing to the learning curve in making angled cuts, I was forced to make the top board from a different part of the plywood.  I lined up the grain as best as I could. 

 This picture deliberately upside-down.  Hey – a gouge! (sigh)

Beauty and the Beast.  The board with the NOOD sticker is FIR marine ply - Serviceable, but rough.