Outfitting the tandem kayak, Part 7: Making the hatch rims

Now, I move on to what is probably the hardest (or at least the messiest and most time-consuming) part of this project: making the hatch rims.  The hatch openings will be sealed with neoprene covers, so the rims will be just like cockpit coamings.

The first step is to glue pieces of plastic tubing around the perimeter of each cockpit opening; these will serve as a "mold" over which I can form the coamings.  Like the Rubbermaid garbage can, the plastic tubing will not bond with epoxy resin, so I'll be able to pull it away once a couple of layers of the coaming have hardened.  I use a hot glue gun to glue the tubing to the deck; later, when I remove the tubing, I can peel off the glue.  (I got the idea to make the hatch rims this way while reading Bill Kirby's boatbuilding project, here.)



As for the coaming material itself, my first thought was to use fiberglass and Kevlar seam tape, but fortunately I sought Davey Hearn's advice before going through with that idea.  Seam tape is difficult to persuade into the shape of the rim, Davey said, because of the way its fibers are oriented: the warp fibers run in alignment with the rim, while the weft fibers are orthogonal to the rim's curve.  Davey went on to say that Kevlar is not a good material for a cockpit rim because it fuzzes along the trimmed edge and wears on the neoprene sprayskirt or hatch cover.  He recommended making the hatch rims from ordinary fiberglass cloth cut along the bias.

Cutting fabric along the bias is a trick that's little-known outside the fashion industry.  Designers of ladies' fashions often use bias-cut fabric because it conforms better to the curves of a woman's body.  "Cutting along the bias" simply means cutting the fabric at a 45-degree angle to the warp and weft fibers, as shown at right.  Fiberglass fabric that has been cut this way will "lie down" better on unusual surfaces like a cockpit or hatch rim.  Many years ago I read something about using bias-cut fabric for tight curves and other unusual shapes, but I never really understood it before now.  If patching a boat is a topic of FRP 101 in prestigious universities, then the clever manipulation of fibers is the stuff of FRP 235 or something like that.

Here's the stern hatch rim with a layer of fiberglass applied with epoxy resin.  Building the rims is a tedious process that involves laying on several fragments of cloth, letting the resin harden, trimming/scraping/sanding off the jagged edges of the hardened laminate, laying on some more cloth, letting that harden, and so on.  The tight-radiused corners of the hatch openings require me to reposition the plastic tubing several times.

Here's one instance where I have repositioned the tubing at a corner, using both spring clamps and glue to keep it in place.  Note that I have cut away a previously laid-up section of coaming because I wasn't happy with how it looked.

Once enough glass is in place to hold the desired form, I yank out the plastic tubing.

Here's the stern hatch once its rim is finished except for some final trimming and cleaning up.

Here's the nearly-finished rim for the bow hatch.  This blog post doesn't really convey just how messy and tedious this job has been.  I'm ready to move on to the next thing.