Friday, June 02, 2006

Coaming lip, sanding, hatches cut and hatch lips built

-----I have photos to add but they'll have to wait until a later date--------

I have gotten a few things done in the last couple of weeks. The first on my "to do" list was to build the cockpit coaming lip, the rim around the top of the cockpit to which the skirt attaches. There are a number of ways to do this. Probably the most common way it is done on strip-built kayaks is as described in Nick Schade's book using 1/4" wide by ~1/8" thick strips of hardwood (ash or walnut are common), wrapped around the top of the coaming with about 6 laminations glued in place. While this is reported to be easy enough, dealing with many thin pieces of wood buttered in epoxy (they get darned slippery) and trying to keep everything aligned didn't have all that much appeal for me. Since the finished product is 1/4" thick by 1/2"-3/4" wide hardwood & glue, it seems to me that this might be heavier than other options. A second common method is that described by Vaclav on the One Ocean website, where a coaming is laid up in carbon fiber (and/or fiberglass, but carbon seems to be common) over top of a form built on the boat out of styrofoam. This method seems simple enough, but I don't have carbon fiber so quite a few layers of glass would likely be necessary to get the required strength and stiffness. Something I began to think about was using thin (1/8") birch plywood reinforced with a couple of layers of fiberglass to form the lip. The birch plywood is thin enough to flex into place and conform to the curvature of the top of the coaming (it is curved from the side profile), but when encased on both sides in layers of glass, should be both stiff and strong. Recently, I saw a post on the KBBB where a builder (Gaetan) used plywood (stained to match the colour of the boat) for his coaming lip. The result looked great and that sealed it - that's how it was going to be done.

The process was fairly simple - I rough cut a piece of 1/8" birch plywood to the size of the cockpit rim, leaving it over-sized to be trimmed later. I oriented the grain perpendicular to the boat so that it flexed into place easily. I then tacked the lip into place on top of the trimmed coaming riser using CA glue (I should have been using accelerator too but the spray pump on the little bottle is buggered and I've given up fighting with it). I then trimmed the inside of the cockpit lip to be flush with the riser and rounded off the corner a bit. I then glassed the lip with 2 layers of bias-cut 4 ounce fiberglass which wrapped from the top of the lip, down the riser, and onto the underside of the deck (barely). The 4 ounce cloth had no trouble making the bends and wets out very easily. It is very nice stuff to work with. Once this had cured, the rough edges at the bottom were smoothed out (a scraper works very well as long as the epoxy is not too hard) and the outer edge of the lip was trimmed down to it's final size of 3/4". I then applied a fillet of epoxy underneath the lip at the junction with the riser to smooth out this corner to a radius the glass can manage, then applied 2 layers of fiberglass which again wrapped from the deck, up the riser and under the the lip. I used a trick I read about on the KBBB to hold this glass in place and make things in this hard to work area "smooth as glass" (described by John Monroe and credited to Rob Macks). I used 3/4" flexible vinyl tubing (purchased at Cdn Tire) squashed in underneath the coaming lip and held in place with spring clamps. Once the glass had partially cured, the tubing was pulled out to reveal ---- a mess! It seems I didn't get the tubing in far enough in many places and there were a lot of voids and air pockets above the glass and underneath the glass. I scraped some of the rough edges I could reach, but there is still a lot of smoothing to go underneath the lip. I may try to put another layer of glass in under the lip since I'm sanding a lot of the strength away in order to clean up the mess. For now, it's not easily seen so it's something I'm working on here and there while focusing on other things. In the end, the plywood coaming lip worked really well and was very easy to do, but I need to work on my technique for glassing underneath. One thing I considered was to put a layer of glass on the underside of the whole lip BEFORE tacking it in place on top of the riser while the glass was still green and flexible. This would have been very easy, but I went for what I thought would be the stronger method by having the glass continuous from deck to riser to lip. Next time, I'd probably do it as I originally considered with putting a layer of glass on the underside of the plywood lip prior to tacking it in place, with a fillet underneath and an extra layer of glass on the outside, avoiding all the trouble of trying to work with glass underneath the installed coaming lip.

While the weather was nice last weekend (overcast but comfortable working temperature) I took the opportunity to drag the boat outside to do some sanding in the fresh air. I also took a few pictures, and sat in the boat to determine the approximate location of the front bulkhead (to ensure I cut my hatch in front of it!).

This week, I cut out the hatches. This went fairly well despite my nervousness about cutting giant holes in the deck of boat. The first step was to determine the shape of the hatches. Using the offset's in Nick's book as a guide, I experimented with a number of shapes. I printed these out on the computer to the right scale which meant taping together a bunch of sheets of paper to create my templates. After considering the diamond shape provided in the book and different egg shapes, I settled on a trapezoid shape with round corners and sides roughly parallel to the sheer line. I then masked off the areas to be cut and with my templates transferred to pieces of cardboard, I traced the shapes onto the boat. Looking at things on the boat, I decided that I had the rear hatch too large, so I scaled it down a bit (about 1/2" all around seemed about right) and moved it aft about 6". This all took me the better part of an evening to get something I was satisfied with.

I started the cut as others have described, using a cutting disc on my dremel. I then used a blade from the jig saw and by hand cut through to make the slot wide enough to fit the jigsaw blade. Then with a new Bosch fine-cut blade and the jig saw on a medium speed, I cut out each hatch. The actual cutting went fairly well. I am glad that I decided not to rush out and purchase a new $200 Bosch jigsaw, and I am glad that I did decide to spend the big bucks and get the Bosh blades (about $12 for a pack of 4). In the end the actual cutting was a bit anticlimactic (which is OK, that means it went well).

With the hatches cut, it was then time to build the hatch lips. I used the method described by Vaclav on the One Ocean web site. Ken (aka Spidey) has some good pictures and a good description of the process on his web site. Before heading to the hardware store I should have double checked what size of weatherstripping to use to form the gasket channel, but I didn't so I just got what looked about right. The 1/8" stuff looked too small, so I went with 1/4" x 3/8" closed cell foam gasket tape. I taped the hatches into position from the outside, adding a couple of strips of cedar to ensure the hatches would sit flush despite any pressure that would be applied in laying up the glass for the lip (not to mention the 20 lbs of wet sand I piled on top). With the deck turned underside-up, I used thin clear packing tape over the whole area to ensure that my gaskets would not yet be a permanent part of the boat. I then applied the self-adhesive weather-stripping to the perimeter of the hatch lid staying about an 1/8" in from the edge. With this in place, I applied a fillet of thickened epoxy (406 filler) pigmented black with graphite powder (mostly because everybody else seems to tint their hatch lips and I didn't want to be left out) on both sides of the weatherstripping. I then began to lay up strips of glass over top of this to make the hatch lip. For the first 1-2 layers, I used 4 ounce glass because it conforms better to curves and does not trap air as easily (I think I still trapped a fair number of bubbles), then followed with strips of 6 ounce glass cloth for a total of 5-6 layers. The glass was wet-out 1 layer at a time using epoxy with graphite powder added to make it black-ish. Once all of the glass cloth was layed up and wet-out, I put a sheet of poly over top and piled damp sand on top of that in an effort to push everything smooth. I was somewhat surprised how long this process took. I started at 10 pm, and did not complete the process until 1:30 am. In the morning, with the epoxy partially cured but still flexible, I removed the sand and the sheet of poly, then peeled the gaskets off of the deck and removed the tape. It all went pretty well, though there are wrinkles from the plastic layed over top. Next, I will trim down the rough edges of the hatch lip, scrape out the weather stripping from the gasket channel, then permanently bond the hatch lip to the underside of the deck.