Super Flexible Material

Submitted by JimD777 on Fri, 02/21/2020 - 10:15

I'm going to build a molded fiberglass cockpit rim. I've done it before, but I forgot where I got this very bendable material:

Is there any other type of material besides plywood that might work?rim


Sat, 02/22/2020 - 19:04

I did a fiberglass coaming on one kayak. Measure your coaming length. I used a 8 ft 2x4 on saw horses for a table. Cover it with wax paper. I used 3" 9 oz fiberglass tape and wet out a length on the table with blackened epoxy and then added a 2nd layer of the 9 oz tape on top of that. Offset the 2nd piece so the finished edges don't stack up. The next day you will have a stiff but highly flexible piece of fiberglass. I bend it into the cockpit opening and epoxy it in there with hardware store 15 min. epoxy. If you coat the opening and the substrate, in several minutes as it kicks it will become highly tacky and you can press it right into position. Later you add a filet and glass the outside to the deck and the inside running glass under the deck. Work with the kayak upside down. I added a bend wood coaming lip. A Black coaming with a wood lip looks great. Of course, you trim it off top and bottom etc. Also, you can overlap the joint of the coaming or try for a butt joint which is harder to calculate. If you do the overlap, taper the substrate on the bottom.


Sat, 02/22/2020 - 20:55


Nice to see some signs of life here!


I looked in my files here and I don't have pics of the process, but it's not difficult. Just make sure you keep things lined up to a centerline reference as you go.

Make cardboard templates of the cockpit opening and the coaming perimeter - for a keyhole cockpit these will be quite different.

Decide how much  (or little) space you want between the deck and the coaming lip. I make this bigger than necessary to make sure I can easily get any sprayskirt on the boat. Sometimes in a quick launch or re-entry, it's nice to be able to get the skirt on fast. That space will be the thickness of the pink insulation board you need.

Use the templates to cut the insulation board, but make the mold wider than the finished coaming - you can trim the coaming to size later - easier than trying to add material.

You can use a roundover router bit (carefully) in a router table to form the rounded inside edge of the coaming. Sand down the deck to meet the foam mold evenly. I generally glue the foam to the deck with epoxy and microlight filler (easier to sand smooth later), using spring clamps with cardboard pressure pads to avoid denting the foam. Once the foam is attached to the deck, sand it smooth.

Laminate strips of glass cloth (and carbon?) over the mold, wrapping them under the deck by hand. It's messy - protect the hull inside with paper to avoid drips. Finish with glass over the carbon- it will give you a bit of protection against sanding into the carbon. Once the epoxy cures, sand any lumps and overlaps smooth. I usually put a few coats of epoxy (low colour like S3 Silvertip) over the coaming to give it some depth.

Remove the foam with a wire wheel in an electric drill and by hand with a wire brush and get the last traces with acetone.

Trim the outside of the rim with a diamond wheel in a Dremel, and sand smooth

Fine sand to 320 or 400 grit and add clearcoat.

Turn the boat over, sit on the floor and lean up the inside.


Other methods are described on Bjorn Thomasson's site; try:



Sun, 02/23/2020 - 12:08

Jay's method is a slick way to make a glass coamng riser, adding the 'top' -lip- later.

I like to make coamings really strong, with a thin lip/edge. Strong because the coaming is one place that people usually grab to flip boats or hold boats upright during rescue (practice, hopefully..). Thin because sprayskirts grab better on thin coamings. I see this often - a sprayskirt that works fine on a glass (factory) boat will slip off a poly boat with a thick coaming. 


Sun, 02/23/2020 - 12:11

That coaming pic of the yellow Frej shows the coaming before the final sanding and epoxy top coats, and before trimming to final width.


The glass/carbon stays flexible for a few days, so it's possible to 'bend' the coaming lip down toward the deck with spring clamps and long pressure pads during that period.


Sun, 02/23/2020 - 22:37


After the sacrificial foam mold is glued to the deck, there will still be a sharp transition at the inner edge between the coaming mold and the wood-core deck of the boat.

I like to have a smooth transition between the coaming and the inside of the boat, so I sand that transition area - basically feathering the underside of the deck to make a smooth transition to the glass coaming. The glass should wrap around smoothly to the underside of the deck, when you hand-laminate it in place.



Sat, 02/29/2020 - 07:42

If you're looking for a thin flexible material as your photo shows, you can try formica or other brands. If you know or ask someone who does kitchens, you might find scraps. Everyone is nuts these days with having stone counter tops but its a thought. Formica is less popular but its around.