"Knot Likely" -- Carbon Fiber Cockpit Coaming

Click on the photos for a larger, uncropped version

The cockpit coaming was formed before the deck was removed for sanding and glassing on the inside, but it seemed more appropriate to me to create a page specific to building the cockpit coaming and thigh braces. Once again, I'm using a modification of the technique developed by Vaclav Stejskal of One Ocean Kayaks. This time I started by laying up florist foam around the coaming riser.

After hot gluing foam blocks around the riser, (see below for more about this!) I sanded the foam to the shape desired for the coaming rim. I like to have the outer edges droop down a bit - this is easy to do with the sanding block and foam. I've talked to others who fabricate their coamings in a similar manner. The materials used for the form vary widely! I use the florist foam because it's cheap and easy to sand.

After covering all of the mold with masking tape, I added a layer of shiney duct tape to serve as the parting surface. Last time I sprayed the masking tape with 3m cement and then glued Saran Wrap to it for a parting surface, but it tended to stick to the coaming. I reasoned that the slick surface of the grey tape might work better. Always willing to try...

The coaming was laid up with 9 layers of material. The first two (bottom) were 6 oz. bias cut glass. The next 5 layers were alternate layers of bias cut 5 oz. carbon fiber with 6 oz. glass interspersed. The top two layers are 6 oz. glass. The key is using cloth cut as close to 45 degrees as possible since it shapes to the compound curves easily. I made it a point to save my two longest pieces of carbon fiber for the top layer of CF. You can spot the overlaps in the CF layer, and I didn't want to make it with a number of noticeable joints.

I removed the coaming from the form the next morning. As usual, it took a bit of persuasion, but came out fairly easily after inserting wedges under it. The grey tape worked well, but I should have used more to make a wider surface.

I was feeling really proud of myself until I went to remove the foam from around the riser. The hot glue sticks MUCH better to fiberglas than it does to bare wood! I must have spent more than two hours cleaning the glue off of the deck and coaming riser. Next time, I'll mask the deck and riser before gluing the foam in place. On the other hand, some of those wood coaming rings look mighty nice. Maybe I'll have to try one of them.

While I was laying up the coaming, I also molded some material for the thigh braces to be added. Last time I built thigh brace forms from a 2 gallon Rubber Maid pitcher. That proved to be a bit agressive. This time I found a mold with a larger radius! I'll cut both thigh braces out of this piece of material.

Several weeks later, using a piece of the material that was molded over the bucket, I positioned the brace and marked the cut line with an awl. The braces were cut out using a sabre saw with a very fine tooth blade.

The braces were fitted in place, the gap filled with black thickened epoxy, and then three layers of 6 oz. glass were laid up on the under side of the braces, tying them to the deck structure. These pieces extended across the whole surface of the thigh brace and onto the under side of the deck, continuing almost to the shear line.

Once the underside cured, the deck was flipped over, the brace and coaming were masked, a fillet of tinted epoxy was applied to the coaming/brace joint, and then one layer of cloth was applied that went from the inboard edge of the brace, up the side of the coaming, and across the lip of the coaming. If the last boat is any indication, I'm likely going to have to round off the corner a bit more. I like agressive braces, but these may be too large. Won't know for sure until I get the seat carved.