Whenever I run across a detailed build website, I read it and I have a couple bookmarked for Wood Ducks.  This is a pretty good one and I've attached his section with the coaming:

http://morocz.com/BoatBuilding/DuckBuild7.htm

...and another:

http://thekayakproject.webs.com/page7.htm

Hi,

I just did the coaming on my Shearwater 14 last week (similar boat design/construction, just skinnier).  From what I've seen, there are two methods that both have pros and cons:

1.  Put a piece of plastic on the deck so the coaming doesn't stick to the deck.  Stack up coaming risers and coaming rim with thickened epoxy between all layers.  Clamp (you need clamps at least every 4 inches), but be careful not to over-clamp and squeeze out all the glue.  Clean up any glue from the inside, make a fillet on the outside under the rim.  Let cure.  Remove from boat.  Sand and shape.  Then attach to boat.  The advantage is you can sand the coaming when it's off the boat so it's easier to get underneath coaming rim.  Howerver, it's more steps, and you really can't shape the inside of the coaming until it's on the boat.

2.  Just go for it (this is the method I chose and it worked fine).  I did a dry fit with clamps first to see how everything lined up.  There were several places where I couldn't get all the layers to line up exactly, but that is OK as long as it's close.  I put  tape down on my deck around the coaming area to protect it.  Butter all layers with thickened epoxy and stack them up.  Clamp.  Clean up any glue that squeezes out on the inside, make a fillet on the top and bottom of the outside of the coaming risers (between risers and rim and between risers and deck).  Clean up any epoxy glue from deck and remove tape.  Let cure.  Shape.  I didn't have any problem sanding under my coaming rim, it was actually pretty easy.  I did have more of an issue getting the various layers on the inside or the coaming opening smooth.  Various builders suggest using a jigsaw, sureform scraper, etc.  I'm not good with power tools, and the sureform I had didn't do much.  Sandpaper was slow.  Then I discovered that the tungsten-bladed paint scraper I loved so much for scraping epoxy drips worked REALLY WELL.  It's the kind with a long handle and a knob on top of the blade part so you can get a good grip (got it online from Home Depot).  After I'd spent half an hour of fiddling with sandpaper I had the whole thing shaped in 10 minutes and then did the final smoothing with sandpaper.  

Good luck with it!  It's wasn't nearly as bad as I thought it would be.  

Kathy

Hey Mike,

I tried both ways and both ways work just fine. Building on the boat takes less time to get everything permanently glued on, but I liked the end results of building it off the boat better. The deck area under the coaming is smoother, the fillet is nicer and the spray skirt seats better.

The coaming's shape is set when you build it up on the plastic. The clamps force it to take the curve of the deck and once the epoxy is cured, it stays that shape, except for some very minor springback. When you clamp it on the second time for the permanent attachment it will easily take the deck's shape again. Click on the picture below to see an enlarged image showing the curve being set.

Kathy, your description of building it on the boat is spot on. The only thing I have to add to it is that the Shinto Rasp also does a good job of shaping the inside edge of the coaming. Your fingers must be smaller than mine. I never was able to sand the underside as well as I wanted to on the boat.

Jeff, thanks for posting the link to my site.

Laszlo

 

That's a great tip. I'll remember that for next time.

Thanks to all -- based on what I read here and elsewhere, I plan to assemble the coaming in place over plastic -- thereby ensuring correct curvature and relative ease in sanding off the boat.

This is fun.