Friday, 28 March 2014

Progress on Coamings

John Brooks, SS designer, did warn that the coamings are the most difficult part pf the boat.  He's right! John has issued further detailed instructions on how to make the coamings.  The process is to first laminate the two halves to each other, but not glued to the boat.  Then remove, and lay and epoxy on the dynel cloth onto the deck.  Once set, the finished coamings are attached.

On my previous post you can see how I grafted some additional material to the end of one side of the board. The glue up on the plank turned out fine, although had I planed the board before glue up I might have been able to match up the pattern better.  As it happened while I grafted on a piece from the same end the board, it did cross over a very attractive grain pattern.  Nonetheless, the joint was clean and tight and I think it looks just fine.

I then ran the board through my thicknesser before resawing.  Although I needed 4 x 1/4" thick boards from the board which measured 2"+, it's still a challenge to resaw this accurately.  First I resawed into half  - which went reasonably well but even the smallest wavering of the bandsaw blade eats into your usable stock.  I then thicknessed again before final resawing into the 1/4" boards.  As it happened I ended up with slightly different board widths but the sum of the parts equaled the required 1/2".

The final thicknessing was done with both 1/4" boards held together so that I was able to accurately thickness down to the 1/2" dimension.  Lots of noise, dust and helping hands from my wife and daughter!
The following day, Brian and I attempted to bend the boards into place.  
It went reasonably well until crack! - one board developed a slight crack where it meets the deck.  JohnC who is also building a Somes Sound did warn me about this and suggested using a layer of glass cloth epoxied in between the laminates.  So we planed back the inside of the laminates for about 5" either side of the stress point and epoxied a light glass cloth into the planed area.  Once sanded it was completely flush with the rest of the board and made for a strong and flexible solution.

You can see in this next photo the board with the glass epoxied into it where it meets up with the foredeck - an obvious stress point.  This is just one laminate - the other half, which also has a glass cloth insert, will cover this entirely.

We had to make up several clamp extensions, as none of my F-Clamps reached more than 6" and the coaming needs clamping in areas wider than this.  They are crude but effective - just two lengths of timber separated by a block and wired together, over which a regular clamp is used to apply pressure through the clamp extension legs. We ct a 15deg bevel on one side of the leg, which ensures that the coaming was evenly clamped to the side deck filler.

Once we had one half reasonably fitting, we cut down the edges to size using a batten to create fair lines.  This reduced the width of the board making it easier to bend.  The epoxied glass cloth worked really well and no sign of crack appearing at the stressed areas.   We then cut out the second laminate from the first board, making sure to continue the bevels at the transoms and foredeck - the two halves are not identical.

The glue up went smoothly and the subsequent fitting was easier than when the boards were dry as the epoxy operates as a lubricant initially before it starts to kick.

Here you can see Brian admiring the motley collections of clamps!

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