Wednesday, March 18, 2009

S&G Night Heron – Fibreglassing the Outside

Quick notes from here on as the exterior was considerably easier than the interior.

I bias cut the fibrglass for the exterior to get it to drape better. The epoxy application was much simpler than inside although I did find a few areas that ended up a bit on the dry side. Main reason for this was I ended up working into the evenings and the lighting was awful. This also resulted in a couple of unnecessary floating bubbles and drips – but all easily fixed. So much easier after having done the interior first.

One tip (I think) was to fibreglass across the sheer line; that is, when I fibreglassed the deck, I went to about an inch beyond the deck-hull join, and likewise when I fibreglassed the hull, so that the join between deck and hull was secured with interior tape and a doubling of the exterior glass.

I doubled the glass on the exterior hull from the sheer line to the keel so that under my body I ended up with 4 layers of 200g (6oz) fibreglass.

Having read about the difficulties of making a lightweight boat I spent a lot of time checking the weight as I progressed. One very useful thing here (especially to avoid wastage) was a cheap digital scale. I bought this from a supermarket for $16 and used it to successfully mix epoxy down to 1g hardener and 5g epoxy. I recorded the weight of each batch of epoxy and I weighed the boat after each major application so I could clearly see the increase from 12kg prior to exterior glassing to 19kg after the fill coats were complete.

I found the fill coats a little painful. I seemed to never quite get the right amount on. I’d put a coat on, sand some off, then try again; many times over. What was particularly irritating here was that to avoid excessive exposure to the epoxy while curing I would make myself wait a few days before any sanding. The time just seemed to drag!

If I was doing it again I’d make two changes.

Firstly, I’d use a slow hardener and warm epoxy/conditions. I found that on a few of my (autumn) evenings the temperature had dropped to maybe 15C and the epoxy had thickened and would spread easily. You want it to spread really easily so a really hot day with a slow hardener would be a better combination.

Secondly, I’d use a random orbital sander more extensively. I spent far too much time continuing on with hand sanding when I should have just used the ROS. The pads clog up quick but crikey it does a hell of a job!

1 comment:

james said...

Thank you so much for this. I'm just about to get the CLC kit for this craft, and it's my first time building anything more complex than a sawhorse, and being able to watch you go through it both helps me anticipate some of the problems and really gives me the confidence to go for it. She's beautiful. Thank you. :)

-- James