Wednesday, August 22, 2007

Strategy for outer hull laminations

The other day Andrew asked a very good question by email. He asked for my thinking in choosing Aeropoxy light filler when the same company produces a filler with reduced moisture absorption(MVS products) specifically for marine applications. This product is heavier, 7 lbs/gallon vs 4 lbs/gallon for Aeropoxy light.

His question gave me pause to think and I had to respond as follows

I chose Canada Composites as my supplier for my materials on the advice of friends who have been working with advanced composites for years. I originally inquired about the 12 and 18 oz knitted bi-directional cloth that Ian Farrier states as the basic spec. The staff at Canada Composites (particularly one who is a sailboat dinghy designer and builder) talked me into using more advanced materials. We discussed the MVS epoxy resin line but I ended up going for the highest quality product that they supply. Aeropoxy resin states the best high temperature (float interiors can get very hot) and tensile properties. I also liked the fact that the hardeners do not have the harmful stuff and is fairly safe (and not smelly) to use. I thank Aaron at Canada Composites for giving me this alternative.

At that point I accepted the fact that I would be approaching the build a little different than most, ie making the F22 more like an aircraft (light and strong) than a traditional marine approach(heavy and durable).

So, the Aeropoxy light filler is light, and that is why I am using it. As far as moisture absorption is concerned I do not think that the filler will absorb any more moisture than the foam itself. I have a link somewhere from a boat surveyor who is very concerned about moisture absorption.

I do not think I would use Aeropoxy light after the floats hull exteriors are laminated. The MVS product does indeed look like a good product for the final fairing. I obviously want to minimize this work and get the foams as good as I can. I think that my use of the glue rather than the epoxy putty makes preparing the foam even easier.

I also had the thought that the boat will be a trailer tri and will not be sitting in the water for whole sailing season.

I have to admit that as a test and for my own peace of mind, I have also sprayed some water on the filler and the exposed foam. To my mind the filler dried quicker.

I'm also thinking that I have spent so much time thinking about hull interiors and structural issues that I had not thought through how to best proceed on the outer hull and below waterline parts.

So here is my revised strategy for resin and fairing compounds.
  • For inside laminations (9 oz s-glass) and structural components I will to continue to use Aeropoxy resin.
  • Filling foam in preparation for lamination I will continue to use Aeropoxy light.
  • Outer hull laminations and fairing I will use MVS resin and fairing compounds.
  • I will continue to plan to vacuum bag the outer hull laminations to ensure good adhesion properties.
Thanks again for the timely question Andrew.

No comments: