Sunday, November 23, 2008

Glassing the Inner Skin

Oh boy, this was a fun job. Seriously!

On Monday, we completed a hand lamination of the inner skin, complete with reinforcements around the beam bulkheads and the bagged the entire half of the ama. I am quite pleased with the result and feel like having a party to celebrate. Mai tais anyone?

For all time intensive laminations, I am using Proset 125/229 epoxy, which is produced by Gougeon Brothers (makers of WEST epoxy). This resin/hardener combination has a very low viscosity (450 cps mixed) and makes wetting out the fiberglass easier. The greatest part about this epoxy is its incredibly long pot life (77 min at 72F) and working time (thin film) of 2-3 hours. It might sound strange, but I also find the smell of the 125 resin quite pleasant.

Anyway, in order to vacuum bag the entire hull half, I needed to create a flange to bed the mastic sealant tape and run the excess fiberglass, peel ply, release and breather onto. I left the keel foam proud about 2" above the keel batten and pre-glassed one layer of the deck flange 2" wider than need be before the bagging operation. In addition, I added excess foam at the bow and transom to define the bagging flange there. The entire outline for the mastic sealing tape was defined by a putty mixture to seal the foam and deck flange, in addition to providing a solid bonding surface for the mastic tape.

I cut all the dry fabric (fiberglass, peel ply, release material and breather) to shape before laminating and I left the fiberglass on the foam to be wet out. I did not pre-wet the foam, or, in Ian's building terms, I used the "Dry Method" to laminate the fiberglass. This worked out well - the epoxy has low enough viscosity to wet out the glass and the foam (I checked by lifting up the wet fiberglass) and the vacuum bag pushes the glass tight to the foam.

The results of vacuum bagging are terrific. In my opinion, there is just no way to attain vacuum bagging results with an open or hand lamination process.

Time to Make the Bulkheads

So it's been quite a while since my last post for two main reasons: one is that I had to wait for the fiberglass, vacuum bagging and filler shipment from Fiberglass Supply to come across the Pacific Ocean and two is that I have been working hard and not writing much.

Anyway, the bulkheads are now complete. I made them out of 12mm Corecell foam with single skins of 12oz BD (0/90) fiberglass on the transom, center and bow bulkheads and double skins on both the forward and aft beam bulkheads.

I did the bagging on a waxed sheet of 3/4" Melamine, which has a beautifully finished surface. The laminate schedule for each bulkhead was (from Melamine up) peel ply, skin (or two) of fiberglass, perforated Corecell (with holes 3 to 4 inches apart), skin (or two) of fiberglass, peel ply, release material (with holes 3 to 4 inches apart), bleeder/breather material and the vacuum bag plastic itself. I would recommend a vacuum pressure between 15 to 20 in Hg for these flat panels.

Some suggestions for other builders:

  1. Make sure none of the material (other than the first layer of peel ply) comes in contact with the waxed surface as contamination will certainly cause delamination.

  2. Wet out the bottom skin(s) of fiberglass on top of the foam (which is resting on the peel ply) and then flip them over onto the peel ply on the table. Then put the top skin(s) on the foam and wet them out. It is quite helpful to coat the foam with resin prior to applying the fiberglass.

  3. Cut the bulkheads to shape _after_ laminating them. It is a lot more work to deal with trimming excess fiberglass from pre-cut bulkheads than to just do the initial cut from a flat laminated panel. In short: glass and bag rectangular panels, then cut to shape with the full size patterns. The aft beam bulkhead is particularly nasty if it is pre-cut.

  4. Happy bagging!