Building Logs

Mast Bases Glassed

Posted by Paul

Having de-cored the balsa around the mast (the mast is 200mm across and the ply base is 400mm across) I cut the ply pads to size and glued them into the spaces. I decided on gluing them then sanding back rather than glue and glass wet on wet. There is a small 1mm ridge between the height of the ply and the height of the deck around it. So letting the glue set then grinding it back down makes that difference negligible but trying to ensure no bubble under the glass by wet glue/filler is not as easy. And this glass is a load dissipater so bubbles that weaken it are too big a risk. And you have enough work to do in a big wet out without having to worry about any other issues.

So during the week (Tuesday night) I glued the ply pads in and put another layer of glass over the areas in the underside glass that were broken through (they were joins that had not been glassed and they should have been so sooner or later I needed to do that anyway). Then on Thursday night I sanded them down, nice and smooth transitions, and I also extended the bare glass by removing the bog on the side and foredecks ready for the glass. And Friday night I cut the glass to shape and size ready to wet out the next day.

The plans call for 4 layers of 450g of glass, the largest of them on the bottom is 125mm forward from the middle of the mast and 110mm aft from the middle. And 750mm wide from the centre either side of the post. Then each layer is 100mm shorter all around than the one below it. I don’t have any of the 450g cloth left of I used 600mm cloth figuring there is no harm being stronger than it should be. I toyed with the idea of only laying 3 layers because 3 layers of 600 is the same as 4 layers of 450 but erred on the side of safety.

As I did with the mast base glass on the cabin soles I rolled the bottom 2 glass sheets up together and gradually unrolled them as I wet out with a brush under them on the substrate and onto the top of the glass so at one point I had 2 layers of glass wet out on the deck and the other half of them still dry. Being large areas of glass you either construct some way to suspend yourself over the glass to wet it out or you figure out some way to reach across it. I don’t like standing on wet glass because disturbing the cleanly laid down glass can result in air bubbles or areas not adhered properly to the substrate, not to mention getting glue all over the place or you come up with some method of getting it all down without either standing on it or being suspended over it. The 2 smaller upper layers can be reached across so that you can wet them out one at a time with only the occasional stepping on the edge, no harm done.

port mast base glassedstarboard mast base glassedport mast base boggedstarboard mast base bogged

The wet out took about 4 hours, I started at 8am anticipating it would be a long day and a big job, but in the end it was a lot easier than I thought it was going to be. I have lost count of the number of times I have said that about a looming job only to breeze through. I had a break for lunch while the resin tacked off a bit and then spread a thin layer of bog over the wet resin to get a chemical bond. The glass would need sanding with or without bog, and if it would then be bogged and sanded again I figure it just removes one of the sanding efforts and also removes the risk of sanding through the glass accidently. The bog acts as a warning, when it is gone, stop sanding, but with no bog as a guide it is possible to sand too far and through a layer.

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