home build - mast and gaff - questions

[Clinton1]

Hey all,

I need to build a small mast (4meters) and a gaff (well, 2 gaffs - one is a replacement for a 'lost' one from a Heron).

First time I've done this.

I'll do a hollow birdsmouth join mast and gaff... my workspace is long enough and I'm not worried about the difficulty of it vs laminating up solid timber and then rounding it. (I've discounted the solid section mast and gaff as getting the timber for that is pricey).

My question is:
Is there any benefit to using a thinned epoxy coat, then high strength filler powder mix epoxy in the internal corners of the birdsmouth over plain epoxy?

I'm aware of the clamping requirements, the need to maintain correct spacing and to chamfer the internal edges of the join to allow a fillet of filleting mix epoxy to lay in there... may need to put in a plain epoxy run over some faces as well. Its a waste of time in my opinion... but what do I know???

Anyone have any thoughts on this... my opinion is that you would create a potential failure line due to the very strong fillet tearing from the timber. ???

Apologies in advance, I'll be off line due to work till the coming weekend.

[PAR]

First off, don't thin the epoxy. In fact, you shouldn't ever need to thin epoxy. If you want to lower the viscosity then warm the work and/or epoxy. Thinning epoxy just dilutes it and just a small amount of dilution will make a huge difference in the strength and physical properties of the cured goo. So, unless you have a strong chemical understanding of what happens with specific dilutants, then don't even think about.

The epoxy steps on a birdsmouth mast are; coat all the internal areas of the mast with three coats of straight epoxy (no thinning, no fillers), using the wet on green technique (wait until the previous coat is just barely tacky before the next). Once three coats of neat epoxy are on and it's at the "green" stage, apply thickened epoxy to the notches that will receive it's neighboring stave. Align and clamp (not too much pressure, just enough to insure adhesive contact only). I use plastic wrap, strips of rubber, bits of line, what ever is handy. Once the inside has cured, remove the clamps and begin whittling it down to a round spar. When it's round, fill any gaps in the staves with thickened epoxy. Lastly apply 3 straight epoxy coats to the exterior of the mast.

3 coats seems excessive, but it insures two basic fundamentals, the first is that it has sufficient film thickness to prevent moisture from getting to the wood and second that this hard, plastic resin has encapsulated every square inch of surface, inside and out. This makes it no long a breathing piece of wood, but a dimensionally stable bunch of wood with a hard plastic shell.

As far as a fillet reserve area, forget about it. You're making more work for yourself. Unless this is a very dainty racing mast, who's life expectancy may only be a few races and the strength edge, verses light weight is a very carefully strung tight rope, then it's not worth bothering with. I've made mast that had 15% and less wall thicknesses. They didn't last long, but they won races because they were a few percent lighter then the competition.