: Either that or you are building a very small boat, and only putting
: your epoxy on one side.

: Since you stated that you would be glassing both inside and outside
: of the boat, then your glassing surfavce area is going to be
: twice that of the surface area of your wood. If your example was
: for 3 square meters of fiberglass cloth, then you would want to
: figure th density of 1.5 square meters of wood. As it is, you
: are figuring 3 square meters of both--so either you are over
: estimating the amount of wood used, or underestimating your
: glass and resin.

: While the "best" mix of glass and resin is roughly an
: equal weight of each, you won't see this on any homebuilt boat.
: Such a mix would leave the weave visible, so we routinely slap
: on one or more fill coats, and just as routinely, we minimize
: their existence in our memories. We also tend to (conveniently?)
: forget that the 3 to 10 layers of varnish we so lovingly apply
: also has a certain weight, so the boat gets lighter everytime we
: talk about it :)

: For a better "quick" estimate of what your boat will
: weigh, go with the measurement of the cloth you bought to cover
: it, and figure half of that as the measure of the surface area
: of your wood. The waste from the cloth should be about the same
: weight as the extra resin and varnish. Going with a slightly
: large figure for the wood's surface area, and consequent volume,
: helps to account for the coaming, back rest, hatch fittings, and
: other such parts. Easiest way to mdify your formula would be to
: insert a "/2" after your wood density, effectively
: making the wood's surface area half of the glass length.

: PGJ

Hmm, in the equation I've got 2*3 square meters for the surface area for the fibreglassing and just the one 3 square meters * the wood density for the contribution of the wood weight. Like you say it's the attachments, coaming, hatches, fill coats, second layers of fibreglass etc etc that all adds up.

It's interesting to just play with the epoxy contribution - you really have to lift it to make the weight go up.