"Richard Casady" wrote:


The very best plastic may be stronger. I think if Boeing is using it
that says something.
Be interesting to see a table comparing the S/N for various materials.
I know the latest fiberglass [and other plastic] is a lot better than
it used to be.
Been my experience that the older fiberglass boats are heavier than a
comparable aluminum boat.
snip

Most existing "fiberglass" boats are polyester resin with woven roving and
mat.

Woven roving is coarse compared to knitted material and requires the mat to
retain the polyester resin.

About the best glass/resin ratio you can expect is 35%Glass/65%resin which
produces a heavy laminate.

Polyester is also more brittle than epoxy resin.

Polyester is also NOT an adhesive which is why you see holes thru the
plywood used for bulkheads with the glass going thru the hole. It provided a
mechanical means of bonding.

OTOH, epoxy is an adhesive, can take advantage of knitted glass which means
much higher glass content with less resin required.

A 50%glass/50%resin ratio is easy to obtain with hand layup techniques,
vacuum bagging can achieve even higher glass/resin ratios.

The result is a much lighter as well as stronger laminate.

Add Airex foam as a core material to the mix and it is a whole new ball
game.

You could build a dynamite hull for a 15'-20' boat using 1/2" thick Airex
foam core(6.3lbs/ft^3), and 3 layers of 17OZ double bias(+/-45degree) glass.

Translation:

3 layers of 17 Oz with a 50/50 G\R ratio= (17*3)*2=102 Oz for each laminate
skin or 204 Oz/sq yard for both skins.

The Airex: (1/2)(6.3*16*36*36)/1728 = 14.2 Oz/sq yard for 1/2" Airex.

204 + 14.2 = 216 Oz/Sq Yard = 216/9 = 24.0 Oz/Sq Ft = 1.5 Lbs/Sq ft.

Pick a metal, you will need at least 1/4" plate to provide equalivant
strength which means a lot more weight.

BTW, add a layer of 17OZ glass, say 6"-8" wide along the keelson for a wear
strip, and you are good to go.

The only problem with epoxy is that it has no UV resistance so a coat of
paint is required.

Lew