Saturday 2 February 2013

Wood/Epoxy v GRP laminate

I  read someplace that a cubic foot of plywood epoxy weighs 44 pounds and that a cubic foot of glass reinforced laminate (grp) weighs in at 100 pounds!

The truth can only be known if we weigh sections and find out?

This plug of GRP came from Gulliver of Knysna, an Endurance 37 taken off the rocks near Slangkop Lighthouse, near Kommetjie, South Africa. it weighs 30 grams and was measured to be 25mm thick.
With a diameter of 33mm.

Simple to see we have a 30 grams weight here, a similar diameter plywood epoxy plug but only 21mm thick, weighed only 16 grams, the ratios are close, I need to calculate this a little and see just what the ratio between both materials is?

A simple division gave me just short of 59% lighter with the plywood epoxy laminate, weight means money, it aslo means a slower boat.

Note, the boat this plug came out of has since been to  St Helena and Ascension Isles, Brasil,
Trinidad and Tobago, Venezuela and very recently back to St Helena in the 2012 Governors Cup Race!



I have just checked the plywood cores, they are actually 40mm in diameter, so my percentage difference will change upwards, I note they also weigh 14 grams, new calculations later!

The 40mm diameter x 21mm thick hull skin plug is already more than 50% lighter than the GRP plug, so its starting to look like the original 44 pounds to 100 pounds ratio is correct?

More on this when I have run the calculations.
How to fiind the area of a circle?

This needs to be known before I can weigh up one core plug can be matched to the orther as we have a different diameter and also a different diameter!
The area of a circle formula = Pi r squared

See also