Some Thoughts on Building Low Weight Structures

From the always active mind of Dan Newland …..

Hey guys.

I was using this table when it occurred to me that perhaps you could also use these figures.

Attached are some real, measured weights I’ve kept for when I need to do calculations, (the exception are the foam cores that are calculated).  Many came from laminate samples or real wood pieces that I have and commonly use around the shop.  It occurred to me that maybe you could use this but if not, I will assume the delete button works well and it can go into the Ether.  Anyway, I try and keep the samples and do honest weights when I can since I always am a bit suspicious of some assumed weights.  So these are for the most part real world weights based on parts that I have weighed but of course the wood can go up or down.  Still, it is valuable to have, sorry if it is hard to read.

Two things to point out.  Note that for simple open mold lamination, the weight of 10 oz. glass, style 7500 varied quite a bit.  This was not a mistake and I have checked it a couple of times but the more viscous epoxy resins really adds a lot of weight so for open molds, it is worthwhile to consider.  We are talking 30% more weight, but this could be exacerbated by having a cold shop and really thick resin.  Ditto, the vinylester’s viscosity  I use doesn’t seem to be as affected by cold as the epoxy.  I should probably redo this again with a peel ply to see how that comes out but vacuum bagging really is a must if you are concerned about weight.

The last point I should make is strictly my observations and is anecdotal.  But every corner I have to make adds a LOT of weight and time so these weights are pretty good for flat areas but need to be increased a fair amount whenever there are a lot of curves and corners.  Overlaps obviously add material but corners also tend to be very resin rich and often get sanded too much and may require more material and time to fix (if you aren’t careful anyway).  The mold or plug building is made a lot more complex, too as is the vacuum bagging.  For example, laminating a deck as simple as Pegasus took twice the time it took to do the hull, even though the area was only 2/3.  So in general, I avoid corners and complex shapes as much as possible to reduce time and weight.

I have several digital scales and being the anal dude I am, I have a set of calibration weights that I used to test their accuracy.  So far, every scale has had errors of under .05% so these weights should be very good.

I hope these come in handy.

Dan

click here to download a copy of Dan’s Table of Weights spreadsheet

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