Very interesting observations Lee, thank you!

Ive been thinking of a jig to test 12 x 12 panels in, something like a press using a bottle jack, and a scale to show approximate failure and delamination points using various glass over strip panels. Im thinking if I had a way to support the panel around its perimeter, and push through it while measuring the applied force, that it would be something similar to the stress a hull gets on impact, and offer some useful data. Any ideas on how I could measure it?

> Bram ,

> Before I moved to annapolis I purchased Ruel Parkers book on sharpies,
> while fantasizing about the boat that would take me away from myself I was
> struck by Parker's dislike for fiberglass and encouragement of the use of
> Xynole polyester cloth for a small boats exterior of the hull as well as
> the use of polyester tape at filleted joints. Not knowing what a sponge
> some cloths are for resin i asked around kit builders about other
> coverings, got a generally why bother attitude. Which I now can understand
> after building an ice-breaker of a boat covered in polyester cloth
> >50lbs for 16ft boat. Bought some 5oz polyester cloth,5oz kevlar,10oz
> unidirectional tape,4oz S-glass,6 oz E-glass, kevlar , glass,and polyester
> tape,then went to town with a very unscientific collection of 4mm okume
> approx. 8"sq. I didn't weigh anything , I just made sure to be
> consistant as possible while glassing. After pieces were cured for about a
> week, my scientific testing apparatus was a concrete step that I would put
> the panel against then press into untill the panel fractured, I was more
> interested in how the composite fractures as well as any gross differences
> that I could feel with a foot,hammer,and screwdriver attacking the panel.
> I wanted to get a simple intuitive sense how some laminates worked.

> So for the most part each piece different from the other,there was no
> control,a wide variation in forces applied,according to strength of that
> mornings coffee.

> All that said this is what I noticed that was important to me, a laminate
> with 4oz. s-glass on both sides bent more easily compared to a laminate
> with 6oz on both sides, while the 6oz panel was stiffer and fractured at a
> slightly higher effort the entire laminate fractured with most of the
> glass and wood fracturing completely,in other words I could bend it back
> and forth a few times and have two pieces. The surprising thing about the
> 4oz s-glass was how far it could bend and spring back,when bent to a
> complete fracture the fractured glass and wood was bent with a series of
> more parallel like fractures unlike the 6oz glass which pretty much
> shattered along the axis of the threads as well as large seperations in
> the plywood itself. In simple punctures and dropping a concrete breaking
> bar from about a foot the other surprising thing was that the 6oz E glass
> laminates fractured primarily along the axis of the cloth and for a larger
> distance from the puncture than the 4oz S-glass piece. Also the fractures
> in the s-glass piece didn't travel as much along the axis of the cloth. So
> while the cost of S-glass is ridiculous compared to regular glass it
> certainly appears to have better characteristics.

> Just for fun I laminated a piece with 4oz polyester,4oz s-glass on one
> side and 4oz on the other. After bending and stomping I had a very floppy
> piece of plywood that pretty much stayed together, similar to what kevlar
> would be like except that the kevlar appeared to delaminate at the wood a
> little more than the glass/poly combo. That 8oz of glass/polyester cloth
> probably weighed as much or more that 10oz of regular glass but the way it
> fractured made me think that super strong cloths like kevlar are kind of
> on their own as a skin,the polyester cloth had more give and appeared to
> stay with the plywood as it fractured. The other things I noticed may
> sound ridiculously obvious but here goes, More cloth made a much stronger
> panel, a layer of 4 oz Sglass on top of regular 6oz eglass made a very
> tough and puncture resistant panel.

> The undirectional carbon made an incredibably stiff panel that snapped
> quite crisply, all fractures developed at the edge of the tape, The
> difference between plywood and that heavy carbon i used is so great that
> the stuff kind of scares me. It ain't natural. Can't wait until carbon
> nanotubes become the next miracle material. We'll all be paddling black
> crystal!

> Other interesting observations, with fillets. I made about 6 120degree
> panels with misc cloths just on the inside, I was lazy and didn't finish
> the outside edges like a boat. Don't remember the exact combinations
> except that when all of them were stepped on they broke at the edge of the
> fillet, the ones with regular 1 1/2"tape broke right at the tape
> edge, one with carbon layed perpendicular to the fillet was very tough
> didn't break,the plywood simply went all to pieces, somehow using carbon
> with plywood just doesn't seem right. One of the pieces with 3"
> polyester tape along the fillet stayed together. The conclusion I came
> from with this is that a thick fillet,with 1 1/2" tape leaves a lot
> of unnecessary strength through the joint and comparatively little beyond
> the tape. Seems to me that eliminating 9oz glass tape,using just enough
> fillet to maintain a joint thickness just a little thicker than the
> joining panels then using 4 oz cloth throughout the inside then another 4
> oz strip over the fillet will yield a stronger panel throughout as well as
> a sufficiently strong joint. Don't think this applies to hull deck seam
> though, tighter angle. The general idea is to replace excess fillet with
> glass extending further beyond the joint.

> Other observations, about cracks and fractures propogating along the axis
> of the threads, regular glass did this a lot compared to the s-glass and
> plastics. So George's preference in using multiple layers makes lots of
> sense in reducing the propogation of fractures. Light kevlar and s-glass
> is a killer combo.

> When laying 4oz onto the polyester there was enough resin soaked into the
> polyester to wetout the glass just by pressing it on.

> Honestly don't remember much else, the neighbors didn't mention anything
> about my whacking stuff in 45 degree weather every other day.

> So it's all pretty common sense, too much resin just wastes resin, 6oz e
> glass is plenty strong and cheap, how and where glass is used is more
> important than simmply using 4 oz instead of 6 oz or KEVLAR instead of
> whatever. cheerio