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