There are 2 load conditions that I would consider. There might be more, but I can't think of them right now.

1. The bending of the kayak along it's length.

2. The impact load caused by landing on a rock.

If you take 60" cloth and put it on an 18' boat at the most extreme angle you'll be able to put it on at slightly more than 16 degrees. Most people put the cloth on at even less than this which means that they are strongest in the longitudinal bending direction. To make the angle even greater (like 30 degrees) would require overlapping the plies (side by side) to get enough width. See attached photo.

Our kayaks are plenty strong in the longitudinal direction as Nick can attest to when he had both ends of his kayak sitting on rocks and the water went out from under his kayak. His kayak didn't have any problems supporting his weight. My triple was also tested when Mike Hanks lifted the front end out of the water to drag it on shore with Shawn, his wife, and a ton of gear in it. Thanks Mike Shawn jumped out though, so his weight doesn't count.

When impacting a rock, the stress goes in all directions.

My contention is that the kayak might be better for impacts if say (3) 4oz plies were laid at (-30, 0, 30) as shown in the picture instead of (2) 6oz plies at (-15, 15). This might reduce the strength in the longitudinal direction though.

I still build my kayak hulls using (2) 6oz plies (each side) at around (-15, 15). Why? Because it has been proven to work. Until I actually do the analysis and test some panels, I plan to continue doing it this way.

Some day (if I were to ever have a bunch of spare time, yeah right) I might test this theory by making some panels. I would test the landing on a rock comparison by placing the panel over the end of a bucket and then putting weight in the middle of the panel. This weight would be applied on say a 1" diameter steel ball.

I would test for longitudinal bending of the kayak by bending a panel that is supported at 2 ends. The test would be for comparison purposes only since the kayak would really be in compression on the deck and tension on the hull when supported at the ends.

Build it how you want, but remember that the way most people have been doing it has been proven to work.