: When does the desired lightness of the craft create strength limitations. I
: am sure the answer is rather complicated and dependent on a whole host of
: factors. I have just completed the forms for my son's Grebe. He is 90 lbs.
: I weigh 235 lbs. and will be building an Outer Island next. I would like
: to not limit where we can paddle our kayaks.

All strength is limited. As such, any layup is a trade-off between strength and lightness. There is also a consideration of how easy/mistake-tolerant the building method is. Very thin strips are lighter but allow less leeway for error. Multiple layers of lighter glass are stronger than one of heavier glass, but more layers takes longer. With good glassing skills you can might be able to keep multiple layers lighter as well, but it is easier to add more resin than required.

There is no one answer for what is "strong enough" it depends on the load the boat will carry, the conditions were it will be used, and the care with which the paddler will use the boat. The best way to determine how much strength you personally need is to build a boat and go paddling. The "standard" layup of 1/4" strips covered with 6 oz glass, (doubled up on the bottom) is strong enough for most uses. Some people will need stronger, and it will be overkill for others. It also gives inexperienced builders more wood to work with as they correct their mistakes.