How many layers of fiberglass do I need for boat stringers?
Similarly, how many layers of fiberglass do you need for stringers?
The two stringers have two layers of 1708 on each side. They are glassed too the hull with "two" layers of 1708 as shown in Travis' schematic. Bottom line, these two stringers will never crush, rot or move.
Additionally, how many layers of fiberglass do you need for a car? two layers
Correspondingly, how many layers of fiberglass do you need for a boat hull?
Two layers is the absolute minimum, three is better The more prep time between the layers the stronger the finished product will be.
Do I need to sand between layers of fiberglass?
There is no need to sand in between layers. Kind of. When a layer of mat has cured, there will be fibers sticking up. If these fibers aren't knocked down with a quick once-over with coarse paper, they'll create little air bubbles when the next layer is applied.