Fiddle, Faddle and Rot, Sir
Updated: Oct 4, 2022
Many modern, production, fiberglass (FRP) boats utilize longitudinal stringers for hull stiffening and engine supports. Typically, those stringers are cored, often times with wood. Water that has found its way below decks but outboard of the stringers can't find its way past the stringers to a bilge pump placed at the lowest part of the bilge. That's why builders place limber holes in stringers, allowing any water to travel past them on its pilgrimage to a bilge pump shrine.
Unfortunately, if the perimeter of the limber holes are not sealed properly, or the seal is damaged, water will make a pit-stop and set-up camp in the wood cored stringer. Wood + Water (especially freshwater) + Time = Rot and rot leads to a loss of structural integrity.
This problem is only made worse if a limber hole is plugged with leaves, lint, hair, or other water friendly materials that allow the water an easy on-ramp into the surrounding wood. A rust or tea colored stain around a limber hole is a sign of rot, and a sharp tool (slotted screwdriver) can tell the full tale.
A concern like this is not limited to stringers and limber holes; any place onboard where water may meet wood and the two get cozy should be well sealed.