Originally Posted by jameswilson29
What would happen if this kind of eggcrate grid were added to a flexible-hulled boat with an interior liner?
Suppose someone took out the liner floor with a circular saw, reinforced the hull area with additional layers of fiberglass, installed a grid around the keel area from the mast aft to the engine compartment/cockpit bulkhead, and attached it to the interior liner. I have pondered doing this, with the addition of a bridgedeck to limit cockpit volume and water ingress to the cabin through the companionway.
Would this make a flexible-hulled boat more seaworthy, or merely transfer energy and stress out of the keel area to the edges of the eggcrate grill so the hull would experience greater stress in those areas?
If reinforcing a flexible hulled boat, would one have to start from scratch by removing the boat's entire liner, install complete bulkheads and grid?
Or is it a matter of a flexible-hulled boat best remains a flexible-hulled boat and a rigid-hulled boat best remains a rigid-hulled boat?
Firstly, it is never a good idea for fiberglass to be flexy - it essentially flexes by breaking down a little each time it flexes. You can see (or rather, hear) this for yourself. Take a piece of polyester laminated glass, say 3" wide by 12" long by 1/8" - 1/4" thick and bend it with your hands - you will hear the crunching of the glass/resin bond breaking down.
Incidentally, if you try the same thing with epoxy laminated glass, if you can even bend it, you will not hear those sounds, at least until you flex it a ridiculous amount - the resin is much less "hard" or brittle.
As to the transfer of stress to the outer edge of the grid - you are essentially referring to the creation of a stress riser. While it is conceivable this could happen if you built some sort of narrow "box" around the keel area, like a low centerboard case, it will not happen with a proper grid. That is the purpose of the grid - to diffuse the stresses over a large area of the hull so no localized area has a large load on it.
As an extreme illustration of this process - a keel with only small square, sharp edged "washers" on the keel bolts can and have pulled through the bottom of a boat. The forces are concentrated on the edges of the "washers" in a manner like you are concerned about.
If the bolts are backed with long, wide plates, they will not pull through the bottom but without a grid as well, the bottom of the boat could possibly still flex somewhat.
Add in a large, diffuse grid like Faster did - problem solved.