If you hit something at sea and your hull is holed, could you reach the damaged part? Could you even see it? OK it would be almost impossible to make every section accessible. But are there parts which could be but are not?
One of the jobs you might consider during the winter lay-up might be to plan a grand opening of the lockers etc that could be made easier to get inside. You might start with the bilges. How easy is it to lift the sole? Probably some of it, but what about the other areas? What if the very place you can't remove, is where the hole occurred? Concealed compartments under the sole can create large voids, formed by frames and bulkheads, where there is no inspection hatch. If you can't reach it you can't plug it. Result - boat sinks?
Many GRP boats have a weak point where the deck and the hull are joined together. Some are bonded, some have overlapping elements, and some are just screwed together. The deck joint is a potential opportunity for water to enter the boat and guess where it ends up? Exactly, down in those in-accessible spaces where you might not be able to remove it. What about dodgy plumbing? Same scenario, draining into the voids, can it escape?
You possibly took it for granted that the builder created limber holes? Why not find out? If the area is sealed how are you to know until your boat starts very slowly to become sluggish, probably too slowly for you to notice, meanwhile she settles lower in the water. Carrying several hundred gallons of water would do that. What if your stringers are something less than solid? Maybe plywood apparently safely sealed, but actually a paint job, not encapsulated in glass. Result - the core rots, the strength is lost and now you have a floppy hull. If your boat is relatively new maybe there will be many years before the worst happens. But why allow it to start? If you are buying second hand, beware, even your surveyor will not have access to the concealed spaces.
What if your builder has filled your spaces with foam? Sounds like a good idea. Might help her not to sink? Probably deadens sound also. It does not mean that water can't seep into the open spaces within the foam. As it will likely be in contact with structural parts such as bulkheads then the same insidious relationship will develop. Would you allow a similar situation to develop in your house? Your surveyor will simply note that he cannot access these areas and therefore the problem is yours.
What can you do?
It's not that difficult to solve. In principle you need to create hatches over the concealed areas. Start with the sole and the carpet. There is no need for it to be secured with fixings as it is at home. Velcro should provide enough grip to avoid it wandering. Lift it and determine where the dividers are located, any self contained compartment should have a hatch. A location that is less than easy to access is just where you should make sure that hatch is provided. In cases where major structures like a galley unit inhibit your plans, then cut inspection holes so that you can shine a torch into the void to check if water is accumulating. Make sure that there is no hidden wiring where you are cutting.
Always cut a pilot hole to determine the material thickness. If the space is filled with foam, there is no point in cutting a hatch, an observation hole will be sufficient. Whenever you can create limber holes to allow the water to escape to a point where a bilge pump can evacuate it; make sure the holes edges are sealed to prevent rot.
The exact specification in terms of materials and construction will be determined by your specific boat. Care and patience should result in a drier and safer boat and you will certainly be more familiar with her more private parts.
