short version to a complicated question
Nicholas, the short version is that a solid hull is one constructed of solid fiberglass while a cored hull is one that is constructed using a composite type constuction with fiberglass covering a core material such as foam or balsa wood. If, and that being the key word, the composite is done right it can be stronger and lighter than the solid constuction. There have been some issues with core construction though, SeaRay, a power boat company has been having a lot of problems with water intrusion and causing costly, and I mean costly repairs. One of the issues with cored decks and hulls has been delamination where the fiberglass and the core material separate. Maintenance is important in that at least every five years the deck fittings should be pulled up and rebedded (rechaulked) to prevent water intrusion. Dings in the hull or deck from dropping things should be repaired. Many boat builders are building solid fiberglass up to the waterline and then cored construction above which I guess is a bit of a comprise. Anyway this is kind of the short answer as I said and I hope it helps .Charlie