RUS, it does not matter how you put strength in a structure, it only matters that you have enough strength for the structure to not collapse.
Whether it is a monocoque design, or a separate frame chassis (what you call a spider) or traditional framed and planked construction...If your boating
authority says that a hull
is not strong enough and needs additional structural members, they probably are right. Generally using stiffening members like that will be stronger (for the weight and cost) than trying to simply use a stronger hull
. Even metal hulls have taken damage from wave action against unsupported areas.