On a boat, generally speaking, anything that you can do to save weight is a good thing. Many high-end powerboats have granite counters, big generators, and plenty of other stuff that has to be lugged about, all increasing the work that engines have to do and thus leading to decreased fuel economy. Obviously, things such as shelves ideally should be stiff, lightweight, and strong. One way of doing this is to use cored material which can be both light and strong, but things like foam cored plywood are very expensive. Looking for a cheaper alternative, I now make shelves and other components as shown in the sketch above. Essentially a torsion box, panels are cheap and quick to make and far, far cheaper than having to buy cored ply at over $400 per sheet.
The sketch shows how I built some shelves for the boat which were almost one and a half inches thick with a teak lipping on the front. The strength comes from the method of construction rather than from the material itself, so I use western red cedar for the solid wood strips. The strips themselves are a half inch thick by whatever the width needs to be, which in my case, was just over an inch. Spaced three inches apart, with the ribs glued in place with epoxy, the panels are super strong and won't flex under the weight of pilot books and other equipment. There is a little bit of work in it to make the panels, but I can swallow that given that I saved myself hundreds of dollars and a ton of weight into the bargain.