- Anything that lies inside the hull, outer rails, or outer rigging of a vessel.
Probably the 14th century.
Technically, anything inboard can (probably) also be “aboard” a vessel. Simply put, if it’s not touching the water, and it’s within the confines of the hull, mast, or outermost rigging, then it’s said to be inboard. Another way to think of it is: towards the center line of the vessel.
Rogers, J.G. (1985). Origins of Sea Terms. Mystic Seaport Museum.