(N) :
In sailing and warfare, to be hull down means that the upper part of a vessel or vehicle is visible, but the main, lower body (hull) is not; the term hull up means that all of the body is visible.
(N) :
In sailing and warfare, to be hull down means that the upper part of a vessel or vehicle is visible, but the main, lower body (hull) is not; the term hull up means that all of the body is visible.