A threaded bronze, nylon or stainless steel shaft passes through a hole in the bottom surface of the hull. Choice of styles: external football-shaped head with water flow smoothed by a fairing block that also corrects for the deadrise (sideways slope of the hull); or round mushroom head thru-hulls, either semi-flush or flush mounted. They are most challenging to install, but likely to provide best signal quality. Displacement power and sailboats generally use thru-hulls.