An entrapment tunnel watercraft vessel having three hulls consists of a
main hull and two amas arranged outboard of the main hull with the keels
of the three hulls being parallel. The main hull is a narrow, vee hull
with variable, rearwardly decreasing deadrise. The amas have very fine
bows and narrow, asymmetric deep-V hulls, with nearly vertical slab
outboard sides above their keels and variable reverse deadrise on their
inboard sides with the reverse deadrise angles decreasing from bow to
stem. The tunnels on each side of the main hull are formed by three
distinct surfaces, the sides of the main hull above its chine, the
reverse deadrise inboard sides of each ama upward from their keels and a
ceiling surface transversely spanning the aforementioned sides and having
rearwardly increasing deadrise and rearwardly decreasing width. The
tunnel ceilings slopes down from the bow to a section aft of midship
where the ceiling height above the keel remains essentially constant. At
speed the craft generates substantial amounts of lift and positive trim,
thereby reducing the forward wetted length of the immersed tunnel ceiling
and the apex of the ceiling is approximately at the craft dynamic
waterline. As a result the watercraft vessel has improved seakeeping,
stability and weight carrying ability.