Major conversion means a conversion of an existing ship -
(1) That substantially alters the dimensions or carrying capacity of the ship; or
(2) That changes the type of the ship; or
(3) The intent of which, in the opinion of the government of the country under whose authority the ship is operating, is substantially to prolong its life; or
(4) Which otherwise so alters the ship that, if it were a new ship, it would become subject to relevant provisions of MARPOL not applicable to it as an existing ship.