PURPOSE: To miniaturize in size a float crane and contrive to save cost, by a method wherein a constructed ship is launched by suspending it by both a float crane and a dock-side crane.

CONSTITUTION: At a position proximate to a gate door 2 of a dry dock 1, a small-type ship 5 is constructed so that the longitudinal direction thereof coincides with the width direction of the dock 1. When launching the ship 5, the ship 5 is supported by two beams 10 placed in the transverse direction of the ship 5, ends of the beams 10 on one side are suspended by a movable crane 3 provided on the dock side, while the other ends are suspended by the float crane 4, and the ship 5 is alighted on water by combining a movement of the crane 3, a slewing of a jib crane 3a and a movement of the float crane 4. Accordingly, since the ship 5 can be launched by suspending it by both the float crane 4 and the dock-side crane 3, the size of the float crane can be reduced to about 1/2 of that of a float crane used in the conventional methods, and hence cost can be saved.