There are various methods used in the building of a ship on a building berth or in a drydock, but a popular method nowadays is the Block Assembly Method in which sections of the ship are pre-fabricated in the shops or adjacent to the slipways. These pre-fabricated sections are installed on the building berth proper in a pre-determined sequence starting from one point. The Yokohama Shipyard and Engine Works of Mitsubishi Nippon Heavy Industries, Ltd. has built more than twenty tankers since the termination of the war, but has gradually abolished the aforementioned system of starting construction with only one point, and adopted instead the method of starting construction with the three points e. i., Midship. Bow and Stern, simultaneously. When a number of ships are under construction at the same time, the labour force for hull erection is concentrated on one ship only so that erection of the hull may be completed within the first half of the construction period on the building berth and all the work of hull, machinery, and outfitting may be progressed more rapidly. This system promotes the progress of construction and also is advantageous in spreading the work over the various shops in the shipyard, promoting efficiency, constant use of facilities, etc. It may be added as an example of efficient utilization of facilities, that with the above mentioned system one large tower crane is capable of installing the blocks for two 40, 000 DWT Tankers under construction on adjacent berths.