Design and construction of large tankers in Japan 1

This lecture first presents an outline of research work by which many troublesome problems in the design and construction of large tankers were solved, and secondly introduces the largest tanker ever built in Japan, the Nissbo Maru, of 130,000 deadweight tonnage.

With regard to design of such tankers, two points, that is,

(1) reduction in length of ship (L), and

(2) increase in depth (D),

should be taken into account from the standpoint of weight saving and of easy fabrication.

Researches into structural problems of tank parts and into the dynamic pressure of cargo oil tank, due to ship motions, are described briefly, and show that the maximum impulsive pressure in model tests may be up to 5 times the static fluid pressure and may be observed at the tank top when the natural period of fluid in the tank is resonant with the oscillation period of the ship.

Special care should be taken in the detailed design of longitudinals, struts and so on, otherwise cracks will initiate easily at the point of stress concentration.

As regards hull construction practices in such large tankers, there seem to be no special problems except in the fabrication and welding of very thick plate of up to 50 mm thickness. Very thick plates thus offer several problems to be solved such as groove shapes, application of “Unionmelt”, doubling plate, weld cracking, and back-wave welding technique, etc. Brief discussion and some test results on these problems are included and mention is made of the superiority of KZ-type groove for automatic single-pass submerged-arc welding and of “Uranami” Welding electrode (which offers a perfect one-side welding without backing plate).

Finally, construction methods for large tankers are briefly introduced to give an idea of the hull construction of such large tankers in the building berth.