Optimum Hull Structure

Simplified hull structure and enhanced structural strength

Apple Slot

Comparison between Conventional Structure and New Structure with Apple Slot
Apple Slot
Conventional double hull structure and new double hull structure with Apple Slot are compared in VLCC's (Very Large Crude Carrier) case below:

Web plates of main transverse members such as floor plate need to be fitted with stiffeners (a kind of reinforcement member) with required spacing to prevent the buckling of the structure. In VLCC's conventional double bottom floor structure, vertical stiffeners are directly fixed to every longitudinal frame by welding. In the Apple Slot structure, on the other hand, a combined stiffening arrangement of vertical stiffeners with necessary spacing (to ensure the rigidity of the entire floor structure) and horizontal stiffeners (to divide the floor plate between these vertical stiffeners) is adopted to prevent the buckling of the floor plate.
In this structure, because the vertical stiffener is omitted, the load transmitted from the longitudinal frame to the web plate of the main transverse member is increased, but by making the slot opening have a special shape with oval (Apple Slot), the stress concentration there is relieved.
Conventional Slot
Apple Slot
* High stress parts are indicated in yellow.
In spite of omitting the vertical stiffener, the Apple Slot structure shows lower stress levels around the slot.

The Apple Slot structure ensures a higher structural reliability because it enables reduction of welding works at connecting parts between face plate of longitudinal frame and vertical stiffeners on the floor where the stresses are so high as to cause fatigue damage.

Further, because of reducing the number of vertical stiffeners and brackets connected to the longitudinal frame, the Apple Slot structure is advantageous in simplifying the structure and automating the construction process.


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