Ship Data - Axis

The axis parameters which consist of the pivot point's location (defined by co-ordinates) and the swing angle are primarily of concern when considering calculations for offshore structures.

For ships, these values are usually all zero except X, which should be at amidships, that means, LBP/2.

• X:

  The longitudinal location measured from the AP, in meters.

• Y:

  The transverse location measured from the centerline, positive to starboard, in meters.

• Z:

  The vertical location measured above the baseline, in meters.

The Swing Angle (degs) is the angle through which the x-axis is rotated to starboard about the pivot point. Entering a swing angle changes the planes in which heel and trim occur, affecting values such as KMT and therefore stability. However the internal reference axis of the vessel (usually defined at the AP) maintains its relative location and orientation within the vessel; thus items measured using this axis system such as LCB and TCB, remain unaltered.

Note:
The values of MCTC in the hydrostatics are incorrect when a swing angle is entered as the LBP is used for the calculation and not the notional length in the altered x direction.