3 October 2005
COORDINATE SYSTEMS. The various coordinate systems used for
ships and mooring design are described below.
Ship Design/Construction Coordinates.
A forward perpendicular point
(FP), aft perpendicular point (AP), and regular spaced frames along the longitudinal
axes of the ship are used to define stations. The bottom of the ship keel is usually used
as the reference point or "baseline" for vertical distances. Figure 3-2 illustrates ship
Ship Hydrostatics/Hydrodynamics Coordinates. The forward
perpendicular is taken as Station 0, the aft perpendicular is taken as Station 20, and
various cross-sections of the ship hull (perpendicular to the longitudinal axis of the ship)
are used to describe the shape of the ship hull. Figure 3-2 illustrates ship hydrostatic
Local Mooring Coordinate System. Environmental forces on ships are
a function of angle relative to the vessel's longitudinal centerline. Also, a ship tends to
move about its center of gravity. Therefore, the local "right-hand-rule" coordinate
system, shown in Figure 3-3, is used in this UFC. The midship's point is shown as a
convenient reference point in Figures 3-3 and 3-4.
Global Coordinate System. Plane state grids or other systems are often
used to describe x and y coordinates. The vertical datum is most often taken as relative
to some water level, such as mean lower low water (MLLW).
Ship Conditions. Loading conditions are defined in NAVSEA
NSTM 096. There are three common conditions or displacements that a ship has at
various stages including:
"Light Condition" This is the ship condition after first launching.
"One-Third Stores Condition" This is the typical ship condition during ship
repair, as indicated in SUPSHIP docking/undocking records.
"Fully Loaded Condition" This is the ship condition during operations.