ment, the performance of training and elevation space
alignment, the establishment of benchmark and tram
reference readings, and the combat/weapons systems
smooth log.
ESTABLISHMENT OF REFERENCE
PLANES
The first major alignment step accomplished by a
support activity is the establishment of reference
planes. Referencing surfaces consist of the ship base
plane (SBP), master reference plane (MRP), center-
line reference plane (CRP), and weapons-control ref-
erence plane (WCRP).
Ship Base Plane
The ship base plane (SBP) is the basic horizontal
plane of origin. The SBP is perpendicular to the ship’s
centerline plane and includes the base line of the ship,
but it is not necessarily parallel to the keel of the ship.
The SBP is used in establishing the MRP.
Master Reference Plane
The master reference plane (MRP) is the first
physical plane that is established for combat systems
alignment. The MRP is parallel to the SBP and is
represented by a master level block or plate, usually
located on a lower deck of the ship. The plate is in-
stalled, aligned, and leveled only once after hull inte-
gration and is never adjusted thereafter. The master
level plate serves as the reference for machining the
foundations of the combat systems equipment
throughout the life of the ship.
Centerline Reference Plane
The centerline reference plane (CRP) is estab-
lished during ship construction by the installation
activity. It is the plane containing the ship’s centerline
and is perpendicular to the MRP. The CRP is the ref-
erence used to establish train zero alignment of all
combat systems equipment. The CRP is used through-
out the life of the ship.
Weapons-Control Reference Plane
The weapons-control reference plane (WCRP) is
the plane to which the foundations and the roller-path
planes (RPPs) of all combat systems equipment are
leveled. The WCRP is used throughout the life of the
ship to determine RPP parallelism between the equip-
ment of the combat/weapons systems.
PLACEMENT OF REFERENCE
MARKS
The second major alignment step is the placement
of centerline marks, offset centerline marks, and
equipment benchmarks, which are performed by a
shipyard or support activity.
Centerline Marks
Centerline marks are established during initial
construction to represent the ship’s centerline. Small
plates (at least three forward and three aft) are in-
stalled at intervals along the centerline to mark its
location. Small plates are also installed in certain ship
spaces to mark the location of the centerline.
Offset Centerline Marks
Offset centerline marks are also established during
initial construction to facilitate combat systems align-
ment. The offset centerline is normally established
parallel to or perpendicular to the ship’s centerline.
Offset centerline marks not parallel or perpendicular
to the ship’s centerline are stamped or marked with
the angles relative to the ship’s centerline. Offset cen-
terline marks are also established, as required, in
interior compartments of the ship to facilitate the
alignment of the combat systems. Both the centerline
and offset centerline marks are installed to preclude
the necessity for repeating the centerline surveying
during subsequent alignment.
3-13
