ESTABLISHMENT OF REFERENCE PLANES

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