184_NAVIGATION_SYSTEM_ALIGNMENT.pdf

184 NAVIGATION SYSTEM ALIGNMENT

184a. Installation and Alignment Leveling, positioning, and relative orientation of instrument mounting surfaces within the specified tolerances is critical to proper operation of their associated systems. Surveyors selected to perform this work shall have previously demonstrated the ability on similar projects to achieve the accuracies specified herein. Written certification shall be submitted establishing the credentials of surveyors with a description of the work previously performed.

A written Survey Plan shall be prepared prior to installation of the Master Reference Block (MRB) or any other survey items.

A MRB shall be provided, consisting of a granite reference block aligned to the design waterline to within 9 seconds of arc in the x, y and z axes. The block shall be mounted on a sufficiently rigid foundation and supported in a steel box by 12 swivel leveling threaded bolts, which shall also be used to position and level the block. After installation and alignment of the reference block to the satisfaction of the ConRep, the block shall be fixed in the box with poured epoxy. Unless otherwise specified inertial measurement units (IMUs), navigational antennas, radars, directional finders, gyrocompasses and each sonar projector and receiver shall be aligned in the x, y and z reference plane to the MRB in accordance with the required specifications in Table 184-1, but in no case to a tolerance of greater than the manufacturer’s recommendations.

Local permanent benchmarks, referenced to the MRB, shall be installed at the following locations in such a manner and quantity so as to permit accuracy in resurvey and positioning of installed and future equipment:

a. at each transducer location,

b. in the centerboard trunk at the centerboard maintenance position,

c. on the bottom of the centerboard,

d. at the inertial measurement units and GPS antennas,

e. at the gyrocompasses,

f. at points on the aft and forward decks visible to the mission navigation antennas,

g. on the Main Deck under the center block of the stern gantry (as far aft as possible).

In addition, each transducer housing and mission sea chest shall have a forward and aft lineup mark, each consisting of two triangles with a center punch mark, separated by 5 cm.

Resulting lineup marks shall be parallel to ship’s centerline.

The ship’s vertical centerline plane shall be established by the survey and is defined as a plane which is perpendicular +/- 6 minutes of arc to the MRB and which is parallel the longitudinal centerline of the center vertical keel.

The following horizontal surfaces shall be coplanar and aligned in azimuth with the ship’s vertical centerline plane to the accuracies specified. In order to avoid measurement error, these surfaces shall be aligned simultaneously.

a. Top surface of the multi-beam mounting frame flange; or, the underside of the “flange counterpart”

b. The IMU attitude sensor mounting plate

c. The Master Reference Block

d. The gyrocompass foundation plates.

The fore/aft axis of each surface shall be parallel to the ship's vertical centerline plane +/- 6 minutes of arc.

The fore/aft axis of each gyrocompass foundation shall be parallel to the ship's vertical centerline plane +/- 6 minutes of arc. Surfaces “b” and “c” of the gyrocompass shall be parallel to the gravity plane in fore/aft and athwart ship directions to +/- 6 minutes of arc. Surfaces “a” and “b” of the gyrocompass shall each be parallel to surface “c” to +/- 6 minutes of arc. Once each gyrocompass foundation is aligned, it shall be securely locked into position.

After the IMU and the Master Reference Block have been aligned and installed, the Contractor shall determine the offset or difference in azimuth between the gyrocompass mounting plates and the Master Reference Block. Each of these readings shall be witnessed by the ConRep.

Centerboard-mounted transducers shall remain aligned to the local permanent benchmark on the centerboard within +/- 6 minutes of arc.

Following the installation of all equipment involved in the survey, the Contractor is to measure the installed distances using an "X", "Y", and “Z" coordinate system. The center of the system (0, 0, 0) shall be the top surface of the granite reference block at the intersection of the fore/aft and athwart ship scribed lines. The "X" axis shall lie parallel to the centerline vertical plane with its positive toward the bow. The "Y" axis shall lie perpendicular to this plane with its positive toward starboard. The "Z" axis shall lie in a plane parallel to the ship’s centerline vertical plane with its positive toward the keel. Distance measurements shall be made to the acoustic center of each multi-beam transducer array as defined in the manufacturer’s tech manuals, to the center of the reference mark on the top of the IMU (using the label on the top plate of the IMU to identify its sensing axis) and to the phase center of each inertial reference system antenna. Measurement tolerances shall be in accordance with Table 184-1.

All survey readings taken shall be recorded and incorporated into a Navigation Systems Alignment Report.

Table 184-1 – Survey Specifications

184b. Technical Documentation Navigation Reference System Surveyor credentials shall be provided.

A comprehensive written Survey Plan shall be prepared which completely describes the procedures to be used to meet the survey requirements of this SOR. The Survey Plan shall include a step-by step procedure, list of instruments to be used, sketches showing lines of sight, and methods of verifying that the required accuracies have been attained.

A Navigational System Alignment Report shall be provided. The report shall document all readings taken during survey operations and shall describe the as-installed accuracy of each the MRP, each benchmark and each sensor and sensor mounting surface.