Page 142 of 254
Part No. 96000001
• If possible, the vessel will be berthed alongside a quay or dock that has a survey
benchmark located nearby.
• If a survey benchmark is not located close to the berth, then the surveyor will have to
run a transit from the nearest, suitable, local survey benchmark to establish a point
on the quay that has a well-defined position. From this point, another point should
be established along the quay to form a baseline.
• When the vessel comes alongside, all lines should be made as taut as possible. The
gyro should be allowed 2 hours to settle down after the vessel has come alongside.
• The stern of the vessel should be measured, with a metal tape, to determine the
centre point of the stern. A survey reflector will be placed at this position. Another
survey reflector will be placed exactly at the bow. It will be verified that the reflectors
are accurately placed on the centre line of the vessel by either measurements or
survey techniques.
• The surveyor will set up on one benchmark; a round of readings will be taken from
the benchmark to the fore and aft reflectors. Simultaneous to this, the survey
personnel will record the gyro heading as it is read by the survey computer. Any
variation between the digital output and the physical gyro reading should be
remedied before the commencement of readings. It is recommended that the
personnel on the vessel and the surveyors on the quay be in constant communication
to assist in coordinating the measurements.
• One round of readings will be considered to be not less than 30 sets, a set being one
reading each from the bow and stern reflectors.
• Upon completion of the round from benchmark one, the surveyor will move to
benchmark two and repeat the process.
• Upon the completion of all rounds, from the two benchmarks, the vessel will turn
about. With the vessel, now heading on the reciprocal heading, the gyro will be
allowed at least 1 hour to settle down.
• When the gyro has been given sufficient time to settle down, a further series of range
and bearing measurements will be made in the same manner as before.
When all readings are completed, the surveyor will calculate the azimuth between the two survey
reflectors for each set of readings. The azimuth readings will be compared with the headings taken
on board the vessel from the gyro itself. If there has been little or no movement of the vessel, an
average can be taken of the azimuths and for the gyro readings and compared. By calculating the
standard deviation of the readings, the surveyor can determine the degree of movement during the
recording process. If the deviation is greater than the stated accuracy of the gyro, the comparison
readings should be based on simultaneous time.
If physical adjustments are required, they should be made and the calibration process repeated. If
the adjustment is determined to be minor and can be accounted for in the survey software, the
correction value should be entered and then verified using the calibration process. This check of the
calibration value can be an abbreviated version of the calibration process detailed above.
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