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Figure 17 shows a worked example of calculating the XY lever arm and indication of sign convention
(positive/negative) when the Merlin LT system is mounted in two different positions. Other positions are acceptable.
In the two examples, the measured offsets are:
•
Example 1: X = 0.9, Y = 1.8.
•
Example 2: X = -0.5, Y = -1.5
The Z / height value to the Merlin LT measurement datum point has been assumed to be 1.0 m, but this must also
be measured from the IMU/CoG.
For this measurement, it does not matter whether the Merlin LT is facing fore or aft: the measurement is to the
measurement datum point in the centre of the base plate.
Sign conventions may differ between different navigation packages.
The lever arm may be measured with a tape measure or with professional survey equipment. Either way, the
suggested tolerance for measuring these distances is <5 mm. A measurement outside of this tolerance may result
Forward / Y positive
Starboard / X positive
Example 1
Merlin measurement
datum point is:
X = 0.9 m
Y= 1.8 m
Z = 1.0 m (assumed)
Example 2
Merlin measurement
datum point is:
X = -0.5 m
Y= -1.5 m
Z = 1.0 m (assumed)
Vessel IMU/CoG
X = 0.0 m
Y = 0.0 m
Z = 0.0 m
Figure 17 Examples of offsets to the Merlin LT measurement datum point
