Defining the installation parameters for the motion reference unit (MRU)
The physical location of the motion reference unit (MRU) relative to the transducer is required to allow the MS70 to adjust for roll and pitch as accurately as possible.
Prerequisites
For accurate location of the motion reference unit (MRU), you need the detailed vessel drawings. The information about the installation angles must be retrieved from the reports provided by the personnel that did the actual installation. For maximum accuracy, we strongly recommend that you use the information provided by a dimensional survey.
Note
Determining the relative positions and orientations of the sensors and the transducer with high accuracy is important. This requires professional land surveying done by qualified and trained surveyors using proven survey equipment and methods . We recommend that you use third party consultants with well proven experience with vessel dimensional control. The information provided by the dimensional survey is entered into the MS70 software as installation parameters.
Neither tools nor instruments are required. The MS70 is switched on and working in normal operational mode.
Context
The motion reference unit (MRU) measures the roll and pitch motions of the vessel. Some sensor models also measure heave.
On the MRU Offset page, you must define the physical location of the motion reference unit related to the "official” ship origin that was defined by the vessel designer and/or the shipyard. The rotation around the X, Y and Z axis is used to compensate for misalignments made during the physical installation of the motion reference unit. Such misalignments occur if the sensor is not placed in parallel with the vessel’s horizontal and/or vertical planes. The required accuracy of the offset and rotation angles depends on the accuracy requirement for the MS70 data.
Image
A Rotation around the X-axis: In the positive horizontal direction (forward), a positive rotation is clockwise.
B Rotation around the Y-axis: In the positive horizontal direction (starboard), a positive rotation is clockwise.
C Rotation around the Z-axis: In the positive vertical direction (down), a positive rotation is clockwise.
D Reference point (origin)
Note
The Kongsberg Seapath® - and other GPS systems - allow you to define the MRU location in the positioning system. If this is done, the MRU offset values in the MS70 must be set to 0 (zero) to avoid "dual compensation". The rotation information is normally not recorded by the positioning system, and must therefore be defined in the MS70.
Procedure
1 Open the Setup menu.
2 On the Setup menu, select Install.
Image
Observe that the Install submenu opens.
3 Select Instrument Offsets to open the dialog box.
4 In the Instrument Offsets dialog box, select MRU Offset to open the page.
a From the dimensional survey report, extract the relevant information.
b Insert the correct values. Do this as accurately as possible.
c Record the information in the result table.
d Select OK to save the chosen settings and close the dialog box.
Note
The Kongsberg Seapath® - and other GPS systems - allow you to define the MRU location in the positioning system. If this is done, the MRU offset values in the MS70 must be set to 0 (zero) to avoid "dual compensation". The rotation information is normally not recorded by the positioning system, and must therefore be defined in the MS70.
Result
Motion reference unit (MRU) offsets
X-offset  
Y-offset  
Z-offset  
Installation angle X (αX)  
Installation angle Y (αY)  
Installation angle Z (αZ)