Prerequisites
For accurate ship dimensions you need the detailed vessel drawings. You need a printed version of each drawing. Each drawing must be to scale.
Procedure
|
1 |
Define the location of the origin in the coordinate system.
The origin is the common reference point where all three axis in the vessel coordinate system meet. All physical locations of the vessel’s sensors (radar and positioning system antennas, echo sounder and sonar transducers,
motion reference units, etc.) are referenced to the origin. In most cases, the location of the vessel’s "official" origin has been defined by the designer or shipyard. This origin is
normally identified with a physical marking, and also shown on the vessel drawings.
In this example we will establish the origin at the same physical location as the skipper’s seat on the bridge, however virtually
moved down to the waterline. The seat is located two metres to the starboard side of the vessel’s centre line. All sensors will then be referenced to this position.
|
• |
The depth readout from an echo sounder will be the Depth Below Surface (DBS) value contained in the NMEA DBS datagram. |
|
• |
Whenever a sonar is used with short ranges, this will provide a more precise presentation. |
If required, identify the location with a physical marking.
|
|
2 |
Measure the physical location of the transducer.
NoteIn this context, the transducer is regarded as a sensor.
|
a |
Draw a vertical line from the transducer and up. |
|
b |
Measure the vertical distance from the waterline and down to the transducer face.
This is the Z value. The value is positive because the sensor is located under the origin.
|
|
c |
Measure the horizontal distance in parallel with the X axis from the origin to the vertical line.
This is the X value. The value is positive because the sensor is located in front of the origin.
|
|
d |
Measure the horizontal distance in parallel with the Y axis from the origin to the centre line.
The sensor is on the centre line, but the origin is located on the starboard side. This is the Y value. The value is negative because the sensor is located on the port side of the origin.
|
|
e |
Type the values you have found for X, Y and Z into the Transducer page when you install the transducer in the SU90 user interface. |
|
|
3 |
Measure the physical location of the global positioning system (GPS) antenna.
There are two GPS antennas. Both are placed on the main mast, one on each side, each two meters from the mast. The mast is located on the top of the bridge, aft of origin. We will measure the coordinates to the port antenna.
NoteIn this context, the GPS antenna is regarded as the sensor.
|
a |
Draw a vertical line from the sensor and down. |
|
b |
Measure the vertical distance from the waterline and up to the sensor.
This is the Z value. The value is negative because the sensor is located over the origin.
|
|
c |
Measure the horizontal distance in parallel with the X axis from the origin to the vertical line.
This is the X value. The value is negative because the sensor is located behind the origin.
|
|
d |
Measure the horizontal distance in parallel with the Y axis from the origin to the sensor.
The sensor is on the port side of the centre line while the origin is located on the starboard side. This is the Y value. The value is negative because the sensor is located on the port side of the origin.
|
|
e |
Type the values you have found for X, Y and Z into the Sensor Installation page when you install the sensor in the SU90 user interface. |
|
|
4 |
Measure the physical location of the motion reference unit (MRU).
The motion reference unit is located next to the sonar hull unit. Both are placed on the vessel’s centre line and close to the bow.
|
a |
Draw a vertical line from the sensor and up. |
|
b |
Measure the vertical distance from the waterline and down to the sensor.
This is the Z value. The value is positive because the sensor is located under the origin.
|
|
c |
Measure the horizontal distance in parallel with the X axis from the origin to the vertical line.
This is the X value. The value is positive because the sensor is located in front of the origin.
|
|
d |
Measure the horizontal distance in parallel with the Y axis from the origin to the centre line.
The sensor is on the centre line, but the origin is located on the starboard side. This is the Y value. The value is negative because the sensor is located on the port side of the origin.
|
|
e |
Type the values you have found for X, Y and Z into the Sensor Installation page when you install the sensor in the SU90 user interface. |
|