Vessel coordinate system
When you have several different sensors and transducers on your vessel, and you wish each of them to provide accurate data,
you need to know their relative physical positions. On larger vessels, each sensor may be located far away from each other.
The antenna of a position sensor is typically mounted high above the superstructure, while a motion sensor is located close
to the vessel’s centre of gravity. Both of these are physically positioned far away from the transducer on a depth sensor,
which may be located closer to the bow. Very often, the information from one sensor depends on data from an other. It is then important that the relevant measurements
are compensated for these relative distances.
In order to establish a system to measure the relative distance between sensors, a virtual coordinate system is established.
This coordinate system uses three vectors; X, Y and Z. In the MS70 system, the same vessel coordinate system is used to define the transducer installation angles.
The installation angles are recorded on the MS70 Transducer Offsets page in the Instrument Offsets dialog box to create the correct echo presentation independent of the transducer location and installation angles. The Instrument Offsets dialog box is opened from the Install button on the Active menu.
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A |
X-axis This is the main axis in the vessel’s forward (alongship) direction. Positive values are forward relative to the origin.
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B |
Y-axis This is the transverse (athwartships) direction. Positive values are toward starboard relative to the origin.
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Z-axis This is the vertical direction in parallel with the mast. Positive values are down relative to the origin.
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Origo The origo is the common reference point where all three axis in the vessel coordinate system meet. All the physical locations
of the sensors are referenced to the reference point.
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Installation angles
If you look at the transducer, you can see how it rotates on each axis in the vessel coordinate system.
Keep in mind that in its default position (all axis set to 0 (zero)) the transducer points straight down with the orientation
mark (arrow) pointing forward. This default position must always be used as reference for rotation adjustments.
NoteIn order to establish the correct installation angles, you must do a virtual exercise. It is very important that you define
the three values in the correct order: first X, then Y and finally Z.
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Place the transducer in its virtual start position with the face straight down, and with the 0–mark pointing forward. |
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If necessary, rotate the transducer on the X-axis. If you wish to point your transducer forward for trawl or navigational applications, the value for X shall be 0 (zero), and
the 0–mark must be up.
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Rotate the transducer along the Y-axis. A positive value will "tilt" the transducer face up. Keep in mind that the 0–mark shall still be up.
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Rotate the transducer along the Z-axis. The 0–mark shall be up, and the value for Z (positive towards starboard and negative towards port) will define the direction.
If you wish to point your transducer forward for trawl or navigational applications, the value for Z shall be 0 (zero).
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Changing the installation angles
The installation angles are recorded on the MS70 Transducer Offsets page in the Instrument Offsets dialog box to create the correct echo presentation independent of the transducer location and installation angles. The Instrument Offsets dialog box is opened from the Install button on the Active menu. This must be done once the transducer has been installed, and the MS70 has been started. You will normally only need to do this once.

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This installation angle is defined using the Rotation around Y value. Keep in mind the default "start location" of the transducer; all rotation angles set to 0 (zero) means that the transducer
face is horizontal pointing straight down with the orientation mark (arrow) pointing forward. Lifting the transducer to the
requested angle will always require a positive rotation around the Y-axis.
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This installation angle is defined using the Rotation around Z value. Turning the transducer sideways will always require a positive (or negative) rotation around the Z-axis. A positive Z-axis value will turn the transducer towards port, while a negative value will turn it towards starboard.
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You will only need to adjust the rotation around the X-axis if the transducer is mounted with the orientation mark (arrow)
pointing in the wrong direction, or if it necessary to adjust for an inaccurate installation.
Example 1
The transducer shall be pointed approximately 90 degrees towards starboard with the indicator arrow pointing up. To set the angles correctly, observe this exercise. Use your cellphone to visualize the transducer movements.
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Start with the transducer in its default position: the transducer face is horizontal facing down, and the indicator arrow
is pointing straight forward. |
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If the transducer is properly installed without unintentional skew, the Rotation around X can also be set to 0 (Zero). |
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Lift the front end of the transducer up, so that the indicator arrow moves up. This is a Rotation around Y. |
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Proceed until the requested angle has been reached. Example: If a 15 degrees Y angle is requested, the Rotation around Y must be set to 75 degrees (that is the angle from the default position).
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From this raised position, turn the transducer towards starboard. The indicator arrow is still pointing up. This is a Rotation around Z. |
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Proceed until the requested angle has been reached. Example: If a 90 degrees Z angle is requested, the Rotation around Z must be set to 90 degrees (that is the angle from the forward position).
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Example 2
The transducer shall be pointed approximately -90 degrees towards port (or 270 degrees towards starboard, which puts you in
the same direction) with the indicator arrow pointing up. To set the angles correctly, observe this exercise. Use your cellphone to visualize the transducer movements.
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1 |
Start with the transducer in its default position: the transducer face is horizontal facing down, and the indicator arrow
is pointing straight forward. |
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2 |
If the transducer is properly installed without unintentional skew, the Rotation around X can also be set to 0 (Zero). |
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Lift the front end of the transducer up, so that the indicator arrow moves up. This is a Rotation around Y. |
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Proceed until the requested angle has been reached. Example: If a 20 degrees Y angle is requested, the Rotation around Y must be set to 70 degrees (that is the angle from the default position).
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From this raised position, turn the transducer towards port. The indicator arrow is still pointing up. This is a Rotation around Z. |
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Proceed until the requested angle has been reached. Example: If a -100 degrees Z angle is requested, the Rotation around Z must be set to -100 degrees (that is the angle from the forward position). Setting it to +260 degrees will also work.
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