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Grounding Point.
This should always be submerged !
When mounting the sensor in a ship’s hull or on another platform, make sure the grounding point always
touches the water.
8.2.3 Ship movements
Try to avoid mounting the Signature sensor too close to the bow or to the stern. Instead, the best areas are
toward the middle of the ship. There are two reasons to pick an area toward the middle. First, the vertical
motion due to pitch and roll is minimal toward the middle. Second, the ship-induced flow field has stronger
asymmetries toward the bow and stern. These asymmetries will reduce the accuracy of the velocity data
close to the hull and are best kept to a minimum. Ship induced motion is usually a bigger problem the larger
the ship, the relative water depth is smaller, and the ship is more bulky (less "classic" hull structure). It is
usually not a significant problem on small vessels or for Signature Sensors mounted over the side.
The tilt angle of the installation should be as small as possible because a level sensor head makes it easier
to interpret and analyse the velocity data. However, a few degrees of tilt does not make a great difference in
the accuracy of the horizontal velocity data
8.2.4 Ship generated flow fields
All ships generate their own flow field. The magnitude of this field is a function of the ship size, shape, ship
speed, and the water depth. It is weaker away from the hull than it is close to the hull and it will be weaker
on the side of the ship than it is directly below the hull. The magnitude of the flow field can be analysed by
looking for persistent vertical gradients in the velocity data.
a) The flow field is strongest close to the hull and will usually "pull the water along with the ship". As a result,
the sign of the velocity gradient will remain constant and it will not change direction as the ship moves in the
opposite direction. If the gradient remains constant, regardless of the direction of the ship motion, it is not a
part of true current regime, but an artefact of the ship induced flow field.
b) When the Signature sensor is mounted close to the bow or to the stern, it will show a net vertical velocity
close to the hull. If the vertical velocity has a strong gradient (i.e. it is not constant with the water depth), it is
usually a result of the motion.
