JRC JLN-550 Instruction Manual page 30

In this case, because measuring of the ground speed becomes impossible, it sometimes changes to
the water speed indication.
It sometimes changes to the ground speed indication by accident when the fish school of the very
big reflection signal and a plankton layer are continuing within the depth of water 250m even if the
depth of water from hull bottom is more than 250m. It is changed to the forced WT mode, and used
in such a case.
BT (the forced BT mode)
•
It is used when obviously the depth of water from hull bottom always becomes stable under 250m
and wants a ground speed indicated.
It turns on a BT lamp, and a ground speed is indicated when the depth of water from hull bottom
is in the range of about 2 - 250m.
When the depth of water from hull bottom is about more than 250m, a BT lamp is made to go on
and off, and switching of the mode is required. In this case, former ground speed value is held and
indicated.
Even if the depth of water from hull bottom is more than 2m, measuring of the ground speed
becomes impossible during coming alongside in the case such as the mud that the sea bottom
quality absorbs a sound wave to. In this case, a BT lamp is made to go on and off, and former
ground speed value is held and indicated.
The sound wave of the measuring beam is shut out when the bubble that appeared on the part of
the bow at the time of the stormy weather, reaches to the transducer of hull. A ground speed can't
be sometimes measured under even 250m in such a case.
And, even if the depth of water from hull bottom is under 250m, some of the receiving signals
inside the measuring beam may decrease too much, and measuring of the ground speed becomes
impossible in the sea area whose seabed inclination is big, and the ups and downs. In this case, a
BT lamp is made to go on and off, and former ground speed value is held and indicated.
Both of the ground speed and the water speed are always outputted to the external devices
regardless of the setup of this mode.
• WT (the forced WT mode)
It sometimes changes to the ground speed indication by accident when the fish school of the very
big reflection signal and a plankton layer are continuing within the depth of water 250m even if the
depth of water from hull bottom is more than 250m. It is used when it isn't based on such a case and
the depth of water and it always wants a water speed indicated
When the depth of water from hull bottom is under 3m, a WT lamp is made to go on and off, and
the value of the former ground speed is held and indicated.
An error may arise in the value of water speed when the bubble that appeared on the part of the
bow at the time of the stormy weather reaches it to the transducer of hull.
Both of the ground speed and the water speed are always outputted to the external devices
regardless of the setup of this mode.
20 4. Operation