Furuno DS-80 - Manual (Page 12)

4
REMARKS ON USAGE
Remarks on Usage
The DS-80 measures ship’s speed by
detecting the Doppler shift frequency of the
echo reflected by a watermass (water layer
containing plankton and other micro-
organisms) located within the measuring
area, which is usually about 2 m. In some
instances, however, no signal is returned
because of too few plankton in the sensing
depths. This phenomenon can occur in
particular areas in particular seasons. The
probable cause is the plankton are lying in
deep water because an ice-melted cold
water mass covers the sea surface. Similar
cases may also occur in a freshwater lake.
Under these circumstances the DS-80 will
not show the correct ship’s speed.
Conditions Affecting the
Accuracy
(with ref to IMO A.824/3.3)
The Doppler speed log DS-80 is designed for
reliable and accurate performance through
FURUNO’s long experience and advanced
technology. It operates on the best choice of
system frequency and power output. As far as
the sonic energy is used, the performance
(accuracy) may be reduced or even lost
under:
•
rough weather (may be sea state 6 or
severer)
•
improper location of sensor, e.g., too close
to the propeller, thrusters, drain tubes, echo
sounder transducer
•
depth under the keel if less than 3 m
The accuracy will not be affected by:
•
- water temperature (sound velocity)
•
salinity
•
pitch/roll ±10°
Beware of Transducer Location
The transducer may be damaged if it hits
the dry dock blocks. Take the following
measures to prevent damage to the
transducer.
1. Before delivering the ship, draw up a
suitable docking plan taking into
account the dimensions and location of
the transducer. Store the plans onboard
the ship.
2. Place the dry dock blocks according to
the plan.
3. Have a diver check the position
between the transducer and the blocks
before removing the water. Confirm that
the transducer will not touch the blocks.