230
12 Radar Systems of Maritime Transport
Having determined the elements of total drift, it should be considered when input
a graphic plotting. It has been experimentally defined that if the observed landmark
is at a distance of up to 6 miles from the vessel, then the drift velocity is determined
with a mean-square error equal to ±0,15 knots. At the same time, the specification
of drift velocity every half an hour increases the reckoning accuracy by 4 ÷ 5 times.
5. Control of vessel position at anchor
ARPS capabilities are useful in other cases as well, for example, during anchorage
(anchor hold). For this, in is necessary to take 2–3 radar landmarks for auto-tracking,
record the control (reference) values of its bearings and distances and constantly
monitor its changing. Small multi-directional changes in these values indicate a
reliable hold. If there is a clear tendency in its change, then this is due to the presence of
drift at the anchor (Anchor dragging). For automatic control of the distance exceeding
the set limits, the sound signaling “distance of dangerous approach” or “guard zones”
can be used.
There are other methods of visual and instrumental orientation, providing continuous control of the movement and location of the vessel. The main advantage of visual
and instrumental orientation methods is that during navigation they do not require
the distraction of the navigator to work on the map, which provides the possibility
of continuous visual and radar observation of the surroundings. At the same time,
these methods must be rationally combined with conventional observational reckoning methods, their value lies in the fact that they provide fast, prompt and reliable
information on whether the ship is safe between observations.
The particularity of the visual–instrumental orientation methods is that their application requires more thorough than usual and deep study of forthcoming passage,
selection of characteristic landmarks and corresponding delineation of preliminary
plotting. Figure 12.20 shows one of the possible examples of preliminary plotting
of a ship passage in confined waters and the radar screen image when the vessel is
at point O, shown on the map. In the given example, four parallel index lines are
used, one of which serves as the fencing distance, and the VRC, which determines
the secant distance, which fixes the point of a turn.
6. Use of ARPS at divergence of vessels
A complete assessment of the situation is possible only by analyzing both primary
(raw/unprocessed target echoes) and secondary (vectors and digital data) information.
The analysis of the primary information for targets selection for acquisition is
carried out by an ocular estimate method of targets afterglow traces in the same way
as at manual radar plotting. First of all, critical (dangerous) and potentially critical
targets are selected for auto-tracking (AT).
Secondary information is used to assess the degree of danger of the situation.
During radar surveillance using ARPS, the navigator uses the following data to
assess the danger degree of approaching situation:
• location of the RM vector relative to own ship;
12 Radar Systems of Maritime Transport
Having determined the elements of total drift, it should be considered when input
a graphic plotting. It has been experimentally defined that if the observed landmark
is at a distance of up to 6 miles from the vessel, then the drift velocity is determined
with a mean-square error equal to ±0,15 knots. At the same time, the specification
of drift velocity every half an hour increases the reckoning accuracy by 4 ÷ 5 times.
5. Control of vessel position at anchor
ARPS capabilities are useful in other cases as well, for example, during anchorage
(anchor hold). For this, in is necessary to take 2–3 radar landmarks for auto-tracking,
record the control (reference) values of its bearings and distances and constantly
monitor its changing. Small multi-directional changes in these values indicate a
reliable hold. If there is a clear tendency in its change, then this is due to the presence of
drift at the anchor (Anchor dragging). For automatic control of the distance exceeding
the set limits, the sound signaling “distance of dangerous approach” or “guard zones”
can be used.
There are other methods of visual and instrumental orientation, providing continuous control of the movement and location of the vessel. The main advantage of visual
and instrumental orientation methods is that during navigation they do not require
the distraction of the navigator to work on the map, which provides the possibility
of continuous visual and radar observation of the surroundings. At the same time,
these methods must be rationally combined with conventional observational reckoning methods, their value lies in the fact that they provide fast, prompt and reliable
information on whether the ship is safe between observations.
The particularity of the visual–instrumental orientation methods is that their application requires more thorough than usual and deep study of forthcoming passage,
selection of characteristic landmarks and corresponding delineation of preliminary
plotting. Figure 12.20 shows one of the possible examples of preliminary plotting
of a ship passage in confined waters and the radar screen image when the vessel is
at point O, shown on the map. In the given example, four parallel index lines are
used, one of which serves as the fencing distance, and the VRC, which determines
the secant distance, which fixes the point of a turn.
6. Use of ARPS at divergence of vessels
A complete assessment of the situation is possible only by analyzing both primary
(raw/unprocessed target echoes) and secondary (vectors and digital data) information.
The analysis of the primary information for targets selection for acquisition is
carried out by an ocular estimate method of targets afterglow traces in the same way
as at manual radar plotting. First of all, critical (dangerous) and potentially critical
targets are selected for auto-tracking (AT).
Secondary information is used to assess the degree of danger of the situation.
During radar surveillance using ARPS, the navigator uses the following data to
assess the danger degree of approaching situation:
• location of the RM vector relative to own ship;