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Use of ships radar for improvement of
navigation in rough sea condition
Denis Akmaykin, Dmitry Khomenko
Annotation: The article describes creating of hardware and
software module to prevent accident situations at sea. The
module detects length and speed of sea waves by ships radar,
and recommends safe course for navigators.
Key worlds: sea state, safety of navigation, wave diagram,
radar, differentiating circuits, fast time constant circuit,
Electronic Chart Display and Information System (ECDIS).
T
he sea state is usually one of the determinative factors for
the deep-sea vessels. Any vessel in relation to the storm
level increases the risk of accidents in the following
circumstances: rolling, pitching, broaching, slamming, washing
deck with large mass of sea water etc. These factors also affect
the stability and maneuverability of the vessel. All the above
mentioned factors shall be taken into account when navigating
in poor weather conditions.
The serious threat for the vessel caught by broaching may
represent maneuvering in heavy seas at one of the following
cases may cause the collision situation i.e.:
considerable change or loss of the crossbeam stability
when passing by the crest of the wave close to the middle of
the ship. The most dangerous in this connection is the
movement of the vessel in the wave, the length and speed of
which are close to the length and speed of the vessel when the
vessel with the low level of stability can stay in these
circumstances for longer period of time than the period
necessary for inclination from the vertical angle position to the
dangerous angle and to capsizing;
main resonance or parametric resonance of rolling, when
τ = То or τ = То/2, where τ – seeming period of wave
approaching , То – rolling period;
wave capture, loss of control, spontaneous turn alongside
the wave is broaching. The most dangerous case is lock-in on
the front slope of the wave when the velocity of the wave is
more than the ship’s speed. Vessels of 60 m long and less are
subject to broaching.
To facilitate ships control in heavy seas the soviet scientists
worked out the diagram able to select optimal course and
speed in case of rough weather. This diagram was drawn up by
V.
Vlasov,
S.
Blagoveshenckiy,
L.
Nogid,
U. Remez [1].
Later on, Remez universal diagram for deep-water got the
greatest distribution on conformability with good seamanship.
In practical application deep-water means a depth over than
half of the wave length.
The universal diagram of the wave for deep-waters consists
of the upper and lower parts (fig. 1).
The upper part of vertical axis is a wave length λ
calibrated, horizontal axis is Vcosq calibrated. Where V –
ships speed, kts; q - relative bearing of wave direction, deg.
The lower right part of the diagram shows the movement of
the vessel abeam coming wave or waves oncoming to the
vessel. The middle vertical line corresponds to the course
alongside the wave at any ship’s speed. The lower left part of
the diagram shows the movement of the vessel on the
following sea or waves against ship quarters, including
appropriate data: negative Vcosq (90<q<180).
The upper part of the diagram contains the beam of curves,
each of them is built for the definite meaning of seeming
period of wave τ. The curves are marked accordingly.
When the vessel is not under way or moving alongside the
waves, the seeming period of waves τ coincides with true
period (period relative to the fixed object) τо. This intersection
of vertical axis ordinate and curve is relevant to the seeming
period of length of wave λ, true period of which is equal τо.
For example τо = 8s λ=100m, τо = 12s λ = 225m etc. In
case of crest of the wave the seeming period of wave to be less
than true period, in case of following sea, unless vessel is not
overtaking the wave.
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Fig. 1. The Remez universal diagram for deepwater: λ — wave length;
V — ships velocity; q — relative bearing of wave direction.
On the following sea, projection of ships speed on
direction of distribution of waves Vcosq match with waves
speed, which is equal to 2,43√λ kt, thus seeming period of
wave towards eternity, look like saddled wave. In this case on
following sea ship is seemed to be fixed relatively to the
system of waves. The vessel will seem drifting to the observer.
The dotted curve τ = ∞ corresponds to the case mentioned
above.
The lower part of diagram includes concentric semi
circumferences with center, located at the begining of
coordinates of diagram and the bunch of rays coming from the
center. Each semi circumference corresponds to defined value
of speed V (kt). Each ray corresponds to the definite relative
bearing q. The right side of the lower part of diagram
corresponds to the counter sea, the left side to the following
sea.
So far as during plotting the diagram, it is accepted that the
waves have starboard to port direction, ship’s speed is directed
from the center to periphery of her lower part along ray,
corresponding to the value of relative q. The appointed
combination of speed and relative bearing corresponds to the
point in the lower part of diagram as an end of speed’s vector.
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The lower part of diagram gives ability to find graphically
value of Vcosq with given combination of V & q, as well to
solve the opposite task of detection of all values V & q,
responding the given Vcosq.
Storm diagram made up by V. Lipis, D. Rondrikov, V.
Remez is a universal diagram, as well as other information
contained in guides, can essentially help a navigator to choose
optimal solution. The Remez diagram also allows to define
unfavorable combination of speed and relative bearing of
waves, so-called resonance zone, that give a mariner
opportunity to make a decision in selection of the method of
behavior in the stormy weather.
However, practical application of storm diagrams is not
used out on vessels due to complete calculation and, because
of the height and direction of waves which are visually
determined by navigators. During navigation in bad weather
captain should avoid proceeding alongside the wave, reduce
rolling to minimum, trying while maneuvering to shorten the
time of influence of waves in hazardous position.
Nowadays satellite microwave devices with different
ranges, waves lengths are used for global monitoring of wind
speed and direction above water surface, sea state
characteristics and charting them. The above mentioned
devices also measure ice cover, instrumentation of atmosphere
moisture, content and water reserve above the ocean,
definition of precipitation zones and their intensity [2].
However such methods of detection of sea surface
characteristics are not used in practical application on board.
Quick receiving of similar charts requires a long time, when
the chart become out of date or in case of satellite support it is
required extra costs and a lot of additional time for the
information processing.
For improvement safety at sea, in our opinion the height
and direction of sea waves is possible to detect with the help of
ships radar assistance. Several clutters occur during radar
working. Considerable influence on radar work render the
clutters, produced by echo from waves, rain, clouds etc. Such
echoes cause long duration clutters, overloading amplifier of
receiver and almost excluding target monitoring on the screen.
To prevent long range clutters, radar receivers are supplied
with the differentiating circuits between detector exit and first
cascade entrance of amplifier, sometimes they call fast time
constant circuits [3].
The use of the unfiltered signal, at once after the output of
detector we can judge about meteorological characteristics
around the ship by spectrum of the signal received. Further
signal processing allows to single out separate kinds of these
characteristics, such as sea roughness at real time.
All ocean-going vessels are equipped with Electronic Chart
Display and Information System (ECDIS), which are used in
navigation. Modern ECDIS has variety of innovative
opportunities, one of them is a position prediction ability,
during maneuvering (fig. 2).
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Fig. 2. Mode forecasting maneuver in Electronic Chart Display and
Information System company Kelvin Hughes.
Knowing the parameters of the sea, direction and the sped
of the ship it is possible to create the hardware and software
module for ECDIC. This module will be able to track the
vessel’s movement relatively the wave and to calculate the
optimal course under these parameters of wave. In case of
necessity it notifies the navigator about the dangerous courses
and speeds which are close to resonance. The calculation of
the optimal course relatively the waves allow to save fuel and
time spent for the voyage. In complicated meteorological
conditions this system may save the ships and crews lives.
Reference:
[1] S.I. Demin, E.I. Zhukov and others. Ships control; Edited by Snopkov
V.I. – M.: Transport, 1991. – 395с.
[2] Yu.A. Kravtsov, M.I. Mityagina A.N. Chyuryumov. Method of nonresonance dispersion of electro-magnetic waves on the sea surface.
Dispersion by steep-to sharp shape of waves// University proceedings.
Radiophysic. vol XLII, #3, 204-254, 1999
[3] A.M. Bayroshevskiy Ships radar stations; Morskoy transport
publishers, - Leningrad, 1988. – 348p.
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