International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 2
Number 1
March 2008
51
Study on One Mile SART
S. Hayashi
Tokyo University of Marine Science and Technology, Tokyo, Japan
M. Ogawa
Japan Ship-Machinery Quality Control Association, Tokyo, Japan
M. Ide
M. O. Marine Consulting Ltd., Tokyo, Japan
ABSTRACT: From a point that should be improved further in present SART (Search and Rescue Radar
Transponder), the size, the number, and the cost were enumerated. Some types of SART developed to solve
them in Japan are introduced in this paper. That is automatically operating SART, circular polarization SART
and so on. In the process, it was clarified that circular polarization is effective. In addition, One Mile SART
using circular polarization was mentioned. It is SART miniaturized instead of limiting the function, because
all crews and passengers can always carry the small and light SART. The parts were made for trial purposes
and the performance was confirmed.
1 INTRODUCTION
After it is completely equipped with GMDSS
(Global Maritime Distress and Safety System) by the
SOLAS (the Safety of Life at Sea) agreement by
IMO (International Maritime Organization), the
accident ship came to be rescued effectively. At the
same time, however, some problems and points that
should be improved are understood. In this paper,
SART of GMDSS was examined.
The main problems in use are thought the size
and the number of installations. To solve them,
a necessary performance requirement was limited
and the miniaturization was tried.
2 PRESENT SART
2.1 Externals specification and cost
SART was developed to detect and to do homing for
the lifeboat with the radar of the search ship. It is
provided to one of GMDSS as equipment goods of
the ship and the lifeboat. Though the height of the
main body is about 30–40 cm, when using it, it
installs in the ceiling of the lifeboat or in the stick of
the attachment, and 1m or more in height above sea
level is secured. Weight is about 1–4 kg. A price on
the market is about 900 US$, and it costs 500 US$
the battery kit that should be exchange every 3–4
years.
2.2 Performance requirement
The main of the performance requirements provided
by the SOLAS agreement is listed in Table 1.
Table 1. The main performance requirement for present SART
Temperature range
(in operation)
–20 –+55 Celsius degree
Operation time
After stand-by 96 hours,
continuous response for 8 hours
Height of antenna above
sea level
1m or more
Reception sensitivity
below –50 dBm
Radiation electric power
400mW (+26dBm) or more
frequency
9200–9500 MHz
polarization
horizontal
Weight
1– 4 kg
3 IMPOROVED SART
At first of the SOLAS agreement enforcement
concerning GMDSS, SART was one (Passenger boat
52
etc. are 2) in each ship. It is fewer than the number
of crew and passenger or the number of lifeboats.
This is thought to be a result of considering an
economic side very much. When actually leaving
from the mother ship, it is necessary to carry SART.
It is, however, not easy to go to installation place and
board the lifeboat by carrying it in the dark night or
at rough sea. There is a possibility of dropping it to
the sea, too. In Japan, the development and study are
done to solve these problems. Three kinds of SART,
that is, life raft installation type, dropping type, life
jacket installation type are developed and the result is
achieved.
3.1 Life raft equipment type SART
It is a type to install SART in the ceiling part of an
automatic restoration life raft beforehand. It is not an
obstacle even if the life raft is usually folded and put
it in the container. When the container is dropped to
the sea and the life raft expands, the switch of SART
is automatically pulled out and operation begins.
Figure 1 shows the photograph of the life raft
equipment SART.
Fig. 1. Life raft equipment SART
Fig. 2. Dropping type SART
3.2 Dropping type SART
It is SART of the type in which the fold stick of
about 2m in total length previously installed only the
antenna. It is folded compactly, and the stick
expands automatically when drop it, the floating
body expands, and SART also begins operating.
The main body of SART and battery are installed
from the center of the stick a little below with the
floating body. The weight is attached on the
opposite side of the stick, and the height of about
1.5m is maintained on the sea surface. The
photograph is shown in Figure 2. This is installed to
the buoy for the examination.
3.3 Life jacket installation type SART
Life jacket installation type SART (called life jacket
SART in this paper) was developed using circular
polarization antenna based on the obtained result by
above 3.1 and 3.2. One example is shown in Figure 3.
In this type, the case where person falls in water
is assumed. Therefore, some contents in Table 1 are
over specification for usual condition of life jacket
installation SART. The suitable specification is
shown in Table 2.
Fig. 3. Life jacket SART
Table 2. The Specification of the life jacket SART
Temperature range
(in operation)
-1 ÷ +55 Celsius degree
Operation time
After stand-by 24 hours,
continuous response for 4 hours
Height of antenna
above sea level
20cm or more
Reception sensitivity
below -50 dBm
Radiation electric
power
400mW (+26dBm) or more
frequency
9200-9500 MHz
polarization
Circular
weight
180g
Fig. 4. SART for life jacket installation
53
When these are decided, the situation of the
occurrences of the shipwreck in the near shore
waters and the accident of falling in the sea are
researched, furthermore, the relation between tempe-
rature of seawater and time that person who fall in
the sea can live, was considered. The main change
point is a use temperature and continuous operation
time. Though the height of the antenna is not
especially decided, the shoulder or the top of helmet
of man who floats on the sea wearing the life jacket
are assumed.
As the result, the use of a small general-purpose
battery became possible, and the main body became
the size of 8 mm videocassette tape. The prototype
is shown in Figure 4.
4 COMPARISON BETWEEN PRESENT SART
AND CIRCULAR POLARIZATION SART
When these had been designed, in the process of
examining the miniaturization of the antenna and the
connection of the main body of SART and the
antenna about the simplification, it has been
understood that the use of circular polarization has
advantage. The antenna of SART is provided the
horizontal polarization according to ship’s radar.
SART, however, doesn’t necessarily keep the pola-
rization, because big wave motion is generated at
sea. It is thought that there is attenuation based on
the rotation of the polarization by the reflection on
the surface of big wave. Therefore, the difference in
the effect is almost nothing between the horizontal
polarization and the circular polarization in rough
wave.
The polarization plane rotates in the circular
polarization. Therefore, because null that originates
in interference by the direct wave and the reflection
wave becomes small, it is possible to receive it with
stability. Moreover, differing height pattern becomes
an effect, and the effective range expands.
In the examination in the water tank and the sea,
circular polarization often gave strong receiving
signal for the horizontal polarization.
Figure 5 shows the one example when sea state is
calm. The lower line (SARTradar) in the graph is
theoretical value of horizontal polarization and the
block dots are received signal from circular
polarization SART. The value that is stronger than
the theoretical value of horizontal polarization is
indicated, and it is also understood that detection
distance has expanded as a experimental result.
In the use of circular polarization, the antenna can
be miniaturized. Furthermore, there is an advantage
with an easy separation of the distance of the main
body and the antenna because of connect possible by
the semi- rigid cable. It means the antenna can be
miniaturized and the design has flexibility for
installation.
Figure 6 shows the result when sea state is rough.
Fig. 5. Theoretical value of horizontal polarization and
observed value of circular polarization
Fig. 6. Signal strength that radar received from SART in wave
height 2 – 3 m
The maximum value of the SART signal of
circular polarization and that of horizontal polariza-
tion in each observation point were compared, and
the difference is -0.8 to +5.6 dB. The value
numerically increases, when the signal of circular
polarization is stronger. Therefore, the signal of
circular polarization is stronger than or equivalent to
the horizontal polarization
Because of the difference of heights is not
constant at each observation point, each observation
data cannot be compared in same height pattern,
however, it was confirmed that SART of circular
polarization was no inferior comparing with
horizontal polarization.
5 ONE MILE SART
Furthermore, the authors aimed at the development
of less expensive and smaller SART based on these
results. To reduce the size to always carry it, and to
54
reduce the cost for all crews and passengers it is our
ideal purpose. SART consists an antenna, a battery,
an oscillation module, a control module and the case.
It made the limitation of the effective range to about
one mile to reduce the battery so that the battery
might occupy most of weight. One mile is about
1/10 compared with SOLAS agreement SART. It is,
however, difficult to find person who floats on the
surface of the sea even by the distance of only
hundreds of meters with the unassisted eye. It is
thought that the effect of reflecting in radar is large
even if the distance is only as much as one mile.
This SART is called One Mile SART in this paper.
5.1 Specification
The specification at which One Mile SART aims
shows in Table 3.
Table 3. The Specification of One Mile SART
Because it was assumption that the survivor in the
sea was putting SART, the category temperature
range was assumed to be almost -1 - +30 Celsius
degree from the water temperature where person was
able to live and the body temperature.
The effective receive sensitivity and the effect
radiation electric power relate closely to the battery
capacity and weight, and they should be made a
minimum requirement. The theoretical value for
effective radiation electric power 10mW and the
height of the antenna 20 cm is shown in Figure 7
forthe examination. The radar height is 6.5 m as a
the examination. The radar height is 6.5 m as a small
patrol vessel or small fishing boat. When the
minimum receive sensitivity of a radar for the search
is assumed to be -80 dBm, it is understood to be able
to secure the distance one mile. The effective receive
sensitivity can be secured enough. When effective
range is 1nm, transmission power is enough in
10mW.
Fig. 7. The theoretical value of One Mile SART
The battery is consumed by the range of
frequency and the circuit becomes complex, too.
Because most of the radar actually used with the ship
was a catalog value 9410MHz ±30MHz, the
frequency limited to only having the minimum
content of the range here.
About weight, it aimed at the level of the cellular
phone or the penlight as extent that did not become
obstructive even if it always carried, it aimed at 100g
or less.
5.2 Examination of each component
SART consists of the antenna, the oscillation
module, the control circuit, the battery and the case
separately, as mentioned. The result of review of
each element to achieve the above-mentioned
specification will be presented. Total weight is
brought together, it becomes less than 100 g.
6 CONCLUSIONS
To solve problem of present SART, new SART
developed in Japan was introduced. In addition, the
examination that aimed at SART that each one was
able to carry at any time was done, and the
performance of the minimum requirement was
maintained and miniaturized. The performance was
confirmed and the weight became less than 100 g.
The authors will be going to put the improvement
and integration to practical use achieving it in
addition in the future, and to achieve a prompt
salvage.
REFERENCES
Japan Ship-Machinery Quality Control Association, 2001.3
Research and study report concerning Dropping type SART
Japan Ship-Machinery Quality Control Association, 2002.3
Research and study interim report concerning Life raft
installation type SART and miniaturization for Life jacket
installation type SART
Temperature range
(in operation)
Operation time
Height of antenna above
sea level
Reception sensitivity
Radiation electric power
frequency
polarization
weight