Outline of "Investigation for Navigation Safety System on Tankers"
Kenji Mishima
PASCO Corporation

1 Introduction
In keeping pace with the expansion of international ocean trade, oil tankers
and other ocean vessels are increasing both in size and in number,aggravating congestion of marine traffic. Accidents involving these large
ships such as collisions and stranding, and the resulting spills of crude oiland fuel can cause large-scale marine pollution and therefore serious
environmental, economic, and social problems. There is a growing demand,
therefore, for effective measures to prevent accidents involving large ocean
vessels including large tankers.
In this project, a study was conducted to evaluate the feasibility of anavigation safety support information system for tankers, a system whichenables a ship to determine its own and nearby ships' positions accurately
and exchange information by making effective use of a number of
information technologies including , by The Petroleum Association of Japan .
(1) Electronic chart information technology,(2) Global positioning system (GPS)technology,(3) Geographic information technology, and(4) Digital communications technology.
An outline about the possibility is described below .

2 Fact-finding Survey of Marine Accidents
Accident reports and shipping companies were surveyed to collectinformation on the causes of past marine accidents. The survey revealed thatthe causes of marine accidents such as collisions due to dense fog, squalls, orobstructive weather conditions and strandings due to discrepancy between
charts and actual ship positions, except for accidents caused by humancarelessness, can be categorized as follows (see Fig. l):(1) Inadequacy of communication(2) Inaccuracy of information(3) Difficulty of processing a large amount of information quickly
These collisions and strandings can be prevented by taking
appropriate preventive measures. What needs to be done, therefore, is topropose a system capable of solving these problems.

3 Survey of Related Technologies
Technologies needed to build an effective safety system include the following:(1) For better communication Digital communications technology to improve
communication(2) For more accurate information Electronic chart information technology
Global positioning system technology(3) For faster processing of more information Geographic informationtechnology

4 Outline of the System
In proceeding with system design taking into consideration the causes ofaccidents and available technologies that can be used to prevent such
accidents, it is necessary not only to coordinate with international trends
toward standardization and unification but also to seek operational andeconomical efficiency.
These related technologies include the following:(1) IBS (Integrated Bridge System)(2) GPS (Global Positioning System)(3) ECDIS (Electronic Chart Display Information System)(4) DSC (Digital Selective Calling)(5) GMDSS (Global Maritime Distress and Safety System)(6) VTS (Vessel Traffic Service)

The navigation safety support information system for tankers,
therefore, uses the technologies to collect, integrate, and display various
information, including positional information from GPS, information fromsatellite communications systems and automated communications systems
Such as DSC (Digital Selective Calling),and electronic chart information.
The navigation safety support information system enables the shorebase station to keep track of the conditions in the service area on the basis of
information received from individual ships. By monitoring transmissions
from other ships, each ship can obtain the same information that the shorebase station receives.
Information on other ships monitored by each ship can be limited to
information on nearby ships, instead of all ships in the service area. Thus,
the shore base station is responsible for controlling the timing oftransmissions in its service area to prevent interference and does not have toretransmit received information to ships in the service area.
The key to successful implementation of such a system is thecommunications method to be used.

4-1 Functions as Viewed from the Shore Base Station(1) A ship enters the service area of the system. The shore base station has
been transmitting signals requesting the ship that has entered the service
area to register with the station.
Automatically alerted that it has entered the service area, the ship
sends to the base station relevant information, including the type ofmessage, identification, and the GPS-determined position, course, andspeed of the ship (registration of entrance).
After completing the registration as requested, the base station
assigns a zone and a time slot to the ship.
The assignment of the time slot involves specifying the time at which
each ship is to transmit its information. The purpose of time slot
assignment is to make sure that information from a great number of shipsis transmitted in turn without interference.

Fig.2

Enter to Service Zone (Getting Information of Ships)

(2) In the service area, the base station requests each ship to send its
information according to the assigned time slot (request for scheduledreporting) .
Ships that have been requested to send such information transmit tothe base station information on themselves, including information on thetype of message, identification, ship location, course, and speed.
The above process proceeds automatically.

Fig.3

In a Service Zone

(3) Any ship desirous of leaving the service area requests the shore basestation for a registration of exit.
In response to this request, the shore base station acknowledges
receipt of the request and terminates its service by transmitting
appropriate signals.

Fig.4

Exit from Service Zone

4-2 Functions as Viewed from Ships(4) A ship enters the service area of the system. Automatically alerted that it
has entered the service area, the ship sends to the base station relevant
information, including the type of message, identification, and the GPS
determined position, course, and speed of the ship (registration ofentrance).
After completing the registration as requested, the base station
assigns a zone and a time slot to the ship.

Fig.5

Entrance to Service Zone

(Giving Information of Ship's own)

(5) Each ship monitors transmissions that other ships transmit to the shorebase station according to the assigned time slots. Information thus
obtained is displayed on the ship's monitor, along with electronic charts,
GPS-determined position of the ship, and other navigation support
information. Thus, each ship can acquire the same information that otherships send to the shore base station.

Fig.6

The Times of Report on Schedule(Interception to Information of Another Ships)

(6) Any ship desirous of leaving the service area requests the shore basestation for a registration of exit.

Fig.7

Exit from Service Zone

4-3 Inter ship Communication on International Waters(7) On international waters where ship trafficis not heavy, ships are allowed
to communicate with each other without heeding the possibility ofinterference.

Fig.8 Out of the Service Zone
(Exchange Each Information of Ships)

5 Prototype Development and Performance Testing
A prototype system has been developed according to the design concept
Outlined above. Figs. 9 to 2 1 show examples of simulation screens of thesystem.
Fig. 9The on-ship system accumulates information on other ships bymonitoring their transmissions to the base station.

Fig. 10 The system issues a collision alarm if the ship is on a collisioncourse with another ship.
Fig. 11 The system issues a stranding alarm if the system decides, on thebasis of data on shallows and sunken rocks shown on electroniccharts, that the ship might be stranded. The white dots show thelocations of sunken rocks.
Fig. 12 Following a collision alarm, the oncoming ship on a collision courseis identified and called up.
Fig. 13 The selective call in Fig. 12 has been answered.

6. Conclusions
In the simulations carried out using the prototype system, calling up aselected ship took 25 seconds. In a test of area calling, calling up 5 ships took
12.5 seconds. The maximum response time in the case of selective callingsoon after the start of scheduled communications according to the DSC
controller's communications schedule was 12.5 seconds. This is because
selective calling is carried out after completion of scheduled communications.
Concerning response time in scheduled communications, sincescheduled communications with one ship takes 2.5 seconds, the responsetime for 250 ships is 625 seconds (about 10 minutes).
Ship symbols shown on the system display are updated every I O
minutes because positional information for each ship is obtained fromscheduled communications. Since scheduled communications can take up to
1 O minutes, inter ship communications may have to wait for up to I O
minutes. Therefore, if a registration of entrance is made during scheduled
communications, contention may result.
As the transmission rate of the existing system is 1 200 baud,scheduled communications for one ship takes 2.5 Seconds. If thetransmission rate is raised to 9600 baud, the time required for scheduled
communications for 250 ships will be reduced to 10 minutes to 2 minutes, afeasible range. This will decrease the waiting time in selective calling,helping to prevent the occurrence of contention. It also helps to reduce
interference with communications for registration of entrance and scheduledcommunications.
In this study, only one radio channel was used for communications.
In order to raise the transmission rate and prevent radio interference, it isnecessary to use two channels instead of only one. Allocating one channel toscheduled communications between the base station and ship stations andthe other to emergency communications between ships (selective calling,area calling) and registration of entrance will greatly contribute toprevention of interference and contention.
By investigating a shipwreck accident, it was possible to investigate
to process a lot of information for which it is difficult to communicate will
mutually it was improper and quickness of it and that these which aredifficult were cause. It found that these were a factor. Therefore, thestranding accident can be prevented in one's own ship's having correct
information. Also, the collision accident can be prevented in specifying
shipping in font in sharing the correct information of the other ship by eachshipping and summoning it individually and confirming mutual intention.
This system made it a system concretely. As for this system, the effective
thing could be confirmed to prevent from the stranding accident and thecollision accident of the large-sized shipping such as the tankers. And thesystem of this study, that all the ships are equipped with this system
becomes a presupposition. Therefore, the realization of this system in theearly stage is waited for.