Ship’s position information used to be available only through the dynamic reports sent from ships, but with the development of modern navigation, especially with Automated Identification System (AIS) fitted on most ships, companies are now able to track real-time vessel positions by themselves or by employing third-party service providers. Like any other electronic devices, AIS is not always reliable. In the event of technical malfunction and loss of the AIS signal, ships may be required to present position records and track records to “prove” themselves out of political and commercial considerations.

I.    Four ways of ship positioning

Determining the accurate position of the ship is a basic task for every ship master or navigating officer and one of the most important ways of ensuring navigational safety. There are many methods by which they can get a fix of the ship’s position – while GPS remains the primary method, others are also used when electronic system fails or when in confined waters.

1.   Dead reckoning

Dead reckoning is a technique to deduce the ship’s position at a given moment by applying to a known position on the sea chart a series of vectors representing courses and speed. Two aids to navigation will be used here – compass and speed log indicating course and distance respectively. It is a rather basic method and is seldom used in modern navigation. Since it does not rely on any object visible or visual bearing, it can be used as an alternative to determine ship positions when GPS system fails.

2.   Landmark fix

A ship’s position can be determined here by getting the visual or radar bearing of lights, lighthouses, hills, islands, capes, and other landmarks and plotting the same on the chart. The advantage of this method is that a rather accurate result can be obtained in a quick and convenient way. However, once the landmark is mistakenly marked, the consequences can be detrimental. The method can be used when the ship is proceeding near the coast or into the port, or in narrow channels. It is also a way frequently used to determine compass error.

3.   Celestial fix using sextant

Position can be ascertained by taking sextant altitude of celestial bodies like the Sun, Moon, or stars. Even though this method does not rely on electronic equipment, it can be time consuming as it involves complicated calculations and it is only accurate in good weather conditions.

4.   Electronic navigational aids

Some early electronic equipment like LORAN, Decca, RDF (radio direction finding) are no longer in the market since GPS has been available to the public. The electronic position-fixing system on board ships nowadays is normally shipborne GPS equipment or the developing BeiDou Navigation Satellite System. Such systems provide accurate and real-time ship positions and are connected with radar, radio station and AIS for integrated navigation and improved safety.

II.    Loss of the AIS signal

The SOLAS Convention requires AIS is to be fitted on all ships of 300 gross tonnes and upwards engaged in international service, cargo ships of 500 gross tonnes and upwards not engaged on international voyages, and all passenger ships irrespective of size, effective as of 1 July 2008. While the connection of AIS and GPS terminals has made possible real-time positioning and tracking of ships, failure of any one of the two equipment will result in loss of dynamic information. Here are some situations where ships may go dark without AIS signals.

1.   Instable power supply

When both the main and the backup power source are down or at extremely low voltage, AIS devices will not be able to work or transmit signals. This is a frequent error and often the first step of troubleshooting.

2.   Loss of GPS signal

Technically, if a ship transiting a certain area cannot simultaneously receive signals of four geostationary satellites, GPS signals can be instable, but only for very short periods. Unless under hacker attack, GPS signals are not likely to be lost for over 24 hours.

3.   AIS devices overheat

The two AIS devices are often installed on the bridge in front of the window and when the ship transits in high-temperature areas, it’s likely that the systems crash due to overheat.

4.   Antenna problems

Antennas may break or fall off in severe weather or in rolling period, and the device may not be able to transmit or receive signals.

5.   Deliberate shutting down of the device

Seafarers may switch off the device if it is overheated or if the ship is at berth.

6.   Signal interference

It’s also possible that the AIS signal is interfered by unknown parties or is disturbed by other AIS signals when transiting waters with heavy traffic.

III.   Identifying ship’s positions when off the AIS grid

Most ocean-going ships are equipped with two sets of GPS devices, one integrated with the AIS. Sometimes, a ship’s real-time track record may be temporarily “lost” to companies and third parties, but regardless of the reasons behind it, the ship’s position information can always be retained by certain means.

1.   GPS log

Ship’s position information on previous voyages are normally not stored in the GPS devices on board, nor can they be exported. So, in practice, navigating officers would jot down the ship’s position as indicated by GPS at regular intervals – approximately every one hour in open seas and every half an hour in confined waters. Such records can be seen in various forms – a notebook, a journal or a stack of paper, but do not have much legal force as they are just draft records without master signature.

2.   ECDIS log

The ECDIS log on board ships can be divided into two types. One is very similar to the GPS log mentioned above, and another is the excel sheet of recent track records exported from the ECDIS. However, such sheets are not necessarily effective, as the name of the ship, the specification of ECDIS or any other identifying information are not included. But it is always feasible to record ship positions by using the ECDIS playback function and taking snapshots.

3.   Deck log

As one of the statutory documents that faithfully records production activities conducted on board ships, deck log serves as an importance source of information to be referred to. It details weather, sea state, course, speed, cargo particulars, oil water distribution, and other information noted down by officers-on-duty with confirmation by signatures. Masters are required to examine the document and sometimes companies may monitor the keeping of deck log.

IV.   Advice to Members

With the commercial and political context getting grim for the shipping industry, authorities have focused on monitoring shipping activities through track records. Therefore, it is strongly advised to maintain the proper functioning of AIS by regularly updating the inputs, running daily tests and ensuring a steady power supply. Cool the device down if the temperatures are high or get it covered from sunlight. Conduct self-inspection or transmit testing signals with the shore and passing ships so that problems can be detected in time, and reports to the company shall be made.

Given the comprehensiveness and authenticity of deck log, plus signatures by masters and navigating officers, deck log can be presented as evidence that is legally effective. Therefore, it is important to keep a precise and exhaustive record of ship positions – noting down steering positions or positions every hour when in open or coastal waters and ships’ position when transiting through landmarks when in confined waters. Other records, snapshots, and reports from third party service providers can be used as supporting evidence.

For more information, please contact your manager at the Club.