Sailing and trading at the deep blue ocean needs brave heart, calmness, sincerity and technology. There are many hazards that a sailor needs to consider while riding through the waters. Communication and navigation are the most vital of them. It is pivotal for a sailor and commercial voyage to remain contacted with the water authorities for safety concerns. Sailing becomes far safer with the invention of latest technologies and devices. In this write up, we are going to explore an important device that’s helpful to connect a voyage with the other ships sailing at the same ocean. The device is called Automatic identification system. Let’s learn this innovative way of navigation and communication for sailors in brief.
Each time slot represents 26.6 milliseconds VHF radiowave time slots The AIS of ship A sends the position message in one time slot. At the same time it reserves another time slot for the next position message The same procedure is repeated by all other AIS-equipped ships AIS Receiver 3. AIS signals are identified by MMSI number. A number of time slots. When a Class A or B switches on, it looks for a vacant time slot and reserves it. Other sets in range will avoid this slot and select another one. Precise timing is needed to ensure that all vessels are synchronised and this is derived from GPS; hence why Class A/B equipment has its own GPS receiver.
This timing is determined by the reference time UTC (obtained in the MAC), common to all AIS receiving stations integrated into a region of coverage. Within the AIS standard, each slot has a duration of 26.67ms. If each frame has a time duration of AIS of 60s, the total number of slots in a frame AIS is N ¼ 60 Δt slot ¼ 60 slots (1).
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Introduction [What is AIS?]
Automatic identification system, shortly called AIS is an automatic tracking system used by ships for identifying and locating other nearby vessels. This device helps you to exchange information like unique identification, speed, location, position and course of other nearby ships on the screen or ECDIS. It is designed with an intention to assist a ship’s watchstanding officer by allowing him to track and monitor other vessel’s movements. AIS can be integrated with standardized VHF transceiver with a positioning system like GPS receiver. It is compatible with electronic navigation sensors like gyrocompass. AIS base stations are located along with the coastline to track the vessels with their transceivers. When the vessel is out of coverage, AIS base satellites are used to track and monitor the vessel.
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Types of AIS
AIS of Class A
The class A is designed for large vessels travelling for international voyages. They are providing increased range and 100% accurate data which make the journey safe for the large commercial vessels. It also uses self-organized time division multiple access to transmit their data.
AIS of Class B
Class B transceivers were pioneered to offer AIS benefits to smaller vessels. Class B devices offer lower power, fewer receivers and different display options to a Class A transceivers. It is quite affordable for small and medium scale boat owners.
AIS ATON (Aid to Navigation)
It is specially designed for Aids to Navigation by including chaining which enhances the AIS base station’s range, weather and sea monitoring capacities. It makes vessel monitoring and tracking completely easy for the rescue team.
AIS SART (search and rescue transmitter)
It offers enhanced location finding data in emergency circumstances. Sending the life raft's position, heading and speed have become a completely ease with the AIS data. This is the primary benefit over other technology as it allows rescue craft to plan an intersect course quickly and efficiently.
AIS base station
AIS base stations offer the chance to form an AIS network long a country's coastline that enhances national security and forms a link between the sea and monitoring center further inland. AIS base stations are able to relay information from ATONs as well as vessel information to a monitoring or command center further inland, aiding national security.
How it works?
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AIS needs a VHF transmitter, a receiver and a common electronic communication device like a radio. It uses 9.6 kb GMSK FM modulation over 25 or 12.5 kHz channels using HDLC packet protocols. It uses time division multiple access i.e. TDMA to share VHF frequency (VDL). There are two dedicated frequencies called AIS 1 and AIS 2. The VDL is divided into 2250 time slots which are arranged into frames, which are repeated at every one minute. Each AIS unit sends a report to one of the time slots at the same time. AIS units that are in range to each other listen, record, read all the time slots and display the information into the radar screen.
AIS for class A and class B are using same TDMA, but their information is different. All types and classes of AIS use a Maritime Mobile Service Identity i.e. MMSI to transmit on the VHF frequency. Those vessels that are using digital selective calling means radio have the same MMSI number as the frequency of the radio. The 6 digits MMIS number of each vessel is unique and can be tracked differently.
Uses of AIS
Since its inception, AIS is contributing a vital link of navigation for the nautical industry. It’s nearly impossible to commence the following important tasks for maritime industry.
- To manage heavy traffic at different nautical channels.
- To avoid any unforeseen circumstances like shrinking of ship, accident and many others.
- To successfully implement rescue operations in unforeseen circumstances.
- To find best direction for navigation during rallies and other situations.
- It is used for exchanging information between the vessels.
Requirement of AIS
Is your vessel required to have AIS? This is the vital aspect for your voyage to commence trade on the waters. Here, we are describing some of the vital regulations of International Maritime Organization that obligate fleet to be fitted with approved AIS. These AIS carriage requirements are only liable to commercial vessels that are subjected to Safety of Life at Sea.
- International voyage with 300 or above gross tonnage
- Local cargo ships with 500 or above gross tonnage
- All passenger ships irrespective of size.
No matter you are having a private yacht or a commercial voyage, it is essential to take the benefits of latest nautical technologies to prevent any hazard or accident.
Does your fleet use automatic identification system? If your answer is yes, then let’s discuss some of the advantages into the comment box below.
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