Improved AIS: This is how the tracker for the Sea-Eye and the Seefuchs works 

 

Example of how the AIS works on an oil platform

By Frank Scholz

For the past six weeks, a new piece of equipment for improved ‘visibility’ on the Internet has been tested on the rescue ships Sea-Eye and Seefuchs.

The past often saw periods of several hours to entire days, during which the positions of the rescue ships were not updated on the Internet. This had technical and physics-related reasons.

The presentation of the ships’ positions is based on the ‘Automatic Identification System’ or AIS. Around the globe this system is obligatory for commercial vessels. Many yacht owners have also opted to buy the equipment.

Similar to plane transponders, the ships’ position, course, speed and other data are sent permanently via UKW-radio waves.

The relevant receivers on the ships feed the data into the navigation computers, which produce an updated situation report of the ship’s movements and present it clearly on the screens on the bridge.

Additionally, based on the data, the computers calculate the danger of collisions and alert the bridge crew on time.

Port authorities and traffic coordination centres ashore also use the system, in order to guide ships through narrow shipping channels.

For several years, the ships’ movements have been freely accessible on the Internet. This is possible thanks to land stations, which also receive the signals and transmit them to the servers of companies like Marinetraffic, Vesselfinder etc. On their websites anyone can search for specific ships and follow their positions.

These land stations or AIS-Dispatcher Stations are usually operated by authorities or amateur radio enthusiasts. They span the earth’s coasts like a close-knit net. This is necessary because the reach of the radio waves is only 20-60 kms; in case of occasionally happening favourable weather conditions also up to 300 kms.

This used to be a problem for the visibility of rescue ships off the Libyan coast because no land stations exist there that further transmit the signals. The closest stations are in Sicily and in Sousse, Tunisia. Too far away for a reliable and complete reception and transmission to the Internet.

This problem has now been solved as the ships themselves transmit their AIS data via satellite to the Internet. They function as swimming ‘land stations.

In order to achieve this, our volunteer engineers had to develop a filtering system to reduce the data volume, because the unfiltered transmission to satellites would accumulate transmission fees of several thousand Euros per month. Each megabyte costs between 10 and 20 Euros.

Only AIS signals from ships within a radius of four nautical miles around the rescue ship are considered and the transmission frequency per ship is reduced to a maximum of one transmission every five minutes. These two elements reduce the data volume in the not very frequented waters off the Libyan coast by about 99%.

After the successful test of the first installation on the Seefuchs, its twin ship Sea-Eye was also equipped with one. Competent crew members solved the initial problems with the connection to the satellite radio system, so now this ship is also reliably able to make its position known to the public.

We are hoping for more safety in case of possible conflicts with the so-called Libyan coast guard and for fewer conspiracy theories from Italian authorities about allegedly switched off transponders (even our Interior Minister fell for that).

For financial reasons, the Seefuchs and the Sea-Eye only transmit the AIS data to the service Marinetraffic, to which we have established a link on our homepage.