Maritime communications is the software and network that let a ship's crew send messages, call home and use apps at sea, and that carry data between the ship and the office on shore. Out at sea, there are no mobile towers. So almost all of this travels by satellite, through maritime and aviation satellite internet.
A large cargo ship has a crew of about 20 people, who spend four to nine months on board. For them, the link to home matters. Crew members want to message their families, make video calls and use banking apps. Ship managers know that a crew that can stay in touch is more likely to sign on again. So many ships offer crew internet, often with a fixed amount of data for each person each month.
The same link carries the ship's working data. The engine room sends its fuel use and machine readings to the office. The master, the captain of the ship, sends a noon report, a daily report of the ship's position, speed and fuel. The office sends back weather routes, updated documents and orders for supplies.
Satellite data has long been slow and costly, so this software is built to use it carefully. Consider a ship carrying new cars from Chennai to Durban, in South Africa, with a third engineer from Thrissur on board. He wants to send his family a video of 40 megabytes. The crew app does not send it at once. It compresses the video and keeps it in a queue until the night, when the ship's working traffic is low. Meanwhile, the ship's request for a spare pump reaches the office in a few seconds, because the software gives working messages priority. If the link drops in bad weather, the app keeps both in its queue and sends them when the link returns. The video is counted against the engineer's monthly data allowance.
Newer satellites in low earth orbit now offer much faster links, as the page on LEO and GEO satellites explains. With faster links, ships can send more data to shore and run more of their software from shore. That raises a risk. A ship's navigation and engine systems were once cut off from the internet. Now they are connected. So maritime cyber security keeps the crew's internet separate from the ship's control systems.
The office end of the link is usually ship management software, which receives the ship's requests and reports. Maritime communications is one of the ship's tools described under ocean freight and customs.