A fanbeam is used to measure distance accurately, and is often used with dynamic positioning.

In short its a fully automated and highly reliable laser rangefinder.

A fanbeam system is built up from the following components:

The laser is the item that gives the name "fanbeam", as the laser spreads out like a fan when looking for the reflector (instead of the "single beam of light" that most lasers use).

One mounts the laser and computer onboard the vessel, while the reflector is mounted on a fixed installation. Most often this is oil platforms, but this can also be other ships - in case one needs to dock with them, or just need to hold a distance. The laser will now target the surrounding area, and when it locates the reflector, it will report back to the computer. The computer can then measure the time it takes for the light to travel to the reflector and back, and calculate distance to the reflector based on the speed of light. The actual position is then reported to the ship, and it can then base it's course settings on this data.

Current (cost effective) state of the art device has a range of 2000 km, and an accuracy of 10 cm. The fanbeam system is often combined with GPS or other reference systems.

It is not recommended to mount the system so that the laser will have to look into the sun to get a reading. The added radiation will confuse the hell out of the computer, and the planned, careful operation can turn out to be a mad dash for the manual overrides.