Overlay film (radar)

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Overlay film (greatly simplified image)
Radar screen on a ship
Typical shipping traffic in straits
Example of a digital nautical chart

Overlay foils (also called overlays for short ) are usually transparent plastic foils that can be filed in folders to support the radar navigation of watercraft .

use

Overlay films are a commonly used tool in the maritime order in narrow fairways with radar-based navigation propelled by solid distinguish radar echoes. Moving radar echoes are z. B. accompanying, crossing or oncoming watercraft , while fixed radar echoes are fixed or floating sea ​​marks . Since navigation marks are often equipped with radar reflectors for better recognition , the size of the radar echo does not give a reliable indication of the object. On the radar screen (often also called screen ), both moving and fixed radar echoes move relative to the ship's own movement. However, the moving echoes are far more important for the ship's command, as they distinguish the “dangerous” watercraft from the more “harmless” navigation marks.

In order to be able to distinguish the two radar echo forms from one another, transparent plastic foils are used on which the nautical symbols are painted from the corresponding nautical charts , to the scale of the radar screen. These foils are placed on the radar screen when passing through the strait or at the entrance to the port , aligned with the nautical signs that can then be identified and carried along by hand on the radar image. The radar echoes from watercraft can now be seen more clearly and better observed by the ship's command.

The use of overlay foils can significantly reduce the number of collisions or other accidents .

  • Adaptation of the overlay film to the radar screen and the navigation mark echoes

  • The three “fellow travelers” can be better observed by recognizing the sea mark

  • Manual shifting of the overlay foil along the navigation mark echoes

The above-described overlay foils are produced by experienced navigators on board the ships themselves. Due to frequent changes of buoys on the sea routes, they have to be constantly updated. The basis for this is the weekly news for seafarers (NfS), according to which the analogue nautical charts must also be updated.

Radar overlay

Modern radar overlay works electronically in that radar and digital nautical chart images are displayed synchronized on a monitor and the updates are also imported automatically.

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