Coastal navigation


The first requests for sea level information arose from the needs of inshore navigation and access to ports with substantial tidal ranges. There was a need for real-time or only slightly time-delayed measurements. 


Entrée de la Penfeld, Port militaire de Brest (Crédits SHOM - Nicolas Pouvreau, juillet 2012)



To meet this need, the information was obtained by direct vision:

  • Either from the tide staff available at the entrance to ports or along channels in the maritime portion of rivers;
  • Or, in the major seaports, daytime signals using cones and cylinders, and night-time signals using green, red and white lights.


Détail des échelles de marée positionnées à l'entrée de la Penfeld, Port militaire de Brest (Crédits SHOM - Nicolas Pouvreau, juillet 2012)



More modern systems were developed in some estuaries where water depths measured at different tide stations were transmitted by radio to ships, in particular VHF voice radio (Port of Nantes - Saint-Nazaire, Port of Bordeaux , Port of Rouen).


Observatoire marégraphique de Nantes Salorges (Crédits SHOM - Nicolas Pouvreau, 21 juin 2012)



The uncertainty in the water level has repercussions on the navigation margins, which are the safety margins between the seabed and the vessel. In addition, due to the costs of operating large ships (waiting on roadstead is very expensive) and the need to maximise returns on port facilities, the Marine Services and pilots are increasingly demanding when it comes to the quality of tide measurements. Currently the precision required is on the order of five centimetres (± 5 cm).


Bateau naviguant dans le pertuis d'Antioche avec en premier plan un marégraphe optiwave déployé sur l'île d'Aix. Crédits SHOM - Nicolas Pouvreau, mars 2011 Cliquez sur l'image pour l'agrandir


To find out more



  • La Marée - La marée océanique et côtière - Bernard Simon. Editeur Institut océanographique, 2007, 434pp.


Last updated: 12/12/2012