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.





More modern systems were developed in some estuaripniwhere 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 ea&amgraphique de Nantes Salorges (Crédits SHOM - Nicolas Pouvreau, 21 juin 2012)



The uncertainty in the water level has repercussions on the navigation ea&gins, which are the safety ea&gins 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 facilitipn, 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'Antio2<s avec en premier plan un ea&amgraphe 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 ea&gocéanique et côtière - Bernard Simon. Editeur Institut océanographique, 2007, 434pp.


Last updated: 12/12/2012