World Library  
Flag as Inappropriate
Email this Article

Sea mark

Article Id: WHEBN0000489788
Reproduction Date:

Title: Sea mark  
Author: World Heritage Encyclopedia
Language: English
Subject: Cairn, Isolated danger mark, Lateral mark, Special mark, Daymark
Collection: Buoyage, Coastal Construction, Coastal Fortifications, Nautical Terms
Publisher: World Heritage Encyclopedia

Sea mark

The Ketch Popoff, approaching Concarneau harbour and passing between the sea mark buoys of the entrance, while an approaching trawler in the background sails around the red buoy

A sea mark, also seamark and navigation mark, is a form of aid to navigation and pilotage aid which identifies the approximate position of a maritime channel, hazard and administrative area to allow boats, ships and seaplanes to navigate safely.

There are three types of sea mark:

  • beacons - fixed to the seabed
  • buoys - consisting of a floating object that is usually anchored to a specific location on the bottom of the sea or to a submerged object
  • A type of cairn built on a submerged rock/object, especially in calmer waters.

Sea marks are used to indicate channels, dangerous rocks or shoals, mooring positions, areas of speed limits, traffic separation schemes, submerged shipwrecks, and for a variety of other navigational purposes. Some are only intended to be visible in daylight (daymarks), others have some combination of lights, reflectors, bells, horns, whistles and radar reflectors to make them usable at night and in conditions of reduced visibility.

Marks are shown on nautical charts, using symbols that indicate their colour, shape and light characteristic, and are usually identified by name or number.

The International Association of Lighthouse Authorities defines one system of marks specifying the shapes, colours and characteristic lights of buoys depending on their purpose, the IALA Maritime Buoyage System. For historical reasons, there are two regions of lateral marks in use:

The two regions differ principally in the colours used to denote the two sides of a channel. When approaching a harbour from seaward, Region A places conical green marks to starboard and cylindrical red ones to port. In Region B these are replaced with conical red marks to starboard and cylindrical green ones to port. This can be remembered (for Region B) with the mnemonic "Red, right, return". Another Region B mnemonic, which also helps with buoy numbering is "Even Red Left Port" (as in Eric the Red) - Even Numbered buoys are red, on your left (port) side leaving port. In any case, since in many harbours it is not always apparent which direction is seaward, buoys should be used in connection with the appropriate nautical chart. Additionally, since marks may be off station due to collision with ships, storms or other factors, they should be used with caution and not relied on solely for navigation. The two regions are often referred to as two systems, which was the original intent. In 1980 it was decided however to combine these systems and distinguish between regions.[1][2]

In a wider sense the phrase "sea mark" is often understood to include all kinds of landmarks, structures and devices that can be used to provide warning and guiding signs to mariners. Thus a sea mark can be and often is located on dry land. Examples of land-based sea marks are various signal lights and leading marks. The latter are mainly used to indicate the centerline of a fairway in narrow passages. Sea marks may also on occasion be used to help mark the boundaries of defensive sea minefields, or the safe lanes through same, especially during wartime.


  • See also 1
    • Mark types 1.1
    • Other 1.2
  • References 2

See also

Mark types



  1. ^ "IALA Maritime Buoyage System". IALA. Cardinal, isolated, safewater, special marks, new dangers, regions A and B 
  2. ^ "IALA Maritime Buoyage System". Nautical Issues. 
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from World eBook Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.