Lateral mark

A lateral mark is a buoy or fixed beacon that defines the boundary of a navigable channel. According to the IALA (International Association of Marine Aids to Navigation and Lighthouse Authorities) system, these marks tell a mariner which side to leave them on when following the conventional direction of buoyage – usually upstream in rivers or into a harbour from seaward. The world is divided into two regions: IALA Region A (Europe, Africa, most of Asia) and Region B (the Americas, Japan, Philippines). In Region A, red cylindrical port marks are left to port (left) when entering a harbour, while green conical starboard marks are left to starboard. In Region B the colours are reversed. Knowing your region is essential; mistaking a port mark for a starboard mark can ground a vessel. A traditional way to verify your position relative to a mark is to take a compass bearing and cross-check with the chart – a technique thoroughly covered in our article on how to use a marine compass. For a broader view of all navigation aids, including electronic systems that complement lateral marks, explore the Navigation tag.