Lateral Marks and Preferred Channel

What lateral marks do and the direction of buoyage

In short: lateral marks are the edges of the road. They only make sense once you know which way the road runs.

Read first: IALA Buoyage System and Light Characters (regions, direction of buoyage, light abbreviations). This is the second topic of the Buoyage area.

• Lateral marks show the port and starboard sides of a well-defined channel or route (IALA R1001).
• Port and starboard are named as seen by a ship going with the direction of buoyage.
• Direction of buoyage: from seaward into a harbour, river or estuary. Elsewhere set by the authority, generally clockwise round land masses. Where in doubt, the chart shows it with a magenta arrow.
• Lateral marks can be buoys or fixed beacons. They may also mark a single obstruction outside the channel; keep to the side the mark tells you (33 CFR 62.25).
• They may carry numbers or letters that match the chart — a quick check of where you are in a long channel.
• On the bridge: outbound, you are going against the buoyage. In Region A the red marks are now on your starboard hand. Say it aloud in the pilotage briefing so the whole bridge team has the same picture.

Port and starboard marks in Region A and Region B

In short: shapes never change; colours swap between regions. Region A (Europe incl. Malta and the UK, Africa, Australia, most of Asia): red to port entering. Region B (the Americas, Japan, South Korea, the Philippines): red to starboard entering.

• Memory hooks: Region A — “Is there any red port left?” (red to port entering). Region B — “Red Right Returning”.
• Black for green: where an authority finds green unsuitable for a buoy, it may exceptionally use black instead (Canadian Chart 1, Section Q).
• On the bridge: a yacht crossing from the Med to the Caribbean or Florida changes region. Brief the bridge team before landfall: from now on, red marks are left to starboard when entering.

Why shape and topmark matter

• Colour is not always easy to read: low sun behind the buoy, dusk, haze, or a red-green colour-blind watchkeeper.
• The shape gives the side without the colour: can = port, cone = starboard, in both regions.
• A pillar or spar buoy has no telling shape. Then you rely on the colour, the topmark (can or cone) and, at night, the light colour.
• The system is built so a mark can still be identified if its light fails or its topmark is lost.

Lateral lights

In short: the light is the colour of the mark. The rhythm is free, except for one: Fl(2+1).

• Colour: red on a red mark, green on a green mark. So in Region A a red light is a port-hand mark entering; in Region B it is a starboard-hand mark.
• Rhythm: continuous or flashing — any rhythm except composite group flashing (2+1) (IALA R1001). Typical chart examples: Fl R 5s, Fl(2) G 6s, Q G.
• Fl(2+1) is kept for preferred channel marks, so you can tell a split in the channel at night.
• On the bridge at night: colour first, then count the flashes and time the period with a stopwatch. Compare with the chart only after that.

Preferred channel marks

In short: where a channel divides, a modified lateral mark tells you which branch is preferred. Read the main colour and shape as a normal lateral mark for the preferred channel; the broad band is for the secondary channel.

• The rule: the top (main) colour shows the preferred channel side. Taking the preferred channel, treat the mark as the lateral mark of its main colour. Taking the secondary channel, treat it as the mark of the band colour (33 CFR 62.25).
• Example — Region A, entering: red can with a green band ahead, Fl(2+1)R. Preferred channel is to starboard; leave the mark to port. If you want the secondary (left-hand) channel, leave it to starboard as if it were green.
• These marks may also mark a wreck or obstruction that can be passed on either side (33 CFR 62.25).
• Light: Fl(2+1) is the only rhythm they use and the only mark that uses it — the night-time signature of a split channel.

Common trap: reading the band as the main colour. A red buoy with a green band is still a red (port-hand, Region A) mark for the preferred channel. The band only matters if you choose the secondary channel.

Lateral marks on the paper chart and on ECDIS

In short: the MCA syllabus asks you to recognise IALA A and B marks and state their meaning on both a paper chart and an ECDIS. Same mark, different symbol.

Paper chart

• The buoy is drawn in its shape (can, cone, pillar, spar), with any topmark on top.
• Colour letters beside it: R = red, G = green; preferred channel RGR or GRG (read top to bottom).
• A lit buoy has a magenta light flare, with the character written next to it, e.g. “Fl.R.5s” or “Fl(2+1)G.10s”.
• Numbers or letters painted on the buoy are shown next to the symbol.
• The full list of symbols is in the chart key, INT 1 / Chart 1, Section Q (buoys and beacons).

ECDIS

• An ENC shows buoys with paper-chart (traditional) or simplified symbols. The operator chooses; the meaning does not change.
• To read the full light (colour, rhythm, period), pick the object with the cursor.
• Do not assume the region: check the colour on the ENC and the direction of buoyage.
• On the bridge: if what you see on the water does not match the chart or ECDIS (missing buoy, wrong light), slow down, fix the position by other means and check NP735 and the latest Notices to Mariners.