IALA A lateral marks

Signposts at sea

Module 2 gave you ways to fix your position: compass bearings, transits and dead reckoning. Close to land, though, much of the navigating is done by eye, and what you look for most are the buoys and beacons that mark the way in and the dangers along it. Module 3 starts with them.

A buoy is a floating mark, moored to the seabed, so it swings a little with the wind and tide. A beacon is a fixed mark: a pole, post or tower standing on a rock or the seabed. Both are marks (aids to navigation). They use the same colours and shapes, many carry a topmark — a small shape on top — and many are lit.

Almost every seafaring country lays its marks to one scheme: the IALA Maritime Buoyage System, set up by IALA, the international body for marine aids to navigation. It has lateral marks (this lesson), cardinal marks (Lesson 17), and isolated danger, safe water and special marks and the emergency wreck marking buoy (Lesson 18). The world is split into two regions, which differ only in the colours of the lateral marks:

In Region A, going into harbour, red marks are on your port side and green marks on your starboard side.

This course and its practice chart use Region A, as do the UK, Ireland and the rest of Europe. If you sail further afield, find out which region you are in before you need to know.

The direction of buoyage

Lateral marks (from the Latin for “side”) show the sides of a channel: port-hand marks on one side, starboard-hand marks on the other. But your port side becomes your starboard side the moment you turn round, so the marks need an agreed direction to refer to. That is the conventional direction of buoyage:

• Approaching a harbour, river, estuary or other waterway, it is the direction you take coming in from seaward.
• Elsewhere — along a coast, say — it is set by the buoyage authorities, generally running clockwise around the continents. Charts show it with a magenta arrow wherever it might not be obvious.

Every rule about lateral marks is stated for a boat going with the direction of buoyage. Going against it — leaving harbour — everything reverses.

On the practice chart the direction is obvious, so no arrow is printed: it runs from seaward into Port Kerran, north up the buoyed channel.

Port-hand and starboard-hand marks

A can buoy is an upright cylinder with a flat top; a conical buoy comes to a point. Larger marks are often pillar buoys (a tall structure on a broad base) or spars (a pole floating upright). Their shape says nothing about the side, so the colour and the topmark do the work. Lights on lateral marks are red or green to match the mark, and may have any rhythm except Fl(2+1), which is kept for the preferred channel marks you will meet below.

Going with the direction of buoyage: red cans to port, green cones to starboard.

Into Port Kerran

The approach to Port Kerran is a short buoyed channel running north into Kerran Bay. Kerran Approach buoy, a red and white safe water mark (Lesson 18) with navigable water all round it, marks the start. 1.6 M north of it is the first pair of lateral marks: No 1, a green cone, on the east side, and No 2, a red can, on the west, 5.4 cables apart. Another 6.5 cables on, at the inner end, are No 3 and No 4, 4.9 cables apart.

Coming in from seaward you are going with the direction of buoyage, heading north: the green cones pass down your starboard side and the red cans down your port side. The leading lights you used in Lesson 13, in line on 000°T, take you straight up the middle.

Notice the numbers. Here, as on many charts, the starboard-hand marks have odd numbers and the port-hand marks even ones, counting up from seaward — in the direction of buoyage. It is common practice rather than a rule you can rely on everywhere, so always read the numbers from the chart.

Lights: telling them apart at night

At night you see neither the colour of a buoy nor its shape — only its light. Lateral marks are lit in their own colour, so the colour alone tells you the side: red, port-hand; green, starboard-hand. To tell one buoy from its neighbour you need the rhythm, printed beside every lit buoy on the chart. Lesson 19 decodes light characteristics in full; for now you need three parts:

• Fl — flashing: short flashes with longer darkness between. Fl(2) means the flashes come in groups of two; Fl(3), groups of three.
• R, G — the colour, red or green. A light with no colour letter is white.
• 5s — the period: the time the whole pattern takes to repeat, from the start of one flash (or group) to the start of the next.

Leaving harbour: everything reverses

Leaving harbour you are going against the direction of buoyage, so the sides swap: the red port-hand marks pass down your starboard side and the green starboard-hand marks down your port side. The marks haven’t changed — you have turned round.

Preferred channel marks

Sometimes a channel divides. Where it does, a modified lateral mark — a preferred channel mark — can show which branch is the preferred, or main, channel. It is a port- or starboard-hand mark with one broad horizontal band of the other colour:

Read the main colour first. A mostly red can is a port-hand mark: keep it to port and you are in the preferred channel, which lies to starboard of it. You can still take the other branch if it suits your boat better — you then keep the mark on your other side. At night the light matches the main colour and flashes in groups of two, then one: Fl(2+1), a rhythm lateral marks use only for preferred channels. There are no preferred channel marks on the practice chart.

When colours let you down

Colours aren’t always visible. Looking into a low sun every buoy is a black outline; at dusk, in haze or at a distance, red and green are hard to tell apart; paint fades and weed grows. That is why lateral marks differ in shape as well as colour: can for port, cone for starboard, with topmarks to match. On pillars and spars, where the body’s shape doesn’t help, the topmark does.

Find the direction of buoyage first. Going with it: red to port, green to starboard. Going against it: the other way round.

Next: cardinal marks, which tell you where the safe water lies around a danger using compass directions instead of port and starboard.