Why harbour waters speak their own language

Out on the open water, the rules are familiar: keep a good lookout, follow the Collision Regulations, give way as required. Cross the harbour entrance, though, and a second layer of information switches on. Signal masts, flag hoists, sound blasts from a ferry and a speed limit sign half hidden by a mooring buoy all carry meaning, and missing them is how an easy passage turns into an awkward conversation with the harbour master.

Harbour waters are working waters. Commercial craft, chain ferries, fishing boats and pilot launches have schedules to keep, and their manoeuvring options are often limited by draft, berth or tide. Every UK harbour operates under its own set of General Directions and byelaws made by the harbour authority, and those take precedence over general practice. The practical trick is simple: the local rules are almost always signposted, published and repeated on the harbour's own VHF channel. Your job is to expect them and read them.

Signal flags worth knowing

Flag signals are still flown from harbour flagstaffs, signal stations and sometimes from the vessels themselves. The International Code of Signals gives you a working vocabulary, and a handful of flags cover most of what you will see around the coast.

• Flag A (Alpha) – white and blue swallowtail, meaning "I have a diver down, keep well clear and slow down". Treat it as a hard instruction, not a suggestion.
• Flag B (Bravo) – red swallowtail, carried by vessels loading, discharging or carrying dangerous goods.
• Flag Q (Quebec) – plain yellow, flown by a vessel requiring pratique; you will see it on arriving ships before they come alongside.
• Flags N and C together – the classic international distress signal, and worth teaching to everyone aboard.
• Flag O (Oscar) – man overboard. Flag V (Victor) asks for assistance; Flag W (Whiskey) requests medical help.
• Flags C and N separately – the old yes/no pair, still used to answer harbour signal station questions without radio.

Many harbour authorities also fly their own house flags or pennants to indicate berthing instructions, lock status or a tide gate being open. If you do not recognise one, call the harbour office or the signal station on VHF rather than guessing.

Light and shape signals at the entrance

Traffic signals at harbour entrances, locks and swing bridges are the ones people misread most often. The convention is broadly consistent around the UK: a fixed green means you may proceed, fixed red means stop and wait, and amber or yellow usually means proceed with caution or stand by for a change. Where three lights are shown vertically, the combination matters – three reds typically means the harbour or lock is closed, and a green over a red or similar pairing can indicate a limited or one-way movement.

Do not creep past a red simply because the water looks clear. It may be held for a ferry, a departing ship or a lock emptying. Day shapes matter too, and so do the signage boards mounted on piers and breakwaters, which often carry the speed limit, the VHF channel and the direction of the fairway in a single panel.

Sound signals – listening as a skill

Away from the buzz of an engine, a sound signal tells you someone's intention before you can see it. The basics, drawn from the Collision Regulations, are worth knowing by heart.

• One short blast – I am altering course to starboard.
• Two short blasts – I am altering course to port.
• Three short blasts – I am operating astern propulsion.
• Five or more short, rapid blasts – I am unsure of your intentions, or I doubt you are taking enough action. Answer it, and answer it clearly.
• One prolonged blast – leaving a berth, or approaching a blind bend in a narrow channel.
• Two prolonged blasts – a vessel about to leave a dock or berth on a commercial scale.

Ferries, tugs and pilot boats use these constantly in confined water, so keep a hand near the horn and reply to any signal directed at you. In fog or at night, the same signals still apply, and a listening watch becomes as important as looking.

Speed limits, wash and no-wake zones

Most UK harbours set a blanket speed limit, commonly four, five or six knots, and it usually applies from the harbour limit line rather than from the first pontoon. The number on the sign is not the real point, though. The real point is wash. Your speed should be the fastest that produces no breaking wash along the banks, no slapping of moored hulls and no risk to anyone on a paddleboard or in a small dinghy.

A few practical notes. Speed over ground shown on a GPS is not the same as speed through the water, and a strong tidal stream can have you exceeding the limit while your log reads politely. In areas with moorings, pontoons, rowing clubs or nature reserves, assume a stricter limit applies even when nothing is posted. Where a harbour sets a no-wake zone, it means exactly that, and it is often patrolled.

Local rules that catch people out

Every harbour has its own quirks, and the ones that catch visiting sailors tend to be the same few categories.

• VHF channels. Harbour control usually works on a specific channel, often 11, 12 or 14, with 16 for calling. Monitor it and keep transmissions brief.
• Priority traffic. Chain ferries, commercial vessels and, in some ports, vessels under pilotage have priority in the fairway. Keep the channel clear and pass on the side indicated.
• Anchoring bans. Submarine cables, dredged channels, mooring areas and protected seagrass beds are all no-anchor zones, and the chart may not tell you.
• Discharge rules. Many harbours and marinas prohibit any overboard discharge, including grey water, and berth holders are expected to use pump-out facilities.
• Berthing and locking. Get permission before you tie up, and never enter a lock or a marina berth until you are told to.

Before you cast off, spend ten minutes on the harbour authority's own sailing directions, note the speed limit, the VHF channel and the sound signals you are likely to hear, and brief your crew on what you have found. The reward is a passage that feels calm, unhurried and welcome – the way harbour waters are meant to feel.