Why Poor Visibility Deserves a Proper Plan

Fog and heavy rain rarely arrive with a polite warning. On a busy stretch of coast — the Solent, the Thames approaches, the Bristol Channel, the Firth of Clyde — visibility can drop from five miles to a few hundred metres in under half an hour. By then you may already be committed to an approach, with shipping lanes on one side, a harbour entrance ahead and a rising tide behind you.

The answer is not heroic seamanship in the murk. It is preparation done in clear weather, at the chart table, with a cup of tea and plenty of time. Waypoints entered properly, radio calls rehearsed and alternative anchorages identified before you need them turn a stressful approach into a manageable one.

Build a Waypoint Plan You Actually Trust

Start with the entrance itself. Identify a safe water waypoint at least half a mile off the harbour mouth, clear of any overfalls, pot buoys and the inevitable cross-channel ferries. Then build a short sequence of waypoints leading in — outer approach, mid-channel, inner harbour — each one checked against the chart for depth and lateral marks.

Two habits make a real difference:

• Use named, meaningful waypoints rather than numbers. "Needles Fairway" or "Porthleven Outer" will be far easier to pick out on a small chartplotter screen when you are cold and peering through drizzle.
• Keep the route simple. A handful of legs is easier to monitor than a dozen. Fewer waypoints mean fewer chances to mis-identify one in poor light.
• Note the clearing bearings for each leg — the heading that keeps you safely off a headland, a shoal bank or a harbour wall. Write them on a laminated card in the cockpit.
• Check your GPS accuracy assumptions. A consumer receiver is usually excellent, but a chart datum offset or a poorly surveyed harbour plan can put you closer to the putty than the screen suggests.

If your plotter fails, you should still be able to run the approach on paper. Mark the same waypoints on the chart, and note the times and distances between them at your expected speed. That is your fallback, and it is worth practising once in daylight.

Sort the Radio Before the Fog Arrives

Poor visibility makes VHF discipline essential. Know which channels the harbour, port control and local marinas use, and have them written down where the helm can see them. In the Solent that means Southampton VTS and QHM Portsmouth; on the east coast, Harwich and Dover Coastguard; in the west, Milford Haven and the Bristol Channel ports.

When you call, be brief and useful. Give your position, course, speed, destination and intentions. A short, clear message is far more valuable to a ferry master than a rambling one.

• Make the call early. Ten minutes before the entrance, not once you are in the middle of a traffic lane.
• Listen first. Know what other vessels are doing before you transmit.
• Use the right channel. Channel 16 for calling, then move to a working channel as directed.
• Log your calls and positions. A simple notebook entry with time, position and who you spoke to is invaluable if anything goes wrong.

If you carry AIS, use it to watch for converging traffic, but never rely on it alone. Small fishing boats, yachts without transponders and unlit pot markers will not appear on the screen.

Choose Alternative Anchorages in Advance

Fog often makes an entrance unwise rather than impossible. Having two or three bolt-holes marked, with their approach notes and depths already recorded, gives you the confidence to turn away rather than press on. Think about shelter from the prevailing wind, tidal range, holding and whether the anchorage is clear of a busy channel.

Useful attributes for a fog anchorage include:

• Wide, deep water with plenty of swinging room and a soft mud or sand bottom.
• A straightforward approach that does not depend on spotting a small buoy at close range.
• Good VHF coverage and, ideally, a harbour authority that knows you are there.
• Shelter from wash and swell, since you may be waiting several hours.

Write down the latitude and longitude of each alternative, plus a rough note of the safe approach. If fog catches you off a strange coast, you will be very glad of a plan made in sunshine.

Practise the Radar and Sound Signal Routine

If you have radar, spend an hour in clear weather learning to tune it, set the gain and interpret the picture. In fog, reduce clutter, use a longer range to see approaching traffic early and keep the display on a steady, familiar setting. Do not chase perfect definition; take the information you can get and combine it with what you see and hear.

Sound signals still matter. A power-driven vessel making way sounds one prolonged blast every two minutes; a sailing vessel sounds one prolonged plus two short. Listen for others doing the same, and do not assume silence means empty water — small craft often stay quiet.

Post a lookout forward if you can, brief everyone on what to watch and listen for, and slow down. Speed is the enemy of reaction time in fog, and a gentle approach gives you room to stop, turn or anchor short of trouble.

A Short Checklist for the Chart Table

Before any coastal passage, take ten minutes to run through this list. It is quick, it is cheap and it turns a potentially frightening approach into a routine one.

• Waypoints: named, checked, with clearing bearings written down.
• Charts: paper backup ready with the same route marked.
• Radio: harbour and coastguard channels noted, call script drafted.
• Anchorages: two or three alternatives with positions and approach notes.
• Radar and sound signals: settings known, routine briefed to the crew.
• Crew briefing: everyone knows the plan, the fallback and their job.

The coast is just as rewarding in mist and rain as in sunshine — provided you have done the thinking beforehand. Plan the approach, plan the call, plan the retreat, and you can enjoy the quiet grey hours afloat rather than dread them.