What to do when AIS fails in a busy shipping lane
When AIS dies before a shipping-lane crossing, the fix is not panic, but a 10-minute seamanship drill built on bearings, lookout, radar, and early aborts.
When the screen goes dark
AIS failure at the wrong moment is not a software hiccup, it is a seamanship test. In Yachting Monthly’s Channel scenario, Mike and Linda are more than halfway from Poole to St Peter Port in their Bavaria 38, *Isabel-J*, under an easterly Force 5 with a preventer rigged, the genoa poled out, and about six knots on the log. Ahead, the next line of ships sits like a wall. That is exactly when the skipper has to stop treating AIS as the decision-maker and go back to first principles.
The important rule is simple: AIS is useful, but it is not the collision-avoidance rulebook. The International Maritime Organization’s guidance says AIS has inherent limitations and should not be used solely to avoid collisions. UK Marine Guidance Note 324 goes further, warning that AIS may not give a complete or correct picture of nearby traffic and that collision-avoidance decisions should be based primarily on visual and or radar information. In plain cruising terms, the screen can support your judgment, but it cannot replace it.
The first 10 minutes after AIS failure
Treat the next 10 minutes as a reset, not a debate.
1. Hold the boat steady and keep the current sail plan.
Do not start experimenting with a big tack, a sudden gybe, or a dramatic heave-to unless you genuinely need to. The guidance in this seamanship case points toward keeping the sail plan as much as possible while making early, measured changes in course or speed. The goal is to stay predictable while you rebuild your picture of the traffic.
2. Post a proper visual lookout immediately.
AIS has gone, so your eyes become the primary sensor. One crew member should be dedicated to scanning the horizon, with particular attention to any vessel whose bearing appears steady while range is closing. That steady-bearing, reducing-range test is still the classic collision warning, and it is the one that matters when the electronics fail.
3. Take bearing notes, not guesses.
If you have a hand-bearing compass, use it. A quick series of bearings on the most worrying ships tells you far more than a vague impression of “they look close.” If the bearing is not changing, the risk is real, even if the target appears small or distant.
4. Use radar if it is fitted and working.
UK guidance is clear that collision-avoidance decisions should be based primarily on visual and or radar information. Radar gives you range, relative motion, and a second picture when AIS goes blank. If the plot starts to show a crossing situation developing, that is the moment to alter early, not when you are already in the close-quarters zone.
5. Keep VHF as a backup, not a crutch.
Calling a ship can be justified on occasion, but it is not a substitute for proper watchkeeping. UK guidance warns that misunderstandings can arise even where the language itself is not the problem. Use VHF only to clarify an already sound plan, not to negotiate your way out of a weak one.
6. Make an early, visible alteration if needed.
The best move is usually small and obvious: a clean course change or speed reduction that is easy for the other vessel to detect. Late, twitchy corrections are what create uncertainty. In busy water, clarity beats cleverness.
7. Set an abort point and respect it.
If the picture is not becoming simpler, stop trying to force the crossing. Heave-to, slow down, or hold position only if that creates a better opening and keeps you clear. If the lane is still packed and your bearing picture is not clean, wait for the gap rather than gambling on timing.
Why the Channel makes this harder
This is not open-water theory. The crossing in the column sits inside one of the world’s most managed shipping corridors, and the International Maritime Organization notes that Rule 10 of the 1972 COLREGs was a major innovation because it addressed traffic separation schemes. The first such scheme was established in the Dover Strait in 1967, which is a reminder that the Channel has been organized around ship flow for decades for a reason.
That matters on the Poole to St Peter Port run because the route threads past the Alderney Race, a strait between Alderney and Cap de la Hague with some of the strongest tidal streams in Europe. Admiralty guidance says the race is not recommended for ships other than those heading to Channel Islands or certain French ports. For a cruising yacht, that combination of heavy commercial traffic and hard-running tide turns a routine crossing into a very compressed decision space.
That is why Mike’s instinct to heave-to and wait is not foolish, and why Linda’s confidence in being under sail and clear of the TSS is only part of the picture. Being outside the traffic separation scheme does not remove the need to judge risk of collision by sight, bearing, range, and timing. If the ships are still on a converging picture, the rules and the seamanship point in the same direction: act early, or wait outside the danger.
Crew jobs that actually work
A good backup drill assigns roles before the lane comes alive. One person drives, one person scans, and if there is a third aboard, that crew member handles the compass, the radar plot, or the VHF set without cluttering the helm. That keeps the skipper focused on the one thing that matters: whether the crossing still looks safe enough to continue.
This is also where digital-era sailors can get caught out. If you have learned to sail with moving maps and target symbols, it is easy to overtrust the display and undertrain the eye. The column’s real warning is not about a broken transceiver. It is about how quickly confidence in electronics can erode traditional seamanship if you have never had to do the job without screens.
Rachael Sprot’s authority in this column comes from experience as a Yachtmaster Examiner with extensive sea miles, and the advice reflects that practical bias. The message is not to panic when AIS stops talking. It is to revert immediately to the oldest tools that still work: lookout, bearings, radar if you have it, careful VHF use, and the discipline to delay a bad crossing.
When the screen dies in a shipping lane, the safest response is rarely a heroic last-second maneuver. It is the calm, deliberate 10-minute drill that turns a silent box into a manageable passage again.
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