The Watch That Never Sleeps: How Sailors Are Rethinking AIS for Atlantic Crossings
by Erin Carey 22 Oct 22:38 BST
14 November 2025
Every November, a large flotilla of yachts gathers in the Canary Islands before pointing their bows west. Over the following weeks, the Atlantic Rally for Cruisers and the hundreds of boats crossing independently alongside it will spend two to three weeks at sea, often with crews of just two or three people standing round the clock watches across thousands of miles of open ocean.
It’s one of sailing’s great rites of passage and also one of its quietest hazards. Out there, traffic is sparse. But that sparsity is precisely what makes it dangerous. After days of empty horizon, it's easy for even an experienced watchkeeper to lose focus, and a 300-metre container ship doing 20 knots can close the distance from “barely visible” to “collision course” faster than most people expect.
For decades, the tool standing between a crew and that risk has been the same: a hardwired AIS receiver, a VHF antenna, and a reasonably alert set of eyes. It has worked, for the most part. But “for the most part” becomes a less comforting phrase the longer you look at the numbers.
What’s the Issue?
Shipping lanes have a way of turning a quiet passage into a puzzle with almost no warning. A handful of AIS targets can appear within minutes of each other, each on a different heading, each closing at different speeds, and working out which one actually matters becomes a genuinely tense exercise. At night, when there's no horizon to judge distance by eye and every light on the water looks roughly the same size until it doesn't, crews can quickly become panicked. The chartplotter will do the maths on the closest point of approach, but if that picture only resolves five or ten minutes before it matters, there’s little room for error. Watching a closest point of approach shrink towards a few hundred metres and trying to decide whether to call the ship, alter course, or just hold on and trust the numbers is not fun.
The Problem With a Five-Mile Warning
Traditional VHF AIS in certain conditions can have an effective range as low as roughly five nautical miles. That sounds workable until you run the closing-speed maths. A yacht cruising at 10 knots meeting a container ship doing 25 knots head-on leaves roughly 8.5 minutes to spot the threat, make a decision, and act on it. In the middle of the night, at the end of a weary four-hour watch, that's not a generous margin.
The Solution
It’s this gap that a newer category of AIS technology has been built to close. Over the Horizon AIS (OHA), a satellite-fed system from marine weather forecasting company PredictWind, takes the same live vessel traffic picture and extends it out to 300 nautical miles. AIS targets can then be tracked on the chartplotter or by using the PredictWind app.
What Do I Need?
Accessing Over the Horizon AIS requires a Professional level PredictWind subscription, paired to a PredictWind DataHub if you want the data fed directly to your chartplotter. Through the DataHub, AIS data is obtained via Starlink, 4G/5G cellular, or another satellite connection and converted into a format the boat's own instruments understand. It’s fed straight into the chartplotter or a navigation app over Wi-Fi. Run the same closing-speed calculation at 300 nautical miles instead of five, and that 8.5-minute warning now stretches to roughly 8.5 hours.
It’s designed to work with gear sailors already have, PredictWind lists compatibility with most of the major chartplotter brands cruisers are using, including B&G, Raymarine, Garmin and Navionics, as well as popular navigation apps like OpenCPN. For most boats, that means the extended range simply appears on the same screen the crew already watches, rather than requiring a new one. If you don’t have a DataHub, but you have the PredictWind app on your phone or tablet with a Professional subscription, you can access it there as well.
What Over the Horizon AIS Provides
The practical difference that extra range makes is less about any single dramatic save and more about what it allows a crew to do differently, day to day. Fishing fleets and congested shipping lanes along the route can be spotted and planned around well in advance, rather than discovered at close range. Watch schedules can be built with actual knowledge of when traffic is likely to be heaviest, instead of a rough guess. And because the picture is viewable on several devices at once rather than a single fixed unit, a crew effectively gains a backup if their onboard AIS receiver ever fails, no small thing a thousand miles from the nearest chandlery.
Perhaps the least glamorous benefit of this technology is also the most valuable. Imagine being off watch, trying to sleep but you can’t quite relax. Maybe a new crew member is on watch, or your partner is not the most confident using your new chartplotter. Instead of rousing from your bunk, you can just pull out your phone, open the PredictWind app and check the AIS in seconds.
A skipper who can see that the next vessel of concern is genuinely hours away, rather than wondering whether something could appear out of the dark in the next ten minutes, can actually rest when they should be resting. Fatigue is one of the most persistent and underrated hazards of ocean sailing, and any system that gives a crew back a few hours of uninterrupted sleep is a genuine safety upgrade.
A Tool, Not a Replacement
None of this is an argument for pulling the hardwired AIS unit off the boat. PredictWind is explicit that OHA isn’t a substitute for a vessel's own AIS transponder or receiver, it's designed to work alongside existing equipment, serving as a reliable backup if the primary system ever fails.
More Tech?
It can be easy to think that this is just another piece of tech that you don’t need on your boat. Whether OHA counts as “extra redundancy” or “a critical safety system” rather depends on how close that container ship was going to pass and most sailors, having once had that experience in close quarters at night, won't particularly want to find out again.
As this season’s fleet of Atlantic crossers prepares to leave the Canaries, it’s a reminder that the biggest advances in ocean safety aren't always about new gear bolted to the deck. What this technology strengthens is the amount of time a crew has to make a decision, and in offshore sailing, time is very often the entire safety margin. Sometimes it’s about simply being able to see further into the dark ahead.
Find out more about Over the Horizon AIS.