AIS is an acronym for Automated Information System. A less descriptive name I could not have invented, but it is a fantastically useful thing. Here is the description of two interactions between large ships and small yachts sailing at night, and what happens…
The skipper is asleep, and the crew on watch sees ahead lights just breaking over the horizon. As they were instructed, they wake the skipper immediately. Since the lights have appeared ahead of us, we can assume they are sailing in our general direction at something like 18 knots, and we are going toward them at 6 knots, closing speed of 24 knots. We know from previous experience that ship lights like this appear over the horizon at about 6 miles away. We have at most 20 minutes to decide if there is a risk of collision, and then decide on what to do that will not make things worse, and then execute whatever evasive actions we think best, in the dark, all while just awake from a deep sleep. Very stressful.
Now in a world with AIS, the situation looks like this: the crew sees an icon appear on the chart plotter at a distance of about 30 miles. They touch the screen, and information appears. The other ship’s name, destination, course, heading, speed, length, beam, draft, current rate of turn. Everything except how the Captain takes his coffee. Most helpful is the Closest Point Of Approach. Our plotter has taken course and speed from both boats and calculated how close we will get at the closest. The crew can immediately look at that display when the ship is an hour away and decide if the skipper needs to be awakened. ALMOST all the time there will be plenty of room even at the closest, and sleep need not be disturbed. The skipper likes this.
Of course, we still need to look around. It is possible that a ship has a malfunctioning system, or is small enough that AIS is not required. But the vast majority of interactions between ships are now so much easier, less stressful, and safer.
On the boat today, the wind is 20 knots from the NW, we are close reaching at between 5 and 6 knots, on a straight line course for our first anticipated landfall 565 nautical miles away in the Channel Islands. It might not be our anticipated destination, but the sailing is good, the weather is good, the boat and crew are good. Life is good.