Stay Safe WITH AIS
Why a collision-avoidance system is must-have technology.
Every year, the U.S. Coast Guard publishes its Recreational Boating Statistics—70-odd pages of tables, graphs, and statistics. Over the past five years, it has recorded nearly 9,000 boating accidents, more than 1,100 deaths, and almost a quarter of a billion dollars-worth of damage. You could see it as a depressing catalog of death and destruction, or you could say that it’s good that less than one hundredth of one percent of the 13 million registered boats in the United States are involved in a reportable accident each year. Or you could even say that the unknown number of unreported accidents and an unknown number of unregistered boats make nonsense of the whole thing. It depends, I suppose, on whether you look at a glass as half full, half empty, or whether you simply wonder what is in it!
But whichever line you choose to take, it’s pretty clear that the most common type of incident is a collision with another vessel, and that parting company from your boat—whether by accident or to go swimming—is the most dangerous kind.
When it comes to preventing disaster, there is, of course, no substitute for keeping your eyes open to what is going on around you and holding on when you do go over the side. But a relatively new electronic gizmo called AIS (Automatic Identification System) could turn out to be a key defender against both of the big-hitters of the accident league.
AIS is an automated communications system in which ships use two dedicated VHF channels to broadcast details of their position, course, speed, and lots more. All that information can be picked up by anyone with a suitable receiver and displayed on a suitable unit such as a radar or chartplotter. The system isn’t really new: the basic specifications date back to 1998, and it’s been compulsory equipment on most commercial vessels since 2004. It took the FCC (Federal Communication Commission) a long time to approve a cut-down specification for pleasureboats, but it finally did it in September 2008, and since then we boaters have been able to choose from three main types of AIS:
AIS A is the big-ship version; it’s too big and expensive to interest most private owners. But it transmits lots of information at intervals of a few seconds and cleverly reserves a time slot for its next transmission, ensuring that its messages will always get through to anyone with a receiver within range.
Receive-only AIS does what it says: it receives messages, but does not transmit any. It’s by far the least expensive of the three options and much better than no AIS at all. Depending on your choice of equipment it will tell you which AIS-equipped vessels are around you, where they are, and details of their courses and speeds. Most AIS receivers go several steps further than this: they calculate the closest point of approach (CPA) and the time to closest point of approach (TCPA) for each vessel, and sort them all into a list in order of the threat posed by each one. Linked to a radar or chartplotter, these units will display the AIS contacts on-screen, and linked to a radio, they will allow you to select and call any target without having to key in the vessel’s Marine Mobile Service Identity (MMSI) or call it by name.
AIS B is the recreational version, transmitting only the most important information, such as a boat’s MMSI number and her position, course, and speed, but at reduced power and at longer intervals. A subtle but important distinction between AIS A and AIS B is that AIS B transmitters can’t reserve transmission slots. Giving priority to AIS A transmissions means that—in theory, at least—there is a risk that AIS B transmissions might not get through. But although AIS B doesn’t guarantee that you will be seen by other vessels, it gives you a far better chance of being seen than a radar reflector—or than nothing at all.
But while the FCC was dragging its heels over accepting AIS B, international legislators were working on performance specifications and type-approval requirements for other AIS-based equipment such as AIS Search and Rescue Transmitters (SARTs).
An AIS SART is an AIS transmitter that is specially optimized for use in liferafts and lifeboats. A few dummy AIS SARTs appeared at shows and conferences last year, but now they’ve made the leap into reality, with the Jotron AIS SART (featured in last month’s column), expected to be available for about $1,200, anytime now.
The next step is almost obvious: make an AIS transmitter that is even smaller, so that it can be carried by an individual, rather than on a liferaft. Even before Jotron’s AIS SART is in full production, prototype personal AISs have already started appearing at boat shows. The fact that they are based on the same performance standards as AIS SARTs means that their batteries have to be big enough to provide 96 hours of continuous use. This might be a bit over the top for something that is intended primarily as a man-overboard marker and it means that the units are nowhere near as small or light as existing man-overboard alarms such as Raymarine’s Lifetag. Plus, at about $500 they are relatively expensive.
But the advantages are enormous. Rather than just telling the captain that someone has fallen overboard, an AIS man overboard (MOB) marker shows him where the casualty is, clearly displayed on the chartplotter and constantly updated, even if the person drifts with the current or tries to swim. And if other vessels join in the search, the MOB will show up on their AIS displays, too. Unfortunately, at 12 ounces, it’s not exactly a shirt-pocket accessory, but as most of that weight is the battery, there’s plenty of scope for later versions to be lighter once the regulations catch up with the technology!
This article originally appeared in the April 2010 issue of Power & Motoryacht magazine.