Voyagers embrace AIS

A 121

To the editor: We’d been picking-up commercial traffic on the radar since we closed within 200 nm of the Australian coast following a sloppy, 12-day passage from Efate in Vanuatu. We crossed the outer shipping lanes after making our turn west toward Cairns at Sand Cay on Diane Bank. Typically, when we see a ship pop up on the radar (which we fire-up every half hour or so to try and get as early a warning on approaching vessels as possible) we target it with the mini automatic radar plotting aid (MARPA) tracking function on our Raymarine E80. Although MARPA tracking will ostensibly give us a ship’s bearing, range, course, speed, closest point of approach (CPA) and time to CPA, the reality is that since MARPA is relying on data picked up by our radar signal and since we are rolling, pitching and yawing all the time, MARPA data fluctuates quite a bit, often not zeroing-in with much precision until we are too close for comfort.

Friends on other boats have been asking us for the last two years when we were going to install an automatic identification system (AIS) to complement our radar tracking and, until recently, we’ve made light of it saying that “a good pair of eyes and MARPA…plus some common sense” is plenty protection enough for us! The reality is that, because AIS data is a result of a signal sent by another ship and is therefore not altered by our movement, it is much more accurate than the MARPA tracking system and can be read reliably at a far greater distance. Of course, it relies on other vessels actually sending AIS signals, which is not guaranteed. Most commercial vessels are required to be equipped with AIS, but even those mandated to carry it can also (under certain conditions) turn off their AIS equipment at the master’s discretion. It’s therefore still very important to keep a sharp eye peeled and a close watch on the radar as well. But AIS sure takes a lot of the guess work out of tracking those vessels out there that are broadcasting.

As we contemplated our next passage over the top of Australia’s furthest north Cape York and heard from other cruising friends how much they loved their AIS systems, we finally broke down and decided to spring for one when we arrived in Cairns. It helped that our latest crewmember was arriving from New Zealand and she was willing to stop by Vesper Marine in Auckland on her way to the airport and pickup both the AIS and Vesper’s newly created AISWatchMate collision warning system which makes a nice duel package for about $840.

U.S. sailing friends, Jeff Robbins and Deirdre Schleigh, who arrived in New Zealand a couple of years ago aboard their boat Vesper, decided to take up residence and open up shop in Auckland after inventing the WatchMate system, developing a prototype, and then doing a good job beginning to market it globally. They’d told us much about its fine points including its alarm systems, target prioritization, filters and risk alert, as well as its clear, simple display monitor and low amp draw which allows us to run it constantly while sailing, something our more electricity hungry radar system prohibits. For more information, visit their Web site at

Our new crewmember, Georgina, (a hospice nurse desperately seeking some much-needed downtime at sea), arrived with the AIS receiver and WatchMate in her duffel, having successfully passed through Australian customs with no duty levied. We had the whole package wired and up-and-running within a couple of days with some good support from a local Cairns electrician.

AIS requires only a 12-volt power connection and a VHF antenna since it operates on two dedicated VHF frequencies (AIS1, 161.975 MHz and AIS2, 162.025 MHz). AIS uses these two VHF radio channels, where the information is transmitted in short data packages or slots in predefined and synchronized time frames. The dynamic information (position, speed, heading, etc) is transmitted in intervals from two seconds up to 10 seconds depending on the speed and maneuvers of the transiting vessel. Static and voyage-related info (vessel ID, ship type, cargo, size, destination, etc) is transmitted every six minutes or upon request from other units. We had the option of purchasing a transponder as well for a few more hundred dollars, but since we already use a Sea-Me transmitter which broadcasts an enhanced radar signal we decided to save a few bucks and by-pass this option. We did need to purchase an antenna splitter for about $128 in order to make use of our current VHF antenna.

Already, with only about three weeks use, we’ve found the AISWatchMate to be a great piece of safety gear to add to our arsenal. We had approached the top of Cape York on the inside passage up the Great Barrier Reef along the designated channel for vessels coming and going between the Arafura and the Coral seas. The WatchMate provides reliable, straight-forward data and advanced warning of collision to aid safe passage. It allows us to make course corrections early to “open up the window” as we approach oncoming ships. It’s especially helpful when there are a lot of targets out there. The prioritization scheme makes it easy to quickly judge which ships pose the greatest danger. Filtering of stationary targets also helps to unclutter the screen when approaching a busy harbor where many vessels may be waiting at anchor and pose no immediate threat.

Not only is it reliable, but it also serves as a great source of entertainment — like a new video game or TV set! We check it all the time and have fun gossiping about the stories it hints at. And mate Betsy has become the designated “ship tracker” on board where she often found the MARPA system intimidating and unreliable. She says: “I can even read it without my glasses!” a real boon for those of us in the over-50 market! We’ve found that the AISWatchMate gives us a very able and dependable third set of eyes in one of the world’s busiest and tightest shipping areas. We’ve also noticed that because we are able to call a ship by name, often provided with the AIS data, they are much more likely to answer us. We’re able to discuss crossing and course change options as needed, plus we’ve had many more enjoyable conversations with the commercial vessels we are approaching than in the past.

As we head north and west into more heavily-trafficked shipping areas, we’re very happy to have added this user-friendly “mate” to our set of electronic navigation aids.

—Nat and Betsy Warren-White live aboard Bahati, their 1988 Montevideo 43 built by Fred Scholtz Marine in Durban, South Africa.

By Ocean Navigator