AIS comes in three basic forms. A transponder not only tells you where other similarly equipped vessels are, but also tells them where you are. All commercial vessels operating in North American waters are required to have AIS transponders that broadcast their data on frequencies 161.975 MHz and 162.025 MHz (old VHF channels 87 & 88). AIS receivers only tell you where transponder equipped vessels are, and they. come in two versions, dual channel and single channel. The dual channel unit monitors both frequencies simultaneously, whereas the single channel unit monitors both channels by switching back and forth. Transponders cost several thousand dollars, dual channel receivers about $500, and single channel receivers less than $200. AIS is a black box requiring a separate display. It streams NMEA 8013 data at 38,400 baud, so most chartplotters less than 5 years old are likely to be able to accept and translate the data as an overlay on electronic charts, but check with the manufacturer to be sure. Similarly, most recent computer-based electronic chart programs will do the same thing, as will Sea Clear II, a a free download from http://www.sping.com/seaclear/  contributions gratefully accepted. I decided to add an AIS receiver for three reasons in increasing order of importance. The first, to be honest, is simply because it's the gadget du jour; the second because we boat in an area in which islands, trans-pacific ships, and large fast ferries abound; and most important, my wife really hates meeting and being waked by them in blind passages. Transponder versus receiver? I concluded that if I know where the big guys are and what they're doing, I do not need to incur the expense of a transponder. The tougher question was a two channel or single channel receiver. There is such a relatively small difference in performance between them that I opted for the much less expensive single channel unit. I have Garmin 2010C chartplotters at each helm. Unfortunately, a call to Garmin Support eliminated them as potential AIS displays. However, I also run Nobeltec Max Pro Admiral 9.3 on a new HP laptop, and a call to Nobeltec Support confirmed compatibility. However, the tech didn't mention the problems associated with newer laptops that don't have serial ports and come with VISTA. With the cost of a plain vanilla SR161 now well below $200, it was an obvious choice, and I purchased everything I needed from a local marine electronics shop. That decision also delivered the benefit of conversation with Bob, the owner, and information that saved at least some aggravation. The small plain box contains the AIS unit, a power cord, a serial cable, and a basic manual that was written for someone with a bit of technical knowledge. Fortunately, none is necessary. AIS uses old VHF channels 87 and 88. The SR161 manual states that the VHF's radio's antenna can also be used by the AIS receiver with the addition of a splitter, but no one in the business recommends it. Bob also told me that while a VHF antenna  cost of a good 8 footer is about $125  works fine, he usually supplies a high quality ss wire antenna tuned to the AIS frequency for $50. (Basically, he trims about an inch off the bottom of the stainless steel whip.) He also noted that the antenna connector on the SR161 does not accept a standard VHF lead, and he provided the adapter. Finally, with everything in hand, it was off to the boat to do the install. Basically, it's mount the antenna, mount the receiver as close to the display unit as possible, run the wiring for antenna, power and data cables, and plug everything in. I wonder why the SR161 comes with a serial cable, since newer laptops no longer include serial or parallel ports. I bought a DB-9 serial-to-USB adapter cable from Radio Shack for $30. Didn't work because no VISTA drivers were available for it. Took it back and bought one off the Internet for $6. It came with a VISTA driver, but performance was intermittent. Finally did what I should have done at the outset, and bought one from Bob and all was well. With everything connected, I brought up Nobeltec on the laptop and ran the GPS Wizard from the Tools / Options menu. A note here: be patient and let the Wizard do its thing for a few minutes. My first attempts were unrewarded. When it found the GPS and seemed like nothing else was going to come up, I canceled too soon. When I finally let the Wizard continue to run, it also found data on another port, but showed an error message. I noted the port number, canceled this scan, too, then used the Options menu to configure that port by increasing the baud rate to 38400. (A key factoid noted in the manual and also supplied by Bob.) I ran the Wizard yet again, and this time it found the AIS receiver. I ticked the 'Apply' box, went back to the main display, and was pleasantly surprised to see several yellow AIS icons displayed on the chart. (The exact display will depend on the software program. A friend's chartplotter shows them in gray.) As others have pointed out, with AIS more is not necessarily better. AIS targets quickly clutter the display, and could easily overwhelm it. Moreover, many vessels broadcast even when tied up. The fun of seeing far-off vessels quickly dissipates in favor of information on the movements of ships in a limited region, and the software in most navigation programs lets you define the area for which AIS icons are displayed. Is AIS a worthwhile addition? You bet. Not only does it supplement radar by seeing around corners and behind obstacles, it also plots each target's course and sounds an alarm when a collision is a possibility. Plus, my wife likes it. Cheers, Garrett

Garrett Lambert <garrett.lambert@gmail.com> writes: >AIS targets quickly clutter the display, and could easily overwhelm >it. Moreover, many vessels broadcast even when tied up. The fun of >seeing far-off vessels quickly dissipates in favor of information on >the movements of ships in a limited region, and the software in most >navigation programs lets you define the area for which AIS icons are >displayed. Just a quick FYI on this. Using Nobeltec you can also filter the AIS targets, so (for example) you might choose to ignore targets that have a Closest Point of Approach greater than 2 miles. I do this and find it helps a great deal. Scott Welch Product Manager, Open Text Collaboration Solutions Group www.firstclass.com "Things turn out best for people who make the best of the way things turn out." - John Wooden