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Old 30-08-2015, 07:24   #1
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Join Date: Sep 2014
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Boat: Peterson Islander 40
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AIS The system and my installation

AIS (Automatic Identification System) is an electronic apparatus that transmits and receives information between vessels and land bases. It uses VHF. It gives your position, heading, speed, COG (course over ground) and receives the same from other stations within range. It also calculates CPA (Closest Point of Approach.) How close another vessel will pass you and when. If a collision is imminent it also has an alarm system which you can set for your own considerations. There are other 'whistles and bells' such as memory cards and Wi-Fi etc.

I purchased an Alltech class B transponder on-line for about US$500. You also need to buy a compatible GPS antenna. I purchased a robust exterior mushroom type $130 which fastens to the rail. You can buy the interior 'puck' type much cheaper. Then you need to connect it to a VHF antenna. There are two ways of doing this. You can buy an electronic splitter $200. This allows the AIS and Your VHF radio to use one antenna. Or you can install a second VHF antenna $100 with cable. I chose the latter for two reasons: I now have two VHF antennas on board, and one less piece of electronics to go wrong! I mounted the second antenna aft on my solar panels, and connected my VHF radio to it, using the original antenna on top of the mast for my new AIS so as to get maximum range. I thought about the compromised range for my VHF radio but then thought about its usage. Usually short. Port Control. Ship to ship at anchor. Anyway, I can always physically change them over if needed. Next is 12V power and connection to my laptop. Pretty easy. Red & Black? It came with a USB cable which plugged straight into my lap top. It also has a data cable for NMEA to connect to the chart plotter if you have one. You can also fit an optional switch so as to turn off the transmitter and receive only, which I did.

Now you need a MMSI number. Depending which country your in, it will be issued through the appropriate Government body, which can easily be found on-line. In Australia, I had to provide proof of a current MROCP (Marine Radio Operators Certificate of Proficiency) before they would issue me one. I also had to apply to Alltech Marine for an activation number. This I did on-line. I received both within twenty four hours.

It's then simply a matter of loading the driver and software, either from CD or download, enter your particulars, and you're up and running.

I use a laptop with Open CPN. The GPS antenna connected to the AIS will give you your position so I only have two cables on my chart table. One to power my computer, the other USB directly to my AIS. It draws surprisingly little current. 300ma. That's less than a third of one amp hour.

Class B AIS transmits on 2 watt's of power, and they say it only has a range of 7 miles. Maybe with an antenna just above sea level this is true, but my antenna is at 60 ft. I have spoken to other vessels who are easily receiving my signal 15 to 20 miles away.

In the name of safety...Happy sailing.

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Old 30-08-2015, 10:42   #2
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Re: AIS The system and my installation

Good report, thanks!

In the USA we aren't allowed to program our own MMSI (also vessel name if I recall correctly). Instead, the dealer or certified(?) technician has to do it for us. This is supposed to reduce the chance of misprogramming, or so they say.

As for Class-B range, the antenna height does make a difference. A rail-mounted antenna probably gets six miles as a general minimum, and a mast-mounted antenna more like ten miles. These are minimums, based on my personal experence (your mileage may vary.) You can often get 20 miles or better. Occasionally you will see hundreds of miles. Extended propagation is fun, but six miles will still do the job.
Paul Elliott, S/V VALIS - Pacific Seacraft 44 #16 - Friday Harbor, WA
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