AIS Information

[Rick D]

I have been using my AIS when at the boat to get familiar with it and I'm pretty impressed. My slip is located in the midst of a huge port so I have lots of activity available to monitor. I mentioned that I used a high-gain rubber ducky scanner VHF/UHF antenna attached directly to the AIS receiver. I am getting eight miles range with it, so I'm not going with an antenna splitter or dedicated VHF antenna until I test it offshore where I would expect even better performance. Eight miles would be plenty if its reliable. However, the data transmitted from commercial shipping is really spotty. Lots of them have not inputted their size or draft. Maybe a third have not inputted their name and call signs. Yesterday, I even saw a tanker that was 'moored' moving at six knots!It is still an excellent safety supplement and an excellent value too which is more than you can say for some marine navigation gear. But, the level of compliance with the data is pretty sloppy.What have the rest of you found? What about AIS range?Rick D.

 

[RichH]

You probably want to put the AIS antenna

or use the splitter to your masthead VHF antenna, as when your boat is in the bottom of the trough of a large set of ocean swells ... that rubber ducky isnt going to have very much range (line of sight).

 

[Buck2796]

Rick,

I installed mine in June. I use an antenna splitter w/ my masthead VHF antenna. Works fine. If you read my log post a few weeks ago; I commented that I was getting contacts as far as 40 miles away when offshore. I find it to be not only fun and informative, but a wonderful help both day and night at lessing the stress of collision avoidance. It's great to know about vessel traffic long before you can see them visually or on radar. And to see them presented on your computer or chartplotter screen where they are and with heading/speed line indicators (and even wake indicators) is awsome! ! I have also found the same spotty data imputting over on this side... I assume it is mostly laziness on the part of the ship crews. At least their transponders are automatic and you still get their speed and position (and therefore collision avoidance info) from all transmitting contacts.Unfortunately Navy ships and (some of the time) Coast Guard ships do not transmit data (for obvious reasons). Around Norfolk they constitute a LOT of traffic. Even so, AIS is (IMHO) a great thing. Much better than radar for collision avoidance (at least for those vessels transmitting it).As more (non commerical) vessels install transmitters (and I suspect it will be offered within a couple of years inexpensively on almost all boats over, maybe ?, 40') a "double edged sword" will begin to occur. Even more effective target presentation, but too many contacts; causing losts of clutter and requiring alot of filtering of one sort or another.I guess we'll see

 

[Dick]

What brand of receiver did you folks purchase?

After the first of the year when I change over to an E120 I'm adding it to our boat. I was considering bitting the bullet and buying a transponder, but I doubt big ships really care where I am in relation to them.

 

[Rick D]

Smart Radio AIS Receiver, Dick... (revised)

...for me, but I use mine with my laptop, not my chartplotter. I think you'd need to get Raymarine's own unit to interface with the E120; see the link. By the way, Dick, these units are receive only; they do not transmit information regarding your vessel.Rick D.Sorry: I forgot the link the first time

 

[Buck2796]

I Think

I have the same receiver that Rick does ... Milltech Smart Radio SR 161 Receiver (and I bought their antenna splitter). Link ... http://www.milltechmarine.com/products.htm Also, like Rick, I use a computer not a chartplotter... I have a small desktop running Nobeltec Vis. Navigator software; the more recent versions of which support AIS.

 

[Dick]

Thanks guys. Milltech seems to be the

most popular. They do interface with the E-120 through the autopilot interface box. I have 2 friends with the Raymarine receiver and E-120s and they are in the process of returning them and will install a Milltech. Seems the Raymarine units have, at times, a very long delay in displaying ships. They have talked to Raymarine and they acknowledge a software problem that will fixed with an update sometime after the first of the year.

 

[Don12364]

Spotty Ship Transmissions

Rick is right. The commercial guys came to AIS hurriedly and reluctantly. Also their equipment is not as good as ours and quite often they have little or no idea of what they are transmitting. They overlay it on RADAR rather than a vector chart - which most of them do not have - and so loose much of the benefit of AIS.However, the vital pieces of data for us are automatically transmitted and this includes the Lat & Long, COG, SOG Rate of turn and MMSI. This means that the ship's navigation officer cannot influence this data. I don't mind them forgetting to update their destination and their draft, which changes depending on whether they are laden or not, but their position is (almost) always spot on.Regarding Naval vessels, they are 'excused AIS' but they recognise its importance. At a Royal Institute of Navigation lecture here in England in 2006 I asked the Royal Navy's Fleet Communications Chief (the top nebby!) why, in peacetime, they do not transmit AIS. I said I didn't fancy meeting a 'stealth' aircraft carrier one foggy night. He agreed and said their policy was to fit AIS.Meantime I take some comfort from the fact that, unlike the merchantmen, they man their bridges fully and there are serious penalties for defaulters. If a small yacht could be seen by a navy ship I can reasonably expect that it will be seen - and - presumably - they also know the Colregs!

 

[Bryce22345]

AIS

I have a Si-Tex dual channel interfaced to a Raymarine E-120. substantially less money that the Raymarine unit and has been quite reliable and interfaces directly to the E120. also have RNS so AIS is available on both units. we have a fair amount of commercial traffic here in the Boston area so it been quite interesting watching the traffic. agree with Rick that a lot of commercial vessels aren't updating most of the user input info for the AIS but the "auto" information is quite accurate, i.e. lat/long, SOG course etc. However the Coast Guard here in Region II has become more diligent in warning commercial vessels to keep the info updated. we'll see what actually happens. since AIS is VHF transmissions, 8-10 miles range is pretty nominal. like any VHF transmission a "skip" from further away is always possible.Bryce

 

[Buck2796]

Bryce

The height of a mast head antenna on a ~40 sailboat is 50-60 feet.The height of the antenna on a large container ship is probable 100' or more.Using 1.17 x sq root of height for horizon distance; and adding them together gives a nominal VHF range of ~ 20 nm for an AIS contact betwen the typical sailboat and a large ship.At my slip in Little Creek I was routinely getting AIS contacts out to 20+ nm.Offshore, I occasionally had targets displayed out to nm ranges of up to upper 30's. So skip apparently can allow as much as twice nominal range? ?