Is AIS in the house?

hardee · Posted: Sat Dec 14, 2013 3:23 am Post subject:

Another thread that has considerable about AIS and the Standard Horizon 2150.

http://www.c-brats.com/viewtopic.php?t=20861&highlight=

Alexander · Posted: Sat Dec 14, 2013 6:22 am Post subject:

I must qualify my last post. In the free version there is a 5 min refresh delay but there are pay versions with much less delay and more info. I don't have any experience with the pay versions. There is a companion app called IAIS the transmits your (Cell Phone's) position and it will show your position on real AIS receivers as well as the Marine Traffic app. It is also free and works well. We have used it for over 1 year.

thataway · Posted: Sat Dec 14, 2013 12:23 pm Post subject:

Alexander,
I may have not made my point clear. It is not the lack of cell service of your boat. The "holes" in the various apps, are places where there are no volunteer listeners. If you watch boats in many areas, especially in the less populated areas of the ICW--they just don't have any AIS readings for long segments of the coast line. That is because there are not any people who have put in an AIS receiver, antenna and who dedicate a computer to sending the AIS reports to the server for the APP.

Regards,

ssobol · Posted: Sat Dec 14, 2013 12:36 pm Post subject:

hardee · Posted: Sat Dec 14, 2013 1:11 pm Post subject:

thataway · Posted: Sat Dec 14, 2013 1:22 pm Post subject:

Today true AIS receivers are inexpensive--and the cost of AIS B has come down very significantly--less than radar. It is not for everyone. But if you are in high commercial traffic areas or in low visability situations (even after dark) it will give you invaluable information, and is a great safety device.

mailbox101 · Posted: Mon Dec 16, 2013 12:34 am Post subject:

Hi Alexander, and welcome aboard!

Although cloud-based AIS is a fun hack, it really isn't yet developed to the point that I would care to count on it as primary navigational or safety equipment.

Last summer, on our trip up the coast, I played with land-based AIS monitoring networks a bit, comparing it to the results obtained by the class B transceiver on-board. Although I was expecting to find gaps in coverage in the rural sections of the coast, I was surprised how many gaps existed even in fairly urban and populated areas. As we have been from San Francisco to Two Harbors several times, always have our AIS on, and are usually within radio range of the shore, a quick historic search for WDF(remove this spam reducer)4868 will show which coastal areas are covered, and how much is not.

Satellite based AIS is starting to come along, but cannot transmit at this time. A major issue that has to be overcome is that the AIS transmitting protocol, which was developed in order to prevent ships that are within range of each other from transmitting at the same time, was not designed to have the number of ships as that are within range a satellite. The ship based units that are out of sight of each other can, and do, transmit at the same time as each other, thus creating a digital mess.

Given how slowly marine users and leadership have adopted new technology (even a VHS radio is considered voluntary on most recreational boats, and some still don't have them) I suspect that a comprehensive, transceiving, cloud-based AIS is still many years off.

David

Alexander · Posted: Mon Dec 16, 2013 6:46 am Post subject:

As I stated in an earlier post, I don't use (or need ) this app for navigation. It's main use to me is to show my position to my son with whom I always share my cruising plans (and vice versa), . It provides a position and track so he always knows where we are in case of trouble. For my phone to transmit my location it does need a cell connection but does not need wifi. When we leave cell coverage the position shows last contact position and refreshes to new position as we re-enter coverage. It triangulates using towers so when offshore and in contact with a single tower it will show the tower position. A last known position is much better than "whereabouts unknown" if help is needed.
With a 5 min refresh rate, if you have coverage, this app shows ships of interest way before they become a threat and it shows course and speed.

Given the fact that most boats on the water don't have AIS I don't consider AIS as a reliable defensive safety net when compared to radar and an attentive helmsman. It is a useful tool and it will likely get to be more useful but only a tool.
A good discussion thanks

thataway · Posted: Mon Dec 16, 2013 4:02 pm Post subject:

Alexander · Posted: Mon Dec 16, 2013 5:56 pm Post subject:

Hi Bob , I agree with your points. My discussion was relevant to the free apps not real AIS. I do not use the Apps for my nav tool while underway. My area (Stuart,Fl.) includes 98% private vessels and very little fog problem and mostly daytime ICW travel. I have not used real AIS so I defer completely to your experience with it as to it's usefulness.
Real AIS does show up on the app and it has world wide coverage and specs and pics of vessels as well as course and speed. By zooming out you can watch vessels as many miles away as you want and track their course and speed long before they are near your position. It does have some value. I just don't need it for my normal travel, I do transmit the signal for my son but I don't run a laptop while underway.
My son keeps tabs on us using his Samsung Galaxy 4 on his 4g phone network in Boston. It is only on internet but wifi is not needed needed.
My error on the gps issue. We don't loose location anymore but we used to. Important to know that the position generated with this app IS NOT seen by real AIS systems on other vessels.

colbysmith · Posted: Mon Dec 16, 2013 7:26 pm Post subject:

I'm new to this thread, and guess completely clueless about AIS. But from the quick review I made of this thread, it sounds like it could be useful tool on the Mississippi, perhaps on the Great Lakes, and also in the San Juans if I make that trip next summer. Sooooo, any recommendations for inexpensive stand alone units? Or recievers/transponders that would be able to connect up with an old Pathfinder radar or newer Garmin GPS? Colby

thataway · Posted: Mon Dec 16, 2013 7:39 pm Post subject:

Many of the newer radios from both Standard Horizon or Icom have the AIS built in. It just takes a couple of wires connection to the chart plotter and you have the AIS overlaid on the charts. The older SH Matrix 2100 is about $200, and the slightly easier to use 2150 is a little over $300.

There are cheaper ways: Digital Yacht AIS 100 is about $165. Miltech has a number of receivers for in the $200 range.

I happen to have the older Standard Horizon Matrix 2100--a couple of wires to the Garmin chart plotter, and hit a few menu buttons, and you are ready to do. This has the radio receiver, plus using the radio's antenna.

colbysmith · Posted: Mon Dec 16, 2013 10:35 pm Post subject:

Thanks. What about transmitter. Do any of those radios transmit AIS also? The 2150 sounds like a nice unit, but since I have both an older Ray Marine Pathfinder Radar, and a newer Garmin GPSMAP, I would think it would be easy enuf to connect the older 2100 to one or both of those. (I am concerned if the radar would communicate with the 2100. As of now, it will not connect with the new Garmin. Either of these have a larger screen than the VHF 2150 would have. Also, I see a "class D" or a "standard" model of the 2150. Is there a difference or is it just advertising? Colby

hardee · Posted: Tue Dec 17, 2013 5:07 am Post subject:

thataway · Posted: Tue Dec 17, 2013 4:53 pm Post subject:

As for transmitting--there is Class A--which is what commercial vessels use. These will begin at about $2,500. The Class B, which has a lower power transmitter, and less frequent transmissions starts for a very basic unit at about $500. The one I recommend is what Harvey is considering--the Vesper Watchmate 850--about $800 or a bit more. This has a 5" screen for viewing positions of the various vessels, or the information about a single vessel or several vessels. It also has a built in GPS chip and antenna, so the only hook up is to an antenna and power. You can also have the AIS on your chart plotter. My preference is for a separate specific AIS antenna, But you can consider a good quality splitter.

As for Radios--I like to have two VHF radios, so I can monitor two different frequencies--there are some advantages to that over a dual watch or scanner. So I have a radio which has the built in AIS receiver. My AIS is overlaid on a 5" Garmin (540) receiver. I have a 740S which I could overlay the AIS on if necessary. The chart plotter has to have a high speed input port--38400 baud.

I certainly agree with Harvey about the rapidity of the CPA determination. It is virtually automatic and is easily updated. I come from the school of taking bearings or using Radar plotters to determine CPA. MARPA requires a gyro-rated heading indicator in most cases. Although radar overlay can be done on chart plotters without an accurate heading indicator it does not work at zero speed, and it is not as accurate as when utilized with a very accurate heading indicator.

I think there are too many issues to allow most of the AIS receiving radios to give an accurate picture on the Raymarine Pathfinder Radar (I believe it does not have the 38,400 baud NMEA input port) The Garmin will work fine as long as it has the 38,400 Baud input. Class "D" means that it is a dual channel receiver--with a dedicated receiver on channel 70 for DSC calls.

AIS has two channels: AIS 1 161.975 MHz, and AIS 2 162.025 MHZ. These are at the upper end of the Marine VHF spectrum, and that is why I recommend an antenna tuned specifically for AIS. Your VHF channel 16 is at 156.800 MHz. You want to have your VHF antenna turned for the min SWR at 156.000 MHz to 157.500 MHz. As you can see the AIS is some distance above this, and will often have a high SWR (lower effective radiated power) with an antenna tuned for 156.800 MHz (This will only be really important with a transmitting AIS unit.)