Class B AIS

[stadjer]

I have an Em-Trak B100 on my boat. Works like a charm. On the boat it is connected to a VHF antenna splitter and via USB to my laptop.

I think it's relatively inexpensive and worth every dollar in being able to see and be seen on the very busy North Sea.

[MarkJ]

Mark,

iNavx says it only uses AIS off the internet when you are connected to WIFI or Cell.

See the screenshot below.

Are you SURE yours works using your AIS transponder?

[MarkJ]

Originally Posted by jannw

don't overthink it ... get the vespermarine xb8000

Thats great analysis.

[colemj]

Originally Posted by Dockhead

I would be really concerned with a transmit range of only 3 or 4 miles, which I think is unacceptable. Ships plan their maneuvers much further out than that. I think 10 miles is the ragged edge of acceptable transmit performance.


Transmit range for my setup is extremely variable and for reasons I don't fully understand, but usually more than 25 miles.

3-4nm is low for class B, but 8-10 is good. If you are transmitting class B more than 25nm, then that is more of a function of atmospheric conditions or a very high receiving antenna. That isn't a normal expected range for class B regardless of the quality of installation.

There is no functional difference from VHF, so its range should be the same as a 2W VHF transmission from wherever the antenna is located. Most handhelds transmit in that power range using a 3dB antenna and don't get much further than 5-10nm.

The single advantage of a separate antenna is that the antenna can be tuned to the specific AIS frequencies while leaving your VHF antenna tuned to CH16. Right now, we have a SWR of 2.0:1 on the AIS frequencies using our VHF antenna. If I trimmed the antenna, I could expect to have an SWR close to 1:1. Practically, however, there would not be much gain doing this.

Mark

[J Clark H356]

MarkJ:

I have a DigitalYacht IAIS that is usb to my laptop (running RayNav 6.0 and wireless to my IPad. I use INavX to receive on the IPad. There is no other way I can get AIS on INavX that I am aware of.

I looked at the Siltek link and it is possible with wifi or cell to connect to the Siltech free server for some locations. I didn't connect up through INavX but read MarkJ's image above or go to INavX help and you should be able to receive limited AIS.


Sent from my iPad using Cruisers Sailing Forum

[colemj]

Originally Posted by MarkJ

Mark,

iNavx says it only uses AIS off the internet when you are connected to WIFI or Cell.

See the screenshot below.

Are you SURE yours works using your AIS transponder?

I am not using iNavX, but have used it elsewhere and am sure it is not getting AIS off the internet. Here is what they say in their website FAQ:

Does iNavX™ support AIS receivers and transponders?

Yes via TCP/IP. Targets are plotted on the chart with real-world scaling. An AIS Transponder can be used to provide own position, speed and course to iNavX™. SART and NavAids are supported.

They then mention in another FAQ that if you do not have an onboard AIS transponder/receiver, you can connect to the internet using the Sciitex server.

They give specific instructions in their user manual for connecting to various brands of AIS transponders with wifi capabilities.

Mark

[monte]

We have the Raymarine and it works well with USB to opencpn and the plotter, don't really use iPads for navigation. On range, ours picks up ships around 15 miles or so with the masthead antenna and VHF splitter. I don't think 5M range is anywhere near enough. Often we are making crossing decision 10M out and contacting ships on VHF to confirm starboard to starboard or passing ahead or behind crossings if that's the case. 5 miles would only give you last minute data and course alterations should probably have already been made by that stage

[sck5]

I have a garmin ais on my boat because i already had a garmin plotter. It is the greatest thing since sliced bread. Even though the antenna is on the stern rail it sees and is seen at least 20 miles away. That is a good thing on Chesapeake Bay when you really do want to know what freighter traffic or tugs are coming up or down in plenty of time to give them the room they need. I really wouldnt want to only see them when they are 5 miles away. At 25 knots plus closure rate that doesnt give enough time to maneuver, or at least not as much as I would need to stay relaxed. And that is the goal right? No more wondering what the hell those lights out there are doing when going up or down the bay in the middle of the night.

I also have been on other peoples' boats with RM units and standalone units. They all seemed to work just fine. I have never heard of anyone having a problem with them. They really arent very complicated.

[robert sailor]

I'm not sure where some of you fellows get your range reference from but we have checked at least a dozen friends for AIS range and the best we ever saw was around 6-8 miles and most were in the 5-6 mile range and a few slightly below 5 miles so when I hear 20/25 miles its starting to fall into that unbelievable range. Most class B manufacturers suggest a max range of around 10 miles. I know on certain days that 25 watt VHF will skip and you can send and receive sometimes much further than the normal 25 mile range so I'm sure that the odd person might get a long range hit on their 2 watt AIS transmitter but its hard for me to believe this is normal.

[Dockhead]

Originally Posted by colemj

3-4nm is low for class B, but 8-10 is good. If you are transmitting class B more than 25nm, then that is more of a function of atmospheric conditions or a very high receiving antenna. That isn't a normal expected range for class B regardless of the quality of installation.

There is no functional difference from VHF, so its range should be the same as a 2W VHF transmission from wherever the antenna is located. Most handhelds transmit in that power range using a 3dB antenna and don't get much further than 5-10nm.

The single advantage of a separate antenna is that the antenna can be tuned to the specific AIS frequencies while leaving your VHF antenna tuned to CH16. Right now, we have a SWR of 2.0:1 on the AIS frequencies using our VHF antenna. If I trimmed the antenna, I could expect to have an SWR close to 1:1. Practically, however, there would not be much gain doing this.

Mark

I think that there is a functional difference between AIS and FM analogue voice VHF -- AIS is digital with robust error correction. It should work much better over longer distances with the same power as a voice FM/VHF signal.

But I have had a "weak but readable" signal report from Solent Coast Guard from 60 miles -- using only 1 watt of transmit power on my regular fixed VHF (an Icom M604). With another moderator of this forum as a witness. Antenna and cabling make just an enormous difference. It's a good antenna -- Shakespeare Galaxy silver plated internal dipole antenna, and RG213 cabling, and this is where it shows itself.

So I don't think it's amazing that I get 20 or even 30 miles of transmit from a lower, but also good antenna and good installation, using AIS. Class "B" AIS emissions are FSK or GMSK, transmitted at 2 watts. That's a lot of power for a FSK emission. With a reasonable antenna and cable installation, you should be able to get out to any ship whose antenna is in line of sight with yours, no matter how far away it is, and to ships even further than that. I think anyone getting less range than this is probably held back by the antenna and/or cabling, not the antenna height.

[donradcliffe]

I used a separate pushpit VHF antenna for the AIS, and mounted it next to the VHF so I could easily switch to the masthead antenna if I wanted to. One of the reasons I installed the pushpit antenna was that it can also be used as a good emergency antenna for the VHF if I ever lost the mast.

I found that with the pushpit antenna I could pick up Class A transponders on ships at 10 to 15 miles, versus 12 to 20 miles (occasionally out to 100 miles) on the masthead antenna. With the pushpit antenna, Class B signal range was from 4 to 8 miles, while with the masthead it might be from 6 to 10 miles. With both Class A and B signals, a lot depends on where and how well the transponder antenna was installed--I saw weaker than expected signals from both types of transponders.

As the Class B transponder uses less transmit power, I would pick up ships before they picked me up. That was a good thing, as it gave the the option of adjusting the CPA before the ship watchstander saw me and made any course changes. I would much rather make a 0.5 mile CPA into a 1.5 mile CPA based on a ship holding course than have to worry about whether he is going to towards into my new course.

If you are going offshore, the Vesper units with radar display allow you to turn off your chartplotter and save a lot of power. If you are doing inland and coastal, having the ship's vector on the chart gives you more information, as you can see in advance where the ship is likely to turn.

We looked into using AIS with Inavx on an Ipad, but it required a $400 black box to convert the AIS signal to Wifi. With OpenCpn, at most it is a $20 serial/USB converter.

[donradcliffe]

Originally Posted by Dockhead

I think that there is a functional difference between AIS and FM analogue voice VHF -- AIS is digital with robust error correction. It should work much better over longer distances with the same power as a voice FM/VHF signal.

AIS is digital, but AFAIK there is no error correction--if one packet doesn't get received correctly, the system just waits for the next transmission.

[Dockhead]

Originally Posted by donradcliffe

We looked into using AIS with Inavx on an Ipad, but it required a $400 black box to convert the AIS signal to Wifi. With OpenCpn, at most it is a $20 serial/USB converter.

A much cheaper way to get AIS into an IPad is with the Simrad GoFree system -- works a treat.

However, the INavX implementation of AIS is very crude. At the opposite end of the scale is the brilliant OpenCPN AIS display. This is so good, that in hairy situations last summer I often went down to the nav table to monitor a developing situation in OpenCPN, rather than do it from my regular navigation system. Bit of thread drift, but the OpenCPN display shows you precisely what the relative positions of your ship and the target will be at any given time and, particularly, at CPA. The big electronics manufacturers should imitate this for our plotters.

[Sandero]

AIS B plotter for offshore is a good idea! Now all the data is being ported to the MFD where you have to split screens or has all sorts of repeaters.. all consuming power. For offshore having JUST an AIS plotter on duty makes sense and let the power hungry network sleep... Maybe.

They don't do many stand alone instruments that you can selectively turn on and off... or so it seems these days.

What say you?

[a64pilot]

Vesper does, seems only difference is the screen, and about $400. I think I'll stay with the Ipad when power is an issue and I'm turning stuff off, plus the $400 ain't chump change to me.