Class B AIS

[a64pilot]

I'll need one soon anyway but the thread about do you keep watch got me thinking again. I do want to xmit, not just receive.
I have no experience with AIS, I understand I believe it's capabilities and limitations, just no experience.
I think I want a stand alone unit that can integrate with a chart plotter etc., Bluetooth I think may be good as I'm beginning to use this Ipad more and more and think devices like it will become more common, not less.
I think I don't want one that can only display on a plotter, I'm the guy that likes to integrate things, but don't like single points of failure, I like stuff that can operate and display on their own.

Are my wants logical? If so what the best stand alone unit? I assume it need it's own VHF antenna, and it should be mounted on the mast head or can you use a splitter?

Any specific recommendations?

[Paul L]

Check the Vesper units. Decent price and lots of options. The Emtrex units are low cost and work well. You don't need a masthead antenna. Getting hits 40 miles away isn't required or helpful. ClassB xmit is designed for 5 mile range. An antenna at pushpit level works fine.

[jannw]

XB-8000 AIS transponder with built-in WiFi and NMEA 2000 Gateway

Buy that one!

Seriously.

and get the VHF splitter (although it seems to reduce my VHF power? not sure about that one yet ... still working on it).

Works like a charm, sends AIS out, distributes AIS, GPS, NMEA throughout the boat over wifi or USB.

[colemj]

We also have the Vesper XB8000 with the Vesper splitter. Works very well - our computer and iPad charting software gets their data by wifi. This unit integrates into a chartplotter by wifi, USB, NMEA0183 and NMEA2000 - take your pick.

Just a note: wireless connections will be with wifi, not bluetooth.

We don't have any practical attenuation on our VHF using the splitter. The specs are 1dB TX attenuation, and in another thread here was posted actual measurements of it showing <1dB attenuation in use.

I disagree with Paul on the distance point. I like getting vessel reports from far away! I also like increasing the distance we are seen as much as possible. But most of all, I like not having to disassemble the boat to snake another run of coax to the rail, drill a hole to bring it through and out, and find a place to mount the antenna where it isn't in the way of other things.

Mark

[MarkJ]

I thought you would have read the myriad of AIS threads?

I can't find any Class B AIS thats available that has Bluetooth at all. One has it but wont work on iPad.

I dont think any iPad aps use Bluetooth... I have iNavx, Garmin and Navamatics and none use AIS as far as I can see.

Spitters cost $250

A seperate antenna costs $70 plus cable $30.

A seperate antenna gives you redundancy.

I have Raymarine (Defender $729) as its USB, and, well, Raymarine. There are lots of others out there but, interestingly, I dont think theres any threads where people slag any particular brand. Once you get one and its got the features you want they seem to work.

You want a unit that can be used in as many of the things as possible. Mine will do a chart plotter (if I had one) at the same time as my PC and VHF.

Once you have one installed and working and go for a sail you will never want to be without one again. Gone are the days of seeing a ship and wondering where its going.

Beware: There are many nay-sayers who do not have AIS that for some bizarre reason don't want you to have AIS. No, they don't work on the moon and the ships of the desert dont have AIS and they will not stop you getting drunk, losing your virginity or healing Ebola.




Mark

[MarkJ]

Originally Posted by colemj

Works very well - our computer and iPad charting software gets their data by wifi.

Mark

What iPad software are you using?




Mark

[colemj]

Originally Posted by MarkJ

I have iNavx, Garmin and Navamatics and none use AIS as far as I can see.

Spitters cost $250

A seperate antenna costs $70 plus cable $30.

A seperate antenna gives you redundancy.

iNavx uses and displays AIS data. So does SEAiq and Navlink.

The small price difference (ignoring the cost of one's time and effort) could be a valid make/break decision between a splitter and separate run.

I don't understand the redundancy point - just carry a spare antenna and a coax pigtail if that is a concern. Unless your VHF and AIS are mounted very near each other, having two antennas mounted won't give practical redundancy unless you have already run pigtail connections from one to the other.

I have met several boats that have removed a stern rail AIS antenna because of poor AIS performance and gone to a splitter to the masthead with good results. I haven't met anyone yet who was dissatisfied with splitting their masthead antenna.

Mark

[Paul L]

Originally Posted by colemj

......
I disagree with Paul on the distance point. I like getting vessel reports from far away! I also like increasing the distance we are seen as much as possible. But most of all, I like not having to disassemble the boat to snake another run of coax to the rail, drill a hole to bring it through and out, and find a place to mount the antenna where it isn't in the way of other things.

Mark

Getting hits from a long distance while on watch might help defer the boredom, but its pretty academic. I don't get a lot of actionable info from a tanker traveling 13kts at 40 miles away.
There is an easy way to increase your AIS signal. Its called Class A and specifically designed for long distance xmitting. The Class B are designed for short distance, both to reduce cost and congestion. Seems reasonable to use the device as it was designed.
I have no problem with using a splitter. Less wire running the better. I just didn't agree with the OP indicating that you need a mast head antenna to have a successful class B installation.

[a64pilot]

Originally Posted by MarkJ

I thought you would have read the myriad of AIS threads?

I can't find any Class B AIS thats available that has Bluetooth at all. One has it but wont work on iPad.

I dont think any iPad aps use Bluetooth... I have iNavx, Garmin and Navamatics and none use AIS as far as I can see.


Mark

I have, but there are so many and to someone without prior knowledge they are a little overwhelming, there is such a thing as too much info.
As far as AIS, I'm a pig looking at a wrist watch
Wifi is fine, I had assumed Bluetooth, but Wifi is probably better

[jannw]

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

[colemj]

Originally Posted by Paul L

The Class B are designed for short distance, both to reduce cost and congestion. Seems reasonable to use the device as it was designed.

I don't understand that logic. Are you suggesting that Class B is designed for surface-level mounting only and that putting it any higher is outside its design specs (and a societally bad thing to do)? Why not put it below decks where it would have even shorter range and one could feel even better about oneself in not being a "congester"? Or get a receive-only unit?

I think the design spec for Class B took range into account using power and transmission interval - not antenna height. I don't think anyone views having a class-B antenna 50-60' above water is a bad thing - technically or socially.

40nm is an extreme range for sure, but how about 20nm? 10nm? More important is the transmission range - the people I have talked with that removed their stern mount for a masthead mount were claiming 3-4nm max transmission that improved to 8-10nm. That is significant to me.

However, like you, I don't have any problem with the antenna mounted anywhere. I was just pointing out some of the trade-offs (and implying which way we went in deciding).

Mark

[Dockhead]

A few comments, just my opinions:

1. First of all, you will find that adding an AIS transponder to be one of the best things you ever did to your boat, at least, if you sail anywhere where there are ships about. You will be amazed how you ever lived without it (I do almost every day).

2. Second, I would not make a fetish of its being stand-alone. A black box unit which integrates with your regular nav system works really well, is cheaper, takes up no space at the helm, etc. If your regular nav system goes down, lack of AIS will not be your biggest problem. AIS targets overlaid on plotter and radar screens are vastly more useful than just displayed in a vacuum. But all that being said, if you have space for a separate display, and still want one after considering all these arguments, the Vesper units are highly praised everywhere, and have some advantages in the way they display data compared to other devices (like relative positions at CPA).

3. There are many advantages to a separate antenna for AIS, especially, you are doing nothing to compromise your regular VHF antenna, which is a critical safety device. Remember a splitter not only degrades the regular VHF signal, it also introduces two more connectors and another device, which are all points of potential failure. A separate AIS antenna need not be at masthead height; mine is on the first (lowest) spreader and works great. I think it might even be ok on the pushpit. Splitters work ok, but if you can possibly manage the extra PITA for pulling cable for a separate antenna, you will be richly rewarded.

4. The more range the better. You may not need to know what your CPA is with a ship 40 miles away, but it is terrific being aware that early that he is there and moving generally in your direction. I get 40 or 50 miles out of my system, and sometimes much more, with the antenna at the lowest spreader -- height is not a big problem with ships since their antennae are high up. A bigger problem is poor cabling and installation of the antenna. If you take care to use really good coax (I use RG213) with a minimum number of maximum quality connectors, you will reap rich rewards in range and reliability of the AIS system. Just like with any radio, the whole system is only as good as the antenna and cabling, which are on the whole more important than the radio itself.

[a64pilot]

I think I'll go the splitter route to avoid congestion, another wire in my mast and all that work, mostly to avoid all that work

[Dockhead]

Originally Posted by colemj

I don't understand that logic. Are you suggesting that Class B is designed for surface-level mounting only and that putting it any higher is outside its design specs (and a societally bad thing to do)? Why not put it below decks where it would have even shorter range and one could feel even better about oneself in not being a "congester"? Or get a receive-only unit?

I think the design spec for Class B took range into account using power and transmission interval - not antenna height. I don't think anyone views having a class-B antenna 50-60' above water is a bad thing - technically or socially.

40nm is an extreme range for sure, but how about 20nm? 10nm? More important is the transmission range - the people I have talked with that removed their stern mount for a masthead mount were claiming 3-4nm max transmission that improved to 8-10nm. That is significant to me.

However, like you, I don't have any problem with the antenna mounted anywhere. I was just pointing out some of the trade-offs (and implying which way we went in deciding).

Mark

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.

For my setup: 40 or 50 miles receive is minimum. Right this minute 5 miles inland up the Hamble River on my mooring, and behind the whole Isle of Wight, I can see ships in the Channel more than 30 miles away, and that is typical. This proves, by the way, that VHF is not strictly line of sight, as the IOW has rather high hills in the middle of it which block my line of sight to the Channel.

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

Height is modest -- 10 meters above the water on my lowest spreader. But it's a high quality Diamond antenna with high quality cabling -- a straight run of RG213 all the way to the nav table with only two connectors (I did not put in disconnect connectors at the mast base; the cable will have to be cut or pulled out from behind the nav table the next time I pull the mast).

The antenna and cabling play a huge role in system performance.

[colemj]

Originally Posted by Dockhead

3. There are many advantages to a separate antenna for AIS, especially, you are doing nothing to compromise your regular VHF antenna, which is a critical safety device. Remember a splitter not only degrades the regular VHF signal, it also introduces two more connectors and another device, which are all points of potential failure. A separate AIS antenna need not be at masthead height; mine is on the first (lowest) spreader and works great. I think it might even be ok on the pushpit. Splitters work ok, but if you can possibly manage the extra PITA for pulling cable for a separate antenna, you will be richly rewarded.

The good splitters (Vesper and Navico, for example) have <1dB TX insertion loss, and a 12dB RX GAIN. So there is no TX penalty for a splitter, while there can be a RX advantage.

All good splitters are left in VHF mode when powered down or failed. There is no way they can fail and leave your VHF disconnected (well, I suppose a lightning strike or fire could disintegrate them completely).

You will not be richly rewarded using a separate antenna - particularly if you mount them on the pushpit. As I mentioned earlier, you get a 12dB GAIN in RX using a splitter, and the TX insertion loss is almost immeasurable.

Your point about quality cabling and connectors is most important (we have 1/2" Heliax to the antenna and LMR400 pigtails connecting the splitter!).

I think all the negativity regarding splitters is due to the quality and performance of all the past generations of them - some were truly horrendous.

However, the new ones are not the same - they have specs that can exceed separate antennas in RX with no TX insertion losses. Coupled with the antenna mounted higher up, performance will be much better with a good splitter than with a separate antenna on the pushpit.

Mark