AIS- A Love Story

[jt_kilroy]

Correct, the units I have tested are very directional, very little reception from behind, maybe 2 miles vs. 50 miles. Like was pointed out, not practical for a boat.

[Cadence]

Originally Posted by jt_kilroy

Correct, the units I have tested are very directional, very little reception from behind, maybe 2 miles vs. 50 miles. Like was pointed out, not practical for a boat.

Yep, seems like an omnidirectional antenna makes more sense.

[Jon Eisberg]

Originally Posted by Don C L

Where I am, where fog can roll in while you are crossing a shipping lane, and an AIS blip will not be mistaken for anything else... I am saving up for the full enchilada. But even now I can see others on my cell phone as long as I am in range of a tower. Pretty amazing stuff for old guys who grew up with ded. reckoning, Loran, RDF etc.

AIS from a cell phone ???

Are you referring to accessing a web-based source of AIS info such as MarineTraffic.com? If so, that's not a very good idea... ;-)

From their FAQ page, emphasis mine:

Can the web-published information be used to enhance safety at sea?

This is not the intention of this system. Data provided can only be used by Internet users for informational reasons only and they are by no means related to safety of navigation. Information provided may be incomplete, obsolete or contain errors and cannot substitute the on-board safety equipment and of course the good seamanship.

Comparing the display from marinetraffic with an onboard AIS can often reveal some startling discrepancies. While some of the information MIGHT be better than nothing, it could just as easily be WORSE than nothing ;-) No way should such web-based reporting be relied upon for collision avoidance in limited visibility...

[laika]

Originally Posted by TJ D

By the way, we are using the Vesper automatic splitter. I think it cost about $200, so one could run another antenna if desired for less, but I just didn't feel like it!

I don't think that manual ones are a good idea if one's going to use a single antenna, since you would only have functionality on one thing or the other, and we do like to keep a listening watch on the VHF all the time.

TJ

I've purchased the Vesper splitter a few months ago for $249.

It uses almost no power and does not need to be turned on for VHF to operate (thus can be fused and wired to the main AIS breaker). Likewise, if it fails, VHF will still operate.

[Exile]

Originally Posted by laika

I've purchased the Vesper splitter a few months ago for $249.

It uses almost no power and does not need to be turned on for VHF to operate (thus can be fused and wired to the main AIS breaker). Likewise, if it fails, VHF will still operate.

That's really good to know. Should one desire a separate antenna for AIS, however, I noticed that the Vesper website shows a couple of AIS-specific ones that operate on a more desirable frequency, apparently. Which brings to mind the next question for those of us, like me, who may be not all that technologically savvy:

Can the AIS antenna be mounted alongside the Vhf antenna at the masthead, or is it better to mount it, for example, on a spreader perhaps. Not sure if there might be interference if they were too close together.

Thanks.

[colemj]

Frankly, I think the "AIS" antennas are just a way to separate people from their money. Yes, they are tuned for the AIS frequency, but it makes no practical difference in performance. I have used a VSRW meter on 5 different common VHF antennas fed by AIS and every one of them had a 1:1 SWR (same system with the antenna the only variable).

Mark

[laika]

Originally Posted by colemj

Frankly, I think the "AIS" antennas are just a way to separate people from their money. Yes, they are tuned for the AIS frequency, but it makes no practical difference in performance. I have used a VSRW meter on 5 different common VHF antennas fed by AIS and every one of them had a 1:1 SWR (same system with the antenna the only variable).

Mark

Another option, I know Vesper and probably some others offer antennas that are tuned in between the AIS and VHF frequencies. OTOH, I'd personally be more inclined to sacrifice a slight bit of AIS range to maximize VHF.

[Exile]

Originally Posted by colemj

Frankly, I think the "AIS" antennas are just a way to separate people from their money. Yes, they are tuned for the AIS frequency, but it makes no practical difference in performance. I have used a VSRW meter on 5 different common VHF antennas fed by AIS and every one of them had a 1:1 SWR (same system with the antenna the only variable).

Mark

At least as far as an AIS receiver goes, your observations & opinion are certainly consistent with the performance of my Metz antenna connected to a VHF & AIS receiver w/splitter. I seem to have excellent range, clarity & consistency with both systems through this set-up. It sounds like there's little downside to also going with a splitter for an AIS transponder.

[colemj]

Receive is fairly immune to bad antenna performance - it is transmitting where you get bit.

I think a Vesper or Simrad splitter will out-perform a separate antenna mounted on the mast head next to the VHF antenna or on a back rail or on a spreader. My opinion is that the only reason to go with a separate antenna is redundancy.

Many other splitters have large losses and should be avoided. There may be other good ones than the two I noted, but any splitter should have <1db insertion loss. If they do not publish that spec, then don't buy.

Mark

[Exile]

Originally Posted by colemj

Receive is fairly immune to bad antenna performance - it is transmitting where you get bit.

I think a Vesper or Simrad splitter will out-perform a separate antenna mounted on the mast head next to the VHF antenna or on a back rail or on a spreader. My opinion is that the only reason to go with a separate antenna is redundancy.

Many other splitters have large losses and should be avoided. There may be other good ones than the two I noted, but any splitter should have <1db insertion loss. If they do not publish that spec, then don't buy.

Mark

Informative & most helpful . . . as usual Mark!

For redundancy, I've already installed a spare antenna on my aft rail. Seemed a whole lot easier than installing another one anywhere up on the mast, and would certainly be adequate to get me home.

[lordgeoff]

Originally Posted by TJ D

My love story begins like so many others, on a stormy winter night in the Bering sea.

Back about 2006 or so, we were mandated to install class A systems on our trawler. It really just seemed like another case of government overreach, creating yet another requirement on top of an already endless list. However, we had no choice so we complied.

Now, for as long as there's been a fishing fleet working out of Dutch Harbor, we've had to cross one of the main shipping lanes between the west coast and Asian ports. These guys operating these ships more often than not would disregard the rules and simply continue on their course regardless of the crossing situation. All very annoying, but we learned to live with it. For you colregs enthusiasts, there are no TSS areas where we're talking, no special exemptions. Calls by position, course, speed, whatever would almost always go unanswered. It's just the way it was.

Until the night I was crossing the lanes with our shiny new AIS. Suddenly, I had identifying info for everyone! We could call these guys by name, and they knew we knew who they were. And just like that, the vast majority of them would take appropriate action in a crossing/meeting/overtaking situation without so much as a radio call. Amazing! I immediately bought a receiver for the sailboat, followed by a class b transponder when they were available.

For those still reading, here's the point. This is the single most important contribution to maritime safety since the advent of electronic positioning. We also embrace the KISS principal on board (the sailboat, not the trawler), but this system has a place on any boat venturing out in any area where shipping traffic is present, coastal or offshore. I read about and remember well the difficulties posed by commercial traffic in various ports, and these units just take so much of that away.

I don't know what compelled me to write this today. It probably has something to do with Shell's new arctic oil rig pulling into Dutch last night with 5 attending tugs and so many damn lights that I appreciated the technology anew.

Good sailing to all.

TJ

....can anyone advice how I can integrate the AIS Real time info with my paper charts and sextant navigation?

[Jon Eisberg]

Originally Posted by lordgeoff

....can anyone advice how I can integrate the AIS Real time info with my paper charts and sextant navigation?

This should help you get started...

;-)

https://www.youtube.com/watch?v=9Qov01O1mg8

[lordgeoff]

Originally Posted by Jon Eisberg

This should help you get started...

;-)

....maybe time to file the the paper charts and sextant in a warm dry locker and get a GPS and Chart Plotter?.

[colemj]

Originally Posted by lordgeoff

....maybe time to file the the paper charts and sextant in a warm dry locker and get a GPS and Chart Plotter?.

No need - they make AIS models with their own standalone display. Although the very act of bringing an AIS onboard will also bring its GPS along for the ride.

Mark

[MYTraveler]

Originally Posted by jt_kilroy

Has anyone that is not commercially required sprung for a class A 12.5W device vs. the class B 2W?

I would be very interested to hear from users about the ranges at which they are able to see vessels vs. their antenna heights. On inland waterways, where most of my work is centered. With antenna heights coming close to 70 ft off the water I have seen as far as 80 miles.

I have class A (Furuno FA-150). The base of its antenna is about 35'. Range offshore routinely exceeds 100nm, with a picture to demonstrate: