AIS Antenna on Spreaders

[redsky49]

Has anyone any experience with such an installation? Decent reception? Any interference with halyards or other lines? Maybe mount Wi-Fi antenna on opposite spreader?

How did you mount it and how was the cable routed?

Top of the mast is already too busy and I am too old to climb all the way up if the spreaders will do.

And will RG-8X be adequate for the antenna cable?

TIA

[laika]

This maybe isn't what you're looking for, but I installed a vesper splitter about 6 months ago and it works great. Solves the placement dilemma and hassle you mention. Failure would not inhibit VHF comms and, similarly, when turned off the VHF is still operable (thus can be fused and wired directly to the AIS breaker). Consumes negligible electrons.

Simple, works well, easy peasy. I carry a backup antenna, but mine is mounted above a cockpit radar tower so relatively easy access.

[model 10]

Not to be too funny, but are you kidding? Unless you have invented an ais antenna that is about 3" high, not 3' that would not work.

[yttrill]

I have a dedicated AIS antenna on my top spreader connected to a Garmin AIS600 transponder, as well as a Garmin VHF300AIS radio, which has AIS receive capability built in, connected to the mast top VHF antenna. Both AIS receivers can feed my plotter via NMEA2000 bus. The transponder has a dedicated GPS. The AIS output from the radio is normally disabled to avoid confusing the plotter with two signals.

The AIS600 contains a splitter which I use to connect my backup VHF radio to the AIS antenna. Both radios and both AIS systems work well when operating.

[yajie boy]

Originally Posted by yttrill

I have a dedicated AIS antenna on my top spreader connected to a Garmin AIS600 transponder, as well as a Garmin VHF300AIS radio, which has AIS receive capability built in, connected to the mast top VHF antenna. Both AIS receivers can feed my plotter via NMEA2000 bus. The transponder has a dedicated GPS. The AIS output from the radio is normally disabled to avoid confusing the plotter with two signals.

The AIS600 contains a splitter which I use to connect my backup VHF radio to the AIS antenna. Both radios and both AIS systems work well when operating.

be careful I am now using my fourth Garmin AIS 600 the thing was telling me I was the dangerous vessel crashing into myself. Garmin Service was not acceptable.

[Wanderlust]

Don't listen to Guy. I too have my AIS antenna mounted on the spreader and it works fine.

It's the Shakespeare 5215AIS which is a bit under a metre tall. I made a bracket from stainless plate and had my rigger rivet that to the spreader half way between mast and spreader tip. The bracket positions the antenna almost level with the front of the mast and the forward diamond protects it from the genoa.

I know you didn't ask about splitters or separate antennas, but no doubt you will get more suggestions to go the splitter route. I put a lot of thought into whether it was better to have a splitter or a separate antenna. As with everything on a boat, there are compromises. The separate antenna worked out a little dearer after buying cable and the time for the rigger to fit it, but the difference was not significant. So for me it was a close decision, but came down to usage in practice.

The splitter argument
With a splitter, you would be using the best located antenna (masthead for me), so more range. But long range in AIS is not important for me so I discounted this benefit. As it turns out, I have tried swapping antennas and the difference in reception is marginal. Most splitters reduce the signal a little so it would be worthwhile to find one that minimises this (e.g. Vesper).

What I saw as a downside for the splitter solution was the fact that AIS communication is disconnected while you are on the radio. So if you happen to be on the radio when your AIS transmits, the signal will not go out, and you will also not receive incoming signals. You will not know this has happened.

There could be rare occasions when the AIS is effectively dumb and blind. Maybe you are on the VHF trying to raise the very vessel you want to see or be seen by on AIS.

The separate antenna argument
In this case you have redundcancy and abiliity to easily swap cables. The downside is you will not know if the mast shadow is interfering with transmission or reception. I haven't seen any evidence of this happening but it must affect the signal if the antenna is hidden by the mast. There is a small angle abeam where signal could be affected. As you get closer, with stronger signal strength this effect should reduce. Mounting on the starbord spreader could be a slight advantage.

So each solution has benefits and disadvantages.

Back to your question ..... yes a spreader mounted AIS antenna works fine.

[colemj]

Originally Posted by Wanderlust

Most splitters reduce the signal a little so it would be worthwhile to find one that minimises this (e.g. Vesper).

What I saw as a downside for the splitter solution was the fact that AIS communication is disconnected while you are on the radio. So if you happen to be on the radio when your AIS transmits, the signal will not go out, and you will also not receive incoming signals.

The Vesper splitter actually amplifies the received signal, so signal reception is better when passed through the splitter compared to not.

Class A transmission rates are every 2 or 6 seconds (speed and ROT dependent). Unless one is sitting on the mic key keeping the VHF side of a splitter open, it is unlikely that missing 2 seconds of data update every once in a while will be meaningful. If it becomes meaningful, you have made a navigational error beyond any fault of an AIS splitter.

Class B transmissions are every 30 seconds, so having an open VHF mic will have a greater probability of longer time intervals between updates. However, most class B transponders are used in vessels that are moving at relatively slow speeds and are more maneuverable, so even missing a minute or two of updates here is insignificant in practice.

Mark

[model 10]

I guess with the kind of sailing or motoring ole wanderlust does a loose halyard or sail never get near the spreader. Sure.

[Wanderlust]

Re Colemj's comment on splitters ..

Originally Posted by colemj

..... so even missing a minute or two of updates here is insignificant in practice.

Mark

Yep I mostly agree. I just saw a slight possibility that several Class B transmissions in/out could be lost. Maybe you or the other vessel (or both) changed course due to close proximity at night and you are trying to verify what you see or warn them by repeatedly calling them on VHF, thus preventing the AIS transmissions in either direction on those times. The chances of missing several in a row are remote, but people do win lotteries.

Anyway, I don't have a strong argument for or against either solution because they are each a compromise. For me it was a close decision and you won't find me arguing against splitters. They are an equally good solution.

[transmitterdan]

Mounting the antenna on a spreader will not cause any problem with the AIS functioning. If you are worried about a halyard catching on the antenna consider mounting the antenna to the underside of the spreader. Radio signals can't tell if the antenna is upside down.

[Paul Elliott]

My AIS antenna is on the top spreader, and the coax is routed down through the mast. I've had zero problems with halyards, or spinnaker rigging, and since the antenna is flexible I don't see how a halyard could really get seriously hung up.

But, when flying the spinnaker in extremely light wind the sailcloth has brushed against the antenna tip. This could rip the spinnaker. I'm considering running a light nylon line from the antenna tip up to the shroud above, which would keep this from happening.

The spreader-mount antenna definitely gets more range than my previous stern-rail mounted antenna. I don't think there are any significant mast "shading" issues, but I haven't done a careful pattern check.

[yttrill]

If you have a reasonably modern plotter you do not need an "AIS display", just plug the AIS digital output into your plotter. If you're using a slow NMEA 183 connection method turn off the AIS in Sydney Harbour (or everything else will be killed by the flood of AIS traffic).

If you have an old plotter .. consider replacing it instead of an "AIS display". If you can make it, have a look at the Sydney Boat Show starting July 30. My plotter is a touchscreen which overlays the AIS onto the chart. you can just touch a vessel and get all the data. It also show the CPA (Closes Point of Approach) visually and numerically, which is what you need to know to avoid a collision.

An essential device for travel up the East Coast of Oz because one is usually in the middle of a shipping lane. This is also the second safest place to sail, the safest being 50+ miles offshore. The evil enemy out there is the fishing boat. They don't show on AIS and they don't show on radar and they're short handed (no skipper on bridge) and night blind. But they tend to avoid bulkies too.

[The Garbone]

I have an AIS antenna on my spreader. We had just restepped the mast a few weeks ago and I went out this weekend to find my mast top vhf whip had been vaporized by a lightening strike. Lucky for us I have not yet installed our new VHF radio so that was spared but now the spreader antenna is our primary until I can get around to climbing the mast.

Interesting is that the strike fried all the LEDs and indicators on the starboard side of the boat and our solar charge controller. Oh well....

[a64pilot]

On locating the display, my Vesper Watchmate is down below, I have not yet connected it my plotter and can attest that having it down below is not a good solution, yes you do still hear the alarm, but you have to go down below to see what and where and to silence the alarm, and the alarm can get annoying as you may get several for the same target.
But I think that having it down below, but connected to the plotter is best, I'm trying to keep the helm as uncluttered as possible

[colemj]

If you have a wifi AIS unit, or a wifi NMEA bridge, then using a tablet to view the AIS data in the cockpit (or anywhere else) is a great solution. In general, many of the tablet apps are far superior to chartplotters when it comes to presenting and using AIS data.

Mark