AIS Antenna on Spreaders

[jeffrobbins]

For what it's worth... I don't recommend putting AIS antennas on the spreaders unless the boat is quite large. That's because to get the best performance VHF antennas need horizontal separation from other antennas and reflective objects. 4' of free space is the NMEA recommendation. It won't generally affect your receive range but transmit performance will be affected. And as you move the antenna away from the mast, a typical 1/2 wave whip at around 3' long might put the tip quite close to the rigging.

[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

[alphabravo2]

I have a Broadblue 385 Catamaran and have installed the AIS antenna on my lower spreader, wire going through the mast with a short run on the spreader. I did the install 3 years ago, no issues. Reception is excellent in all conditions. I send and receive a signal from -to boats 18-20 miles away. My AIS Unit is a Raymarine 650 I think. The top of my mast was also too busy. The lower spreader has to be 25 feet up in the air... Plenty high!

[Rapanui]

I would (and have on my previous boat) put a dedicated AIS aerial on the pushpit, for 2 reasons:
* The reception there will be about 20 miles given the aerial heights of nearly all transmitting vessels. To me, thats more than enough given the traffic density in the English Channel. What sensible action can you take at long range given the inaccuracies inherent in calculating CPA at such distance?
* It gives you an emergency VHF aerial if your stick falls down which you know works.
Its also a lot easier to install
Stephen

[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.

[Dockhead]

Originally Posted by Guy

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

I have three antennae on my first spreader, including a 5' ham radio VHF/UHF antenna. Never a problem in thousands of miles including three North Sea crossings. This position is protected by the intermediate shroud on a multi-spreader rig (mine has three spreaders). You shouldn't extrapolate the way your boat works, to cover all boats. On many boats, spreader-mounted antennae (and radar domes, and other stuff) work just fine.

[redsky49]

It seems that a successful installation can be achieved with the antenna mounted in various locations. That is good to know. I am leaning toward the use of a splitter or mounting on the pushpit. If stern rail is the ultimate choice, I might install a post with arms for multiple antennas (my antenna farm) as the rail is starting to be rather congested.

I am also starting to consider WiFi/tablet, etc, in addition (or alternative) to a dedicated device such as the Vesper Watchmate 8500 which has previously been my objective.

Appreciate all the various options/opinions!

[Paul L]

I asked this question to two antenna manufacturers:

This is not recommended as it will have adverse effects on the radiation pattern of the antenna and throw it 180 degrees out of phase for what you are trying to receive.

The other said:

I think your setup will be okay with a minimum of 3ft away from the mast. The more the better.

This was to a question about mounting the antenna on a spreader pointing down.

[transmitterdan]

Originally Posted by Paul L

I asked this question to two antenna manufacturers:

The other said:

This was to a question about mounting the antenna on a spreader pointing down.

That first one is a doozy. Don't buy antennas from stupid companies.

[savoir]

If you are concerned about something catching on the antenna then mount it further outboard. Support the antenna by tying it to the diagonal. The diagonal will have to be sleeved with some plastic tube.

[svlamorocha]

Originally Posted by Paul L

I asked this question to two antenna manufacturers:

The other said:

This was to a question about mounting the antenna on a spreader pointing down.

What manufacturer said that "..it 180 degrees out of phase for what you are trying to receive"? That sounds like rubbish to me.

There may be an impact though. If the antenna is design to maximize gain at a "downangle" (a bit below horizontal) then the angle will be inverted. That said, I would expect an antenna designed for a boat (as opposed to an antenna designed for a mountaintop repeater or shore station) to have max gain at exactly horizontal, in which case it would not matter if you inverted it.

[Paul L]

Originally Posted by transmitterdan

That first one is a doozy. Don't buy antennas from stupid companies.

The first one was Shakespeare, the second Digital Antenna.