While I'm at it asking questions, here is another one. I'm replacing my AIS receiver with a transceiver. It's the Raymarine AIS650 and doesn't have a built in splitter. Would you hook it up to the VHF antenna thats on the mast and ad a splitter or add a seperate AIS antenna? I got Davits with solar panels, thought about adding the AIS antenna and GPS antenna there.

The only drawback I can see with the antenna on the davits is the reduced range.

I have my AIS Antenna on my solar panels some 2 m off the water and have received signals from ships just over the horizon.

Can't see any point in trying to see vessels 50 nm away!

I would use the vhf antenna with a splitter. I had a seperate antenna Mounted on the Bimini on my previous boat which worked great until my spinnaker got caught on it and ripped a bloody great hole in a new spinnaker. The less things sticking out off a boat for things to catch on the better.

If you go with a splitter and get worried about the additional -3db loss of a passive splitter, a good backup is always an active splitter. Not really high gain, but they do..well, almost... cancel out any drop from the splitter, ie: -1db to 0db insertion loss. They don't draw much power either, the dc input is normally a 1 amp fuse.
An added bonus is they have a good and simple set of idiot lights that monitors the antenna interface to the ais transponder and vhf radio, which is handy for troubleshooting.
It's weird, they are technically a 'gain' device, but it kinda sounds wrong to call them an 'amplifier' when it is only zeroing out it's own loss .

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Jode5 said..
I would use the vhf antenna with a splitter. I had a seperate antenna Mounted on the Bimini on my previous boat which worked great until my spinnaker got caught on it and ripped a bloody great hole in a new spinnaker. The less things sticking out off a boat for things to catch on the better.

Yea I see that point but I have a cruiser with an arch, solar and a wind turbine that will go back on soon. I'll be adding a top-down furler for the asy, should reduce that risk as well as making it easier to manage the spinnaker.

Did you notice much difference in range between having the antenna on the back vs top of the mast?

With my AIS receiver, I get ships at about 13nm from the stick on the solar support (about 3m above water line) and about 23nm from the masthead (about 12m awl). Small craft much less as their antennae are lower.

VHF range from the lower stick is reassuringly good, but I use the masthead just to be sure. A second stick gives you redundancy. AIS range is reduced significantly by heavy wave motion and rain/fog.

Cheers, Graeme

I'd go with the separate antenna. I only use a small antenna racing style mounted on my radar pole about 4 or 5 m above the water and after testing against the full size antenna mounted at the top of the mast the difference in typical receiving range is around 18Nm vs 30Nm. I find this more than adequate and I've made it so both antenna leads terminate in a location such that the AIS and VHF can be quickly swapped over to either antenna (hence why i have been able to compare ranges). I like the idea of the redundancy and the reduced range (which is probably about the same as a sans mast powerboat would have) isn't an issue, IMHO.

If you think about AIS as an early warning indicator, with even a 13 nm range an errant container ship doing 20 knots and you doing say 6 knots head to head, that's still about 30 mins warning before you go bump.
Still pretty cool.

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shaggybaxter said..
If you think about AIS as an early warning indicator, with even a 13 nm range an errant container ship doing 20 knots and you doing say 6 knots head to head, that's still about 30 mins warning before you go bump.
Still pretty cool.

Yeah, I have my AIS to the davits & VHS to masthead - works well for me.

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jev7337 said..

Jode5 said..
I would use the vhf antenna with a splitter. I had a seperate antenna Mounted on the Bimini on my previous boat which worked great until my spinnaker got caught on it and ripped a bloody great hole in a new spinnaker. The less things sticking out off a boat for things to catch on the better.

Yea I see that point but I have a cruiser with an arch, solar and a wind turbine that will go back on soon. I'll be adding a top-down furler for the asy, should reduce that risk as well as making it easier to manage the spinnaker.

Did you notice much difference in range between having the antenna on the back vs top of the mast?

It really didn't make much difference for day to day sailing as you are usually not interested in anything more than a few miles away. Our antenna is 25m high and yes we do see boats a long way away but not all boats as it depends on how good their transmission is. If you are particularly looking for a boat that is a fair way away and you have phone rang, you will probably find them on MarineTraffic.

our AIS is connected by splitter to masthead vhf antenna. with this we routinely pickup ships at more than 50nm...up to 80nm on occasions.

this is great when deep sea, but even coastal - the further the better

i would definitely recommend this system

the only advantage in using a seperate antenna is if you lose the mast, you 'may' still have AIS (depend where the mast lands !). we get around this by having a spare emergency vhf antenna which we can rig on the targa bar

cheers,

Thanks all.
I think I'll add a splitter and get some more range, may come in handy for coastal and off-shore cruising.
An emergency VHF antenna sounds like a good idea too. Will probably pull a cable up to the davits and mount it there already, while I'm doing the GPS cable. Redundancy.

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PacificStar said..
our AIS is connected by splitter to masthead vhf antenna. with this we routinely pickup ships at more than 50nm...up to 80nm on occasions.

this is great when deep sea, but even coastal - the further the better

i would definitely recommend this system

the only advantage in using a seperate antenna is if you lose the mast, you 'may' still have AIS (depend where the mast lands !). we get around this by having a spare emergency vhf antenna which we can rig on the targa bar

cheers,

And to add to Pacstar's comments, if you do lose the mast you should have a smaller backup vhf antenna and cable pigtail in your spares locker anyway. I wouldn't think of going offshore without the obligatory impeller and winch pawl etc etc spare parts, a spare VHF antenna is no different.

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shaggybaxter said..

PacificStar said..
our AIS is connected by splitter to masthead vhf antenna. with this we routinely pickup ships at more than 50nm...up to 80nm on occasions.

this is great when deep sea, but even coastal - the further the better

i would definitely recommend this system

the only advantage in using a seperate antenna is if you lose the mast, you 'may' still have AIS (depend where the mast lands !). we get around this by having a spare emergency vhf antenna which we can rig on the targa bar

cheers,

And to add to Pacstar's comments, if you do lose the mast you should have a smaller backup vhf antenna and cable pigtail in your spares locker anyway. I wouldn't think of going offshore without the obligatory impeller and winch pawl etc etc spare parts, a spare VHF antenna is no different.

I thought I had a good amount of spares, engine maintenance, nav, comms, general repairs and tools etc. and still adding.
But I did not think about spare Winch Pawls.