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Old 21-06-2013, 07:54   #16
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Re: considering an ais transponder, any recommendations?

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Originally Posted by jeremiason View Post
When I originally commissioned this boat I had a Nobletech AIS receiver installed, which required its own AIS antenna on the stern rail and displayed on my Raymarine Chartplotter.

Just before we started cruising, I purchased a Raymarine AIS 500 Class B unit, which had a built in VHF Antenna Splitter. The unit has a built in sensor that allows the VHF to override the AIS unit.

Since I now had two antennas on my boat, I switched back and forth to see how much the difference in height mattered to the VHF signal.

The masthead is about 65 feet off the water and my transmitted signal traveled about 10-12 miles. And reception was over 60 miles.

On the stern antenna, which is about 15 feet off the water, transmitted about 6 miles and received about 20-25 miles.

IMHO, if you are installing a Class B AIS Unit, you want the VHF antenna as high as possible. Not so much for reception, but for transmitting as far as you can allowing other vessel to see you sooner.

The mast falling theory always comes up, but again IMHO, you have much more of a chance of being run over by another boat/ship than you do of having your mast fall down.

Of course in my case I ended up installing a second VHF radio on the boat and connected it to the stern rail antenna, just in case....
If your VHF signal can only be heard 12 miles out from an antenna 65 feet above the water, then I think you have antenna, or more likely, cable/connector problems. Even with my old antenna, I was getting excellent signal reports from 60 miles away, provided the other antenna was high enough (Solent Coast Guard from Cherbourg). Talk to ships 30 to 40 miles away. I presume you have a normal, 25 watt transceiver?

To the OP: the other reason not to use a splitter is signal losses. You've got not only the losses in the splitter itself, but in two additional sets of PL159/SO139 connectors. Plus you have all the risks of bad connections additional connectors and devices introduce.

In my opinion, it's much better to use a separate antenna, which is what I do, although I admit that it's a PITA. My AIS antenna is on the first spreader, which is high enough (10 meters) for that purpose.
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Old 21-06-2013, 08:02   #17
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Re: considering an ais transponder, any recommendations?

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If your VHF signal can only be heard 12 miles out from an antenna 65 feet above the water, then I think you have antenna, or more likely, cable/connector problems. Even with my old antenna, I was getting excellent signal reports from 60 miles away, provided the other antenna was high enough (Solent Coast Guard from Cherbourg). Talk to ships 30 to 40 miles away. I presume you have a normal, 25 watt transceiver?
I read his range(s) to mean the AIS transceiver, not the comms radio.
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Old 21-06-2013, 08:05   #18
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Re: considering an ais transponder, any recommendations?

I think he meant VHF:

"Since I now had two antennas on my boat, I switched back and forth to see how much the difference in height mattered to the VHF signal.

The masthead is about 65 feet off the water and my transmitted signal traveled about 10-12 miles. And reception was over 60 miles"

But I guess he can speak for himself.
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Old 21-06-2013, 08:19   #19
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Re: considering an ais transponder, any recommendations?

AIS is technically a VHF signal. It even uses two of the marine-band VHF channels.

I also assumed that jerimiahson was describing his 3-Watt Class-B AIS transmit range. But this is ambiguous. And even an A/B test of VHF range will be questionable, since there are so many other uncontrolled variables.

For what it's worth, when I moved my AIS antenna from the stern rail to the upper spreader the receive and transmit range improved significantly. I haven't tried a splitter. I have an ACR "Nauticast" Class-B transponder and am completely happy with it. Since I installed that there have been many other transponder models introduced, so I don't know what I would install if I were starting fresh.
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Old 21-06-2013, 09:23   #20
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Re: considering an ais transponder, any recommendations?

There are three important issues with buying a class B AIS that are not immediately apparent from the brochures and perhaps they are relevant to some.

1. The cheaper splitters don't let you transmit VHF with the AIS on. To get that feature you have to buy one of the more expensive ones such as the Si-Tex which is currently around US250. On the other hand you might have a second VHF available.
2. Most of the units cannot properly network with a NMEA2000 system. The only one I know of that can is the Raymarine AIS650. The others force you to feed data into the AIS from its own GPS antenna. They cannot communicate with your network antenna so you must thread yet another wire and drill yet another hole. The only possible communication with the network is data out.
3. The ones that brag about a built in GPS antenna are really offering nothing. To benefit from that feature you will have to mount the unit in the cockpit or at least beside a hatch. Unlikely for most.
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Old 21-06-2013, 09:24   #21
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Re: considering an ais transponder, any recommendations?

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For what it's worth, when I moved my AIS antenna from the stern rail to the upper spreader the receive and transmit range improved significantly.
This brings up the question of what range is optimal for AIS?????

The AIS system is a tool to be used for collision avoidance. In that context, one needs to determine the useful range for the information it delivers. Factors include the speed of your vessel vs. the expected speed of other vessels.

For my average vessel speed of 6.5-7kts, I considered a transmit range of 5nm and receive range of 5nm for Class B and 10+nm receive range for Class A to cover 99+% of the any vessel traffic I'll ever care about. That coupled with the ease of stern rail mounting is the reason mine is that way.

The issue with range and AIS is not the same as VHF comms where more range is better. You only need what is necessary, anymore simply adds useless traffic/garbage to the system (yours and others).

The exuberance exhibited by some to know the data on a vessel out-of-range of becoming a CPA threat simply doesn't make sense to me.
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Old 21-06-2013, 10:10   #22
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Re: considering an ais transponder, any recommendations?

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Originally Posted by DotDun View Post
This brings up the question of what range is optimal for AIS?????

The AIS system is a tool to be used for collision avoidance. In that context, one needs to determine the useful range for the information it delivers. Factors include the speed of your vessel vs. the expected speed of other vessels.

For my average vessel speed of 6.5-7kts, I considered a transmit range of 5nm and receive range of 5nm for Class B and 10+nm receive range for Class A to cover 99+% of the any vessel traffic I'll ever care about. That coupled with the ease of stern rail mounting is the reason mine is that way.

The issue with range and AIS is not the same as VHF comms where more range is better. You only need what is necessary, anymore simply adds useless traffic/garbage to the system (yours and others).

The exuberance exhibited by some to know the data on a vessel out-of-range of becoming a CPA threat simply doesn't make sense to me.
For me the longer is the better. Average vessel speed being whatever it is, if I'm underway at night (or my wife is up) and there's a possible collision that's going to occur in 30-40 minutes, getting started on possible sail changes can easily eat into that time.

I don't need to set T/CPA alarm for 20 miles out, but it doesn't mean there's any harm in flipping through the contacts and seeing what's going on out there. Why you would purposefully choose to reduce the amount of information you have access to doesn't make any sense to me; you can just drop the range on the receiver itself to filter out distant contacts.

But factoring in a ~20 minute watch check to see a contact and ~10 minutes to prepare preventers and execute a gybe properly, nevermind re-adjusting trim and steering gear. To me that means I want to know everything out there as early on as I can.
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Old 21-06-2013, 10:17   #23
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Re: considering an ais transponder, any recommendations?

Quote:
The issue with range and AIS is not the same as VHF comms where more range is better. You only need what is necessary, anymore simply adds useless traffic/garbage to the system (yours and others).

The exuberance exhibited by some to know the data on a vessel out-of-range of becoming a CPA threat simply doesn't make sense to me.
The Op was talking about a transceiver, range is always good in that case.

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Old 21-06-2013, 10:23   #24
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Re: considering an ais transponder, any recommendations?

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Originally Posted by savoir View Post
There are three important issues with buying a class B AIS that are not immediately apparent from the brochures and perhaps they are relevant to some.

1. The cheaper splitters don't let you transmit VHF with the AIS on. To get that feature you have to buy one of the more expensive ones such as the Si-Tex which is currently around US250. On the other hand you might have a second VHF available.
2. Most of the units cannot properly network with a NMEA2000 system. The only one I know of that can is the Raymarine AIS650. The others force you to feed data into the AIS from its own GPS antenna. They cannot communicate with your network antenna so you must thread yet another wire and drill yet another hole. The only possible communication with the network is data out.
3. The ones that brag about a built in GPS antenna are really offering nothing. To benefit from that feature you will have to mount the unit in the cockpit or at least beside a hatch. Unlikely for most.

which cheap splitters do you mean, all the ones Ive seen are around the 200 mark and are designed for AIS.

AIS and N2k, This is a moving dot, because since NMEA have belatedly released the PGN for static data, most AIS system are being updated, so you rcomments dont hold true in general anymore. for example SIMRAD is now N2K compatible.

Also note that Raymarine is only compatible with C/E wide series only and requires the latest software.

as for units with integrated GPS and antenns, like the Vesper 850, they will work in the cabin with only the fibreglass cabin top in the way


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Old 21-06-2013, 10:39   #25
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Re: considering an ais transponder, any recommendations?

Quote:
Originally Posted by savoir View Post
There are three important issues with buying a class B AIS that are not immediately apparent from the brochures and perhaps they are relevant to some.

1. The cheaper splitters don't let you transmit VHF with the AIS on. To get that feature you have to buy one of the more expensive ones such as the Si-Tex which is currently around US250. On the other hand you might have a second VHF available.
2. Most of the units cannot properly network with a NMEA2000 system. The only one I know of that can is the Raymarine AIS650. The others force you to feed data into the AIS from its own GPS antenna. They cannot communicate with your network antenna so you must thread yet another wire and drill yet another hole. The only possible communication with the network is data out.
3. The ones that brag about a built in GPS antenna are really offering nothing. To benefit from that feature you will have to mount the unit in the cockpit or at least beside a hatch. Unlikely for most.
I have a Sitek black box transceiver. It works perfectly on NMEA2000 with my B&G Zeus plotters.

Its built in GPS receiver works brilliantly from behind my nav table instrument panel. In fact, I've been using its GPS data on the N2K network as the primary position data since my main GPS has been stuck in Jersey customs.
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Old 21-06-2013, 10:46   #26
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Re: considering an ais transponder, any recommendations?

Because I have two VHF antennas I can decide which to use for a given circumstance.

Mast head and Rail Mounted.

Both come into my nav station. At sea I have the AIS on the mast head and VHF on the rail mount so I can TX/RX AIS the furtherest range.

But now I am in an anchorage for a few months I switch so the VHF has the Madt head antenna and the AIS is on the rail mount.

Its felxability and I like it
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Old 21-06-2013, 10:47   #27
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Re: considering an ais transponder, any recommendations?

I agree about maximum range needed, really a ship doing 30 knots on a reciprocal course to your own vessel doing 7 knots, if your range is only 10 miles you have just 17 minutes from when you see it. OK that's not likely to happen but..
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Old 21-06-2013, 10:47   #28
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Re: considering an ais transponder, any recommendations?

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For me the longer is the better. Average vessel speed being whatever it is, if I'm underway at night (or my wife is up) and there's a possible collision that's going to occur in 30-40 minutes, getting started on possible sail changes can easily eat into that time.

I don't need to set T/CPA alarm for 20 miles out, but it doesn't mean there's any harm in flipping through the contacts and seeing what's going on out there. Why you would purposefully choose to reduce the amount of information you have access to doesn't make any sense to me; you can just drop the range on the receiver itself to filter out distant contacts.

But factoring in a ~20 minute watch check to see a contact and ~10 minutes to prepare preventers and execute a gybe properly, nevermind re-adjusting trim and steering gear. To me that means I want to know everything out there as early on as I can.
I explained my usage of AIS. If you want something different, go for it. You can probably build a system to see Class A out 60nm and Class B out 15nm. I simply don't thinks that's necessary. I've been contacted by vessel name from 6nm by a tug towing a barge, a 30 minute TCPA, he was inquiring on my intentions. I believe on a larger Class A vessel with higher antenna, they can see me 6-9nm out. I can see them at 10-15nm, long before they see me. I don't see the cost benefit of extending that range.

We don't 'leave the helm' for 20 minutes at a time....5 minutes maybe. That coupled with dual MFDs we can watch from the salon or cockpit, depending on the purpose for leaving the helm.

I can't ever remember adjusting course more than 15 degrees for collision avoidance. And that was last minute as the approaching vessel changed his course 1/2nm away. Nothing as drastic as a gybe.

YMMV
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Old 21-06-2013, 10:50   #29
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Re: considering an ais transponder, any recommendations?

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The Op was talking about a transceiver, range is always good in that case.

dave
The question is how much?

The is a reason Class B is only 2 watts....if more range was required, it would be more powerful.
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Old 21-06-2013, 10:56   #30
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Re: considering an ais transponder, any recommendations?

yes but with a transceiver, its always good to try and get your class B signal to travel as far as possible. I mean if you have a fast cat at 40kts closing , wouldnt you want him to see you on HIS AIS as far away as possible.

SO why arbitrarily limit the range, The mast head antenna on most boats spends 99% of its time doing nothing, using a splitter and a high antenna maximises its use and the usability of an AIS transceiver.

Arguing about mast coming down is nonsense. Ive seen failing masts take out the whole radar arch electronics . Anyway you can make a VHF antenna by striping a piece of co-ax and a broom handle.

Those arguing that a day to day benefit shouldn't be utilised becuase a rare failure event will render it inoperable, I mean how do these people get in a car or an aircraft!!!.


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