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Old 24-12-2015, 18:21   #16
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Re: Vesper AIS SP-160 "relay/splitter" test results, lab/real world

FWIW,

1.Have yet to see a smaller yacht with a class A AIS. Occasional megayachts, yes, but they are really just fancy small ships!

2. We've had our Vesper splitter for a while now, and it has performed transparently. Routine reception of A class at ~40 miles, others report seeing us at 8-12 miles. However, just the other day the output on the "FM/AM" jack disappeared completely. Not mission critical,, of course, but I'll be getting on Jeff Robbins after the holidays.

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Old 24-12-2015, 19:31   #17
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Re: Vesper AIS SP-160 "relay/splitter" test results, lab/real world

Thanks Jim....other than the odd super yacht delivery, I have not used AIS on my own boat as in Asia, being low key was my preference.

But rules are changing so one must abide.

AIS talk about interference with GPS as well as other VHF antenna.

I will be putting on a new Mast head GPS for the new Furuno GP-33

Is it advisable to put them on separate Masts?
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Old 24-12-2015, 19:49   #18
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Re: Vesper AIS SP-160 "relay/splitter" test results, lab/real world

Quote:
Originally Posted by Pelagic View Post
Thanks Jim....other than the odd super yacht delivery, I have not used AIS on my own boat as in Asia, being low key was my preference.

But rules are changing so one must abide.

AIS talk about interference with GPS as well as other VHF antenna.

I will be putting on a new Mast head GPS for the new Furuno GP-33

Is it advisable to put them on separate Masts?
Others are likely more informed than I, but I don't think that interference betwen GPS and AIS is likely, for one is ~150 MHz and the other 2+GHz.

And conventional wisdom is that GPS antennas should be mounted not at the mast head but lower down where the motion of the sensor due to rolling is less. This reduces error in velocity and azimuth sensing. I don't know of any particular reason for mastheading it. But keeping the AIS antenna away from the other VHF antenna is correct, for they can indeed interfere with each other.

One of the radio gurus will likely step in with more detail...

Jim
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Old 24-12-2015, 21:25   #19
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Re: Vesper AIS SP-160 "relay/splitter" test results, lab/real world

On another thread where a guy lost his anchored sailboat in the Bahamas, while clearing in ......hopefully found now drifting about 45 nm away.. ...

someone mentioned AIS as a good precaution.

This got me thinking about how to wire up an AIS and its GPS so as to be a discrete tracker that could not easily be turned off by boat Thieves.

Has anyone done that?
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Old 24-12-2015, 21:37   #20
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Re: Vesper AIS SP-160 "relay/splitter" test results, lab/real world

Quote:
Originally Posted by Pelagic View Post
Thanks Jim....other than the odd super yacht delivery, I have not used AIS on my own boat as in Asia, being low key was my preference.

But rules are changing so one must abide.

AIS talk about interference with GPS as well as other VHF antenna.

I will be putting on a new Mast head GPS for the new Furuno GP-33

Is it advisable to put them on separate Masts?
I think there should not be any issue of interference between GPS antenna and AIS antenna. The physical size of each antenna is such that there would be high signal loss between them. Plus the frequencies are 5-6 octaves apart so that helps a lot.

But there is nothing to be gained in performance by putting the GPS antenna at the mast head and possibly some degradation depending on the height. Most GPS antennas are patch type antennas with their main lobe pointed up. They don't receive better when high above as opposed to a couple meters above the surface of the water (unlike VHF antennas which do benefit from greater height). The main criteria for antenna placement is a clear view of the sky. So if you have a handy place down lower to put the GPS antenna that would probably be preferred if for no other reason than maintenance. Also, some GPS antennas don't have very high gain and so long cable runs should be avoided.

A dedicated VHF AIS antenna ideally should be >1M from the marine VHF voice antenna. The distance can be either horizontally or vertically measured. They can be side by side >1M apart or directly above one another >1M apart.
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Old 24-12-2015, 21:51   #21
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Re: Vesper AIS SP-160 "relay/splitter" test results, lab/real world

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Understanding that w/splitter it is an either/or use of vhf/AIS....in real world use....how disruptive to critical AIS tracking would be the use of VHF in say a close quarter situation?
One of the main points of AIS is to eliminate a lot of talking on the VHF. You know where the class A ships are going (if they program their destination as required) so it should be easy to guess their next move.

Class A AIS units transmit information at between 2 and 10 second intervals depending on SOG and rate of turn. So generally speaking when you stop talking on the VHF you should have received updates from just about all class A targets in 10 seconds or less. So on that basis a splitter isn't a big deal.

Class B units only transmit every 30 seconds in the most common scenario. It is allowed that if a Class B "misses" its 30 second window it can make it up as soon as possible thereafter. I believe most class B units know the splitter is in voice transmit so they hold off. Then in the next available slot after voice stops they transmit their data. I have not tested units to see how well they handle this situation. I think all decent class B units would send an update within 90 seconds of voice transmit ending in the worst case and typically it should be 30 seconds or less.

I don't think it's a good idea to get a class A unit for a recreational boat. In crowded situations the big ships need to get updates from one another. Cluttering up the time slots with lots of recreational craft messages is not the neighborly thing to do IMO. Plus programming all the data for class A is a PITA.
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Old 25-12-2015, 06:54   #22
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Re: Vesper AIS SP-160 "relay/splitter" test results, lab/real world

Quote:
Originally Posted by Pelagic View Post

This got me thinking about how to wire up an AIS and its GPS so as to be a discrete tracker that could not easily be turned off by boat Thieves.

Has anyone done that?

All you would need to do is hide it somewhere not obvious and don't power it through a switch on your main panel labeled "AIS".

One of the black box types like the Vesper 8000 work best for this because there is no user interface/display attached to them.

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Old 25-12-2015, 07:03   #23
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Re: Vesper AIS SP-160 "relay/splitter" test results, lab/real world

We have seen/met several recreational cruising boats using class A -most of them of the <80' Nordhaven-types (not necessarily that brand, but I don't know how to classify them). I don't recall ever seeing a sailboat with one (one of the members here excepted, since his is an unusual arrangement). The mega yachts may be required by law to have them based on size and charter use.

Seems to me that the faster and more maneuverable a boat is, the more they should have class A.

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Old 25-12-2015, 07:39   #24
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Re: Vesper AIS SP-160 "relay/splitter" test results, lab/real world

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Originally Posted by colemj View Post
We have seen/met several recreational cruising boats using class A -most of them of the <80' Nordhaven-types (not necessarily that brand, but I don't know how to classify them). I don't recall ever seeing a sailboat with one (one of the members here excepted, since his is an unusual arrangement). The mega yachts may be required by law to have them based on size and charter use.

Seems to me that the faster and more maneuverable a boat is, the more they should have class A.

Mark
In my opinion Class A should be used by ships that often are not readily maneuverable due to size/draft/etc. A fast maneuverable "small" boat with shallow draft can get out of the way quickly so Class A isn't really a big advantage. For 50+ foot motor yachts Class A might be an advantage and may even be mandatory depending on local regulations.

There are 2,250 time slots per minute as I recall. Class A uses a lot of AIS time slots because when a ship is in "fast update" conditions they update every 2 seconds or 30 times per minute. So slots start getting used up fast in crowded seaways. Recreational craft that do not benefit from transmitting class A should not add to the clogging of the airwaves, again in my opinion.
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Old 25-12-2015, 07:48   #25
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Re: Vesper AIS SP-160 "relay/splitter" test results, lab/real world

Quote:
Originally Posted by Pelagic View Post
This got me thinking about how to wire up an AIS and its GPS so as to be a discrete tracker that could not easily be turned off by boat Thieves.

Has anyone done that?
What I have done is rigged my DSC VHF radio to automatically answer a "request for position". This will often have greater range than AIS. Unless the theives turn off the VHF then I can send a request for position via DSC and the ship VHF radio will send back the exact GPS coordinates. I have thought about some way to have a "hidden" DSC setup that isn't easily found. There are handhelds that can do this and I have thought of rigging one under a V-berth or somewhere inconspicuous connected to a dedicated VHF antenna.

If the fellow whose boat drifted away had this setup and he carried his DSC handheld ashore he could have asked the boat "where the hell did you go?" and it would have answered. I always take my DSC handheld ashore and not only for this reason.
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Old 23-01-2016, 11:12   #26
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Re: Vesper AIS SP-160 "relay/splitter" test results, lab/real world

hi to everyone, having read you first, and then here:
-------------------
Am I transmitting my vessel name? : Vesper Marine Support
-------------
i think that is better and safer to set up a second vhf (at this point ais tuned) antenna somewhere on a pole on the stern and run a good cable to the transceiver to avoid any delay in the trasmission in busy areas.
gp
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