Another AIS Antenna Question!

Re: AIS info superimposed on \'proper\' RADARs

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Is ARPA as opposed to MARPA available yet?

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Not quite sure what you mean by this. MARPA is Mini-ARPA only in the sense that it's limited to tracking 10 targets. I rarely engage more than 4, even crossing the shipping lanes

The fast heading compass could be the rate gyro, I'll be using a Honeywell sensor which knocks the spots of anything else we've ssen
 
I have direct experience of both the vtronix helical antenna and a 1.1 m whip from JGtech (cheapest on the market)
Both mounted at pushpit level.

Helical was very disappointing - 7nm average with a bets of abt 10m on a BIG ship.

1.1m whip - average abt 13-15nm with some responses at well over 20nm.
 
Re: AIS info superimposed on \'proper\' RADARs

I suppose I'm a bit old fashioned but I would have altered course - though I am not saying you are wrong, in fact you were the stand on vessel. I don't think I'd call them either unless in extremis.

If yachts have all the details to call them, ships will get quite a few calls from yachts. I wonder what how the pros feel about this; "an aid to safety" or "a bit inconvenient at times".
 
Re: AIS info superimposed on \'proper\' RADARs

Can you let me have details of the Honeywell sensor and any special wiring details, if they are to hand?[ QUOTE ]
MARPA is Mini-ARPA only in the sense that it's limited to tracking 10 targets. I rarely engage more than 4, even crossing the shipping lanes

[/ QUOTE ]I might be wrong, but I thought the the 'M' in Marpa stands for 'Manual' and that ships' systems automatically plot and display all targets, together with a CPA alarm? If not, it is certainly a function that would improve safety since you might have a collision with a target that wasn't painting until the last mile or so, and may not have been selected on the MARPA/ARPA.
 
Re: AIS info superimposed on \'proper\' RADARs

we were stand-on both because we were on his starboard bow and sailing. i was reluctant to bear away to starboard as we were already further west than I wanted to be. the radio waves were not exactly crowded with boats talking to ships - i don't see a problem with it.

when we reached the W-E shipping lane, we were on the port bow of another ship and although still sailing but he wasn't to know that so we chose to change course to be on the 'safe side'.
 
Re: AIS info superimposed on \'proper\' RADARs

Honeywell details here from TDC

M stands for Mini. It would take a huge amount of processing power to auto-track targets without manual initiation, though I believe it is now available on IMO sets (big ship stuff!). Even then there are anecdotal tales of the pros switching off the auto-acquire feature and reverting to manual
 
Re: AIS info superimposed on \'proper\' RADARs

Just to be clear, my reply wasn't intended to be an adverse criticism. I am just musing about the changes now that yachts can simply call up ships to discuss these things. Until AIS it wasn't possible as by the time you could read the ship's name you have sorted out what is going to happen! And probably no yacht would mess about with "calling the vessel in position XXXX travelling a YY kts on a course of ZZZ" because of the hassle factor and, I guess, the inability of the majority to work it out in any case /forums/images/graemlins/smile.gif
 
Re: AIS info superimposed on \'proper\' RADARs

That's a fascinating range of sensors. I could have great fun with those position sensors. But I couldn't see a rate 'gyro' or is that available as an output from one of them? I thought that the Raymarine radars were looking for something that they call a 'gyro' input which is actually a solid state rate of turn device with presumably a known fixed output of X volts per degree per second?
 
Re: AIS info superimposed on \'proper\' RADARs

Raymarine radars are happy with NMEA input. The term 'gyro' is just used by Raymarine to signify a fast (10Hz) input
 
Re: AIS info superimposed on \'proper\' RADARs

Do you mean a 10Hz compass input or rate input?
 
Re: AIS info superimposed on \'proper\' RADARs

I've been looking into this in a bit more detail on the Raymarine website and it seems that the rate gyro unit Gyroplus 2 takes the standard fluxgate input and provides a fast(er) NMEA heading sentence output plus a rate signal of 22mV/degree/second. In my case, I have a course computer that requires the 22mV rate gyro input, so none of the Honeywell sensors on the page you gave a link to, would work.

Unfortunately in my case, to wire in the rate gyro I would need to run an extra cable along a very trick path. It is the sort of job you try to do when other major work needs to be done rather than pull everything apart for a non-essential part. So I will live without.
 
Re: AIS info superimposed on \'proper\' RADARs

I'm guessing here, but suspect the rate input is only used to increase the frequency of updates. Rate gyros have good short term but poor long term stability/drift so it makes sense to use them to provide incremental inputs to the slow but more stable fluxgate compass Raymarine use

This being the case, you can achieve the same thing with a high-speed compass which I believe would render the analogue rate signal superfluous. The Honeywell unt is actually a 3 axis magnetometer and we've evaluated it against a conventional high speed survey fluxgate and a conventional gyro. Results were very good, particularly with respect to heading stability v pitch and roll where conventional fluxgates struggle
 
Re: AIS info superimposed on \'proper\' RADARs

The Raymarine radars are happy with the high frequency heading string alone but if you have certain Raymarine autopilots, notably ones with course computers external to the 'head' then you are supposed to wire the 'gyro' 20mV/degree/second signal into the course computer. So in my case I need to feed the fluxgate into the Raymarine gyro which then outputs a high frequency heading string and the dc signal output. I haven't got enough spare cores in the cable /forums/images/graemlins/frown.gif

Interestingly and oddly, it seems that if you link the gyro to the radar via Raymarine's proprietary SeaTalk link the link is slower than using NMEA - which seems odd so needs to be double-checked in case I misread it.
 
Re: AIS info superimposed on \'proper\' RADARs

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Interestingly and oddly, it seems that if you link the gyro to the radar via Raymarine's proprietary SeaTalk link the link is slower than using NMEA - which seems odd so needs to be double-checked in case I misread it

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You didn't misread it, the Seatalk heading updates are limited to 2Hz
 
Re: AIS info superimposed on \'proper\' RADARs

I have the Raymarine C120 interfaced to a 2Kw raydome and a NASA AIS - on crossing the Channel to Cherbourg recently the radar reflections and the AIS appeared to be quite well aligned even with fast shipping - certainly no worse than a buoy or other reflection out on the water...screen shots here..
http://altendorff.co.uk/category/sailing-hardware/ais/
 
Re: AIS info superimposed on \'proper\' RADARs

Interesting to see that there are no shots of AIS/radar alignment on your site, no?
 
We also have a NASA AIS Radar, and have been using it for two seasons. We use a conventional whip aerial mounted on the pulpit, although we are planning to put an aerial post on the starboard quarter to take all our aerials, including GPS, Navtex, etc.

But our AIS aerial is also our emergency VHF aerial. The VHF aerials (masthead/pulpit) are connected in to the VHF and AIS sets via two coaxial change-over switches. In the event of us losing our masthead aerial we swing our switch panel down and reverse the two switches. We lose our AIS (at least, temporarily) but regain the use of our VHF, albeit on reduced height and range. But our AIS regularly shows up ships at 16 mile range, so we might expect a similar range on VHF.
 
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