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Old 20 January 2010, 15:41   #31
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I still think that radar's the most useful thing I have on my boat, after my ETec that is.
That's interesting. I've been wondering about upgrading my Garmin system with the radar unit, but was struggling to justify the cost. Do you find you're out in conditions when you need it, or is it more of an interesting luxury?
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Old 20 January 2010, 17:24   #32
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Do you find you're out in conditions when you need it, or is it more of an interesting luxury?
No, I've relied on it at least a couple of times when the fog has been really thick. We followed the yachts to Guernsey in last year's race. Off Sark the visibilty was less than 200ft but the radar showed multiple bogeys all over the place and we were able to keep going. The radar image can be overlayed on the chart plotter to help differentiate rocks from stationary vessels. This feature doesn't work too well at high speed because for some strange reason the refresh rate of the radar is faster than that of the chartplotter. I'm sure this glitch has been addressed on the new Garmin models or maybe I'm doing something wrong.

I don't know where you're based; my boat's in St. Helier. If you see me out and about give me a shout and you can have a look at the gear before you buy if you like.
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Old 21 January 2010, 03:41   #33
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This feature doesn't work too well at high speed because for some strange reason the refresh rate of the radar is faster than that of the chartplotter.
Which model do you have?

I would be quite happy to check through the settings the next time I am over.
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Old 21 January 2010, 04:50   #34
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AIS options

Note that the NASA AIS unit still does not monitor both channels simultaneously, though the Mk 3 now includes support for all AIS messages, which was not the case previously. From my AIS tests for the product review in December's Practical Boat Owner, the NASA unit was not a good performer, partly due to not receiving both channels in parallel, and also because you get what you pay for - great value for money, but you aren't paying very much so the performance won't be that good.

In my opinion it is worth going for a transponder if possible - I'd feel much happier if I was in a RIB in a shipping area if I knew that I would be popping up on the radar/ECDIS system of ships in the area - I can see ships easily, but they can't necessarily see me.

Note that some plotters (e.g. Raymarine) allow either NAVTEX or AIS input, not both - but I'd go for AIS and have a seperate NAVTEX display.

For the antenna, you can use your existing VHF antenna - splitters are available for both AIS receivers and transponders - but obviously you won't receive or transmit any AIS data when talking on the radio.

Tim
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Old 21 January 2010, 05:01   #35
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... and also because you get what you pay for - great value for money, but you aren't paying very much so the performance won't be that good.
True, and the Comar dual channel one is only about 170.00 so the "step up" is not that huge.

But the point is - how cheap does it have to be for various cruising areas?

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Old 21 January 2010, 05:12   #36
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Note that the NASA AIS unit still does not monitor both channels simultaneously, though the Mk 3 now includes support for all AIS messages, which was not the case previously. From my AIS tests for the product review in December's Practical Boat Owner, the NASA unit was not a good performer,
in real terms how much does no parallel reception actually matter? did you actually get real circumstances where vessels were consistently missing from the NASA screen that showed on others simultaneously using identical arials etc.?
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but you aren't paying very much so the performance won't be that good.
that argument doesn't always stack up and I would certainly expect that price is not a criteria for assessing performance (unless value for money) when someone rights magazine reviews.
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In my opinion it is worth going for a transponder if possible - I'd feel much happier if I was in a RIB in a shipping area if I knew that I would be popping up on the radar/ECDIS system of ships in the area - I can see ships easily, but they can't necessarily see me.
mmmm.... does that give a FALSE sense of security? my understanding is that (1) in busy waters the 'leisure AIS traffic' will be ignored to provide adequate space for 'commercial AIS traffic' - I'm not sure if you get a warning to highlight this is likely to be a problem (2) as I understand it not all large commercial vessels display the AIS data in an easy to read chartplotter screen - some (many?) simply list them in a table format. Does vessel XXX at WWW and NNNN heading BBBB at KKKK knots realy mean the skipper "sees" you - or just that he has a way of finding you if he tried to. Before "Zabaglioni" jumps to the defence of all commercial skippers - thats not a criticism of merchant seamen - its a comment on the expectation of leisure sailors that by transmitting a little burst of data every few seconds that they become visible or invincible.
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Old 21 January 2010, 05:18   #37
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In real terms how much does no parallel reception actually matter?
You will get less detailed data and some info is not broadcast that often and without a true parallel receiver there is a greater chance of missing the longer packet of info.

So in real terms you still get the important stuff - location, speed and heading. But in crowded waters you might have to wait for a new vessel's info to be fully populated.

Having said that I have not tested the new Mk3 NASA yet, so their software may be able to deal with this problem better now.
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Old 21 January 2010, 05:28   #38
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You will get less detailed data and some info is not broadcast that often and without a true parallel receiver there is a greater chance of missing the longer packet of info.

So in real terms you still get the important stuff - location, speed and heading. But in crowded waters you might have to wait for a new vessel's info to be fully populated.

Having said that I have not tested the new Mk3 NASA yet, so their software may be able to deal with this problem better now.
Ah but Malthouse - thats not what I asked! I asked 'in real terms' not the on paper answer which I understood. What I want to know is has anyone put this to the test (as you might expect a magazine reviewer to do before criticising it?) in realistic real life circumstances, and seen a significant issue. How crowded does it need to be - are we talking cowes week or the dover straights? Does it really cause a problem if you have to wait an extra minute or two to get 'full data' or see a vessel 5,10,15 nm away - bearing in mind that you are unlikely to be going full tilt in 'crowded waters'? And for the 99% of the waters which are never likely to be classified as 'crowded' is there an issue at all?

Edit: I have no axe to grind here and have never used a NASA AIS unit; but for AIS to gain widespread acceptance in the leisure boat community I think it needs people like NASA willing to push the price down, if necessary by skimming off any unnecessary functionality.
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Old 21 January 2010, 05:45   #39
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How crowded does it need to be - are we talking cowes week or the dover straights? Does it really cause a problem if you have to wait an extra minute or two to get 'full data' or see a vessel 5,10,15 nm away...
I have used both types in the Thames estuary, which is pretty crowded I think you will agree. Both worked quite well enough to be of benefit, but the NASA Mk1 did not report nearly as much detail the first time it picked up a vessel.

The only time I got confused with the NASA was when I saw a craft doing 70 knots in the area of Gillingham.
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Old 21 January 2010, 07:39   #40
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I have used both types in the Thames estuary, which is pretty crowded I think you will agree. Both worked quite well enough to be of benefit, but the NASA Mk1 did not report nearly as much detail the first time it picked up a vessel.
yes I guess that was my point - it works - it shows the vessels in a reasonably busy area. I think someone reading Tim's review may get the impression that actually the NASA unit doesn't really do the job.
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The only time I got confused with the NASA was when I saw a craft doing 70 knots in the area of Gillingham.
Was that the NASA or the output on the other craft though. i guess that is a failing on AIS in general - you rely on the transmitting vessel sending the correct info.
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