AIS & ARPA ...

[Robin]

Re: AIS & ARPA ...

[ QUOTE ]
The place for radar on a small craft is at the helm.

1) Familiarisation , helm can see what's happening + radar
2) Shorthanded
3) Don't need concentration and no distractions from other activities, all you need is an EBL and see if the target is moving in front or behind the EBL .. or is that too simplistic? I start to watch at 10 miles & take action at 5, if its a bunch of boats I'go behind them. In fog I'd rather add an hour to my journey than pass less than a mile from a large vessel.

[/ QUOTE ]

1) OK no argument

2) We are ALWAYS shorthanded. There is only ever me and SWMBO. In fog she is eyes and ears up top and I work the radar, plotter and the autopilot from below. SWMBO can also understand and use the radar but in extremis prefers I do it.

3) Yes that is too simplistic IMO. I agree with 1 mile minimum ( but see previous posts re CPA which may be entirely different and paper doodling is required to explain). The EBL is fine, as long as it is set whilst you are ON course and it is checked when ON course. However the EBL is not the entire story because it doesn't tell you the 'aspect' of the other vessel, you need to plot it if you want to see that and get it's course and speed. Trouble is too that sometimes one EBL isn't enough..... Our routine is to watch on 6 mile range as a routine and drop to 3ml for closer approaches. Watching at 12 mls carries the risk of missing small targets perhaps. I don't take action until we are on 3ml range and even then with care bearing in mind what would happen IF that ship altered course too as well as what the next target is doing, it is easy to dodge one and get in the way of another previously not of concern. Avoiding a bunch of boats sounds sensible but in practice is very difficult because you think they are limited to a bunch when in practice there ARE others, just they are not on your screen yet. In the Dartmouth/Ushant scenario I used as an example you would never get across if you adopted that tactic because the procession is endless!

A McGregor 26 would be nice, just blast across out of the way as quick as possible /forums/images/graemlins/laugh.gif

 

[Robin]

Yes it does go crap as you say although you can get some improvement by switching on the 'rain' and turning down the gain a tad. It's OK if you already know that particular target has cleared, hence another reason not to go closer than (say) 1 ml ahead, BUT the CPA may still occur sometime later and within the crap circle.

 

[jimi]

Re: AIS & ARPA ...

However the EBL is not the entire story because it doesn't tell you the 'aspect' of the other vessel, you need to plot it if you want to see that and get it's course and speed.

I don't need to see that, all i need to see is its movement realtive to my own and assuming a constant heading then the forward or back of an EBL is sufficient


Trouble is too that sometimes one EBL isn't enough.....

True .. but usually easy to monitor targets of interest.

My perception is that its not usually the awareness that's the problem its the subsequent actions

 

[Robin]

[ QUOTE ]
you're getting dangerously close to proving my point .. that's 33 odd ships (one must be at anchor?) for which you could generate data thro' AIS and all from an aerial which must be on land ?

[/ QUOTE ]

I hope you didn't put all 33 into the probability equation though! I don't know where AIS Live get their data, I suspect perhaps not via an aerial in every location they monitor round the world?

[ QUOTE ]
Being a mathematician, and if this was fog, the probabilities of successfully crossing that lot have immeasurably improved and that's what I've been banging on about ....

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Yes but you don't have to cross that all of that lot do you, just those that are in your little bit of the Channel at the same time as you are! The reality is that although you can SEE seemingly endless streams of ships whether by mk1 eyeball or by radar (even AIS...) only a few of them will be of real concern. Many will have passed your location/track already, or quite plainly will pass it. Likewise others will be long clear ahead by the time you get there. The strange thing is that the 'problem' one is usually not one in the immediate area at all but is only just coming into view, visual or radar view.


I'm not saying AIS isn't a good thing to have either, just that it should be 2nd priority after the radar. I am acutely aware that we have had near misses in fog but pretty well all from small stuff which we didn't apply the same exclusion zone circles to! Like the 25kt radarless twit in a sports cruiser at N Head buoy in 20m vis who was on his mobile phone as he went by spraying water into our cockpit. We only picked him up at 0.75mls as he was in stealth mode ie grp boat, no reflector and head on to us.

 

[ghostwriter]

what good are messengers if you can\'t even shoot them ?

is AIS a gadget ? don't think so, think it's a bit beyond gadgetry level. I really think it has a potential to beat the good old radar, or at least come to a same level. if "all things afloat" can talk to one another saying simply "this is who/what I am, this is my position, this is my direction and speed" without all the complications you have with radar (which only works well when you don't need it, and always goes quirky at moments when you need it), you have a winner.

theoretically there is indeed a potential to turn it into big brother's preferred gizmo, amazing to see from the other side of the channel how uptight you guys always are about these things....trust your governement I'd say !!
/forums/images/graemlins/laugh.gif (but I wouldn't say in what direction you should trust them /forums/images/graemlins/wink.gif )

the question is indeed if we want to exploit the full potential knowing there might be openings for big bro's use, but if you put things in the balance, and when you consider the masses of yotties that might go in against the MCA's of this world, I'd still favour the full development of AIS.

 

[ParaHandy]

Re: what good are messengers if you can\'t even shoot them ?

"always goes quirky at moments when you need it" ... given how suddenly an english (oops La Manche!) channel fog descends followed by a quick scurry down below to switch the thing on, i agree with you. You fiddle with the gain and then rain and start to worry ...... when handbooks, commercial ships etc describe using radar, they typically are using it all the time and, presumably, adjusting it for the current conditions continuously ...

 

[ghostwriter]

even worse

the problem is even deeper than handbook knowledge or continuous adjustments for current conditions ... even with the best of handbook knowledge, and the best trial at adjustments, can you at all times be sure that you are seeing all possible targets ?? on a flat & calm sea probably yes, but then you don't need it, on a rollercoaster foamy sea with your 30 foot yot going all over the place, with your clutter controls that can't handle the rain, the spray...what do you see ? and believe you me, it's not all that better at the bridge of that 500 foot containermonster that comes bearing down on you, that much I can vouch for, I have had heroic discussions with deck officers about the way they were handling the radar, the sometimes incredible arrogance with which they claimed their settings were o.k. and next they nearly ran over a fisher, the problem was not necessarily that their settings or education was wrong, the problem is more that at a certain moment radar just can't handle it.

the problem is in the radar basics itself, and next you compare it with the relative simplicity of just a whip antenna receiving simple coded VHF messages of whatever floats in the vicinity.... I dare to claim that this might be better and safer.

wasn't it YM that just did a radar test (set up by none other than "Ollamby ?? ) ... I would dare them to do the same test in a healthy F7/8 with a good seaway and some rain thrown in for good measure, now THAT I would like to read.

and for those still gung-ho on the potential AIS big brother theme.... from the moment you switch on your cellular phone, big brother knows where you are within a range of +/- 100 meters, so what's the problem if they know where you are on your yot ?


stepping off my soapbox now /forums/images/graemlins/blush.gif