oldvarnish
Well-Known Member
Not for you, and not for me. But corporate culture says anytime is the right time for paperwork.
Class B makes you that confident?
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Not for you, and not for me. But corporate culture says anytime is the right time for paperwork.
pvb
Well-Known Member
Meaning what?
prv
Well-Known Member
Meaning that I find it unlikely, and haven't seen any evidence to back up the frequent claims.
Pete
pvb
Well-Known Member
Ship radars installed since 2008 have to comply with the provisions of IMO resolution MSC192(79), which you can read at http://www.imo.org/blast/blastDataHelper.asp?data_id=15568
It contains lots of provisions for filtering out Class B AIS targets.
In 5.26.1 it actually says "Reported targets provided by the AIS may be filtered according to user-defined parameters." This provides for filtering out Class B targets.
Then in 5.26.3 it says "To reduce display clutter, a means to filter the presentation of sleeping AIS targets should be provided, together with an indication of the filter status. (e.g. by target range, CPA/TCPA or AIS target class A/B, etc.)." This confirms that Class B targets may be subject to being filtered out.
Again, in 5.26.4 it says "In addition, sleeping AIS targets may be automatically activated when meeting user defined parameters (e.g. target range, CPA/TCPA or AIS target class A/B)." Once again, we're reminded that Class B targets may be filtered out.
So, clearly, in setting the new specifications for ship radars, the IMO recognised the potential need to be able to filter out Class B targets. Realistically, this should only happen in crowded waters, in order to make it easier for watchkeepers to interpret the screen. However, having set the filters, there's no guarantee they'd disable them once in open waters. Having a Class B transponder is no guarantee of showing up on a ship's radar screen. A better investment is an active radar reflector.
johnalison
Well-Known Member
I have had an active radar reflector for many years but when I fitted a class B transponder three years ago I never intended that it should be my only means of showing myself to a ship, only that I could never be worse off for having one.
pvb
Well-Known Member
Exactly! And that's the right sequence for fitting these safety aids. An active radar reflector should ensure you're seen by ships. A Class B transponder might, or might not, depending on whether the ships are filtering out Class B targets.
oldvarnish
Well-Known Member
How sensible
BrianH
Well-Known Member
TB used to strongly refute any suggestion of Class B filtering and he used to write books on the subject - not that that necessarily made him correct. However, I believe he may have been insomuch as I have always understood that any so-called group 'filtering' pertains to target display and that any threat appearing within CPA adjustable boundaries will enter the display parameters regardless of class, as all targets remain in the target list.
If that is a correct presumption then "having a Class B transponder is no guarantee of showing up on a ship's radar screen" is only relevant for non-threat targets and it is still worth having for when emerging into a threat position. I would appreciate being corrected if wrong.
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pvb
Well-Known Member
No, CPA/TCPA alarms can be disabled for Class B targets.
BrianH
Well-Known Member
Thank you ... surprised :disgust:
ShinyShoe
Well-Known Member
Well that probably didn't work. The inference in the MAIB report is he was dozing in a chair. If I'd been doing paperwork I'd have told them and told them the culture was I had to to keep my job. None of that explains why they had 1 man on the bridge even though crewed for 2, or why when you cock up you don't call the master to tell him.
He is darned lucky no one was hurt.
BrianH
Well-Known Member
So surprised that I did some searching for information and came across a Panbo issue that has a contribution from the AIS Guru, Dr. Andy Norris, that was interesting: http://www.panbo.com/archives/2010/12/class_b_ais_filtering_the_word_from_dr_norris.html#more
Asked if he himself recommended small ships using Class B transponders in the light that their signals may be filtered, Dr Norris answered:
"My view is that is preferable for recreational craft to carry and use AIS Class B transponders.
This makes craft highly visible to an ever increasing number of ships in normal circumstances. It does not guarantee that you will be observed on a particular ship's AIS system but it increases the chances way above 0%, which is what happens if you don't use an AIS transponder.
Remember that a ship's radar will not be guaranteed to see you either, neither are you guaranteed to be seen from the bridge windows. However, the chances of being seen visually, by radar or by AIS will be greatly increased compared with relying on just visual and radar visibility.
Safety at sea, just as when driving, is governed by probabilities, not certainties. We need to be always decreasing the probability that an accident will occur to us, as individuals."
For me, the transmission part of my AIS installation is not the main interest, the receive function is. To see just what an approaching ship has as a course compared to my own is very useful.
pvb
Well-Known Member
I've got no issue with yachts having AIS receivers, I have one myself and find the information displayed on the plotter useful. But what worries me is the way leisure boaters have adopted Class B AIS transponders in huge numbers, believing that it magically makes them visible to shipping. Out in the ocean, maybe it will, but in the inshore waters many of them operate in it won't.
It was obvious from the beginning that widespread take-up of Class B transponders had to lead to ships simply filtering them off their radar screens. I've put that view forward in these forums a number of times over several years. The screen clutter in crowded waters makes it essential for ships to filter out Class B targets.
In the Panbo article you refer to, Dr Norris also says "Particularly in busy areas, small craft often pass closer to ships than is generally considered safe for ship-to-ship encounters, even though needing particular alertness by the small craft skipper. For this reason, especially in areas that are crowded with small craft but that also have appreciable shipping movements - such as in the Solent area of the UK - it could well be the case that any activation of Class B targets will cause almost constant activation of the Closest Point of Approach (CPA) alarm on the ship - continually distracting the navigating officer/pilot. A 1.0 NM CPA may be appropriate for ship-to-ship encounters in such an area, but many small craft skippers will be quite happy approaching ships at very much closer distances. Therefore, filtering of all AIS Class B targets, together with preventing their activation, may be the appropriate strategy in such areas to avoid possibly dangerous alarm distraction of the bridge team."
Anyone wanting to ensure that they'll be seen on a ship's radar screen is far better off buying an active radar reflector. They can't filter that out!
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BrianH
Well-Known Member
Fully agree. I too have lamented the proliferation of unnecessary Class B transmissions on these forums, citing the fact that I now have to totally disable my CPA/TCPA alarms that needed constant resetting due to the burgeoning number of Class B signals in the Adriatic. That is negating what had been a very useful function in waters populated by high-speed ferries that are a definite hazard.
Needless to say, I only enable my transmissions when appropriate and not in congested waters.
pvb
Well-Known Member
Sadly, leisure boaters don't have the luxury of filtering out Class B targets! Unless, of course, we buy rather expensive ship radars...
sailorman
Well-Known Member
rather like LED running lights on new vehicles, everybody else gets blinded by them, thus defeating the point of having them
johnalison
Well-Known Member
That looks like a way of justifying to oneself the decision not to fork out on buying one! I have no difficulty in accepting that there will always be people who don't want class B, or who can't afford it but to date, after three years regular use, including a visit to the Solent, I have yet to find myself in a position where an excess of signals from small craft caused me any difficulty.
I suspect that one reason for my indifference to the problem is that I have an up to date plotter, an e7, with a fast redraw time and so it is easy for me to change the scale of the chart to clarify my situation. I'm afraid there is no point in people worrying about it because the situation is not going to change.
Lucky Duck
Well-Known Member
I have a similar plotter (C125). However, the issue for me isn't the screen 'clutter' from class B but that they keep setting off the CPA alarm meaning that until Raymarine offers a software update which allows the alarm to discriminate between Class A and B units the alarm remains firmly switched off in places like the Orwell.
pvb
Well-Known Member
I don't see it that way. Isn't it more a case of spending effectively? A Class B transponder is £450 - the same as a Sea-Me or Echomax Active radar reflector. The difference is that the active radar reflector always works to enhance your visibility on ship radars, whereas the transponder might, or might not, depending on whether the ship is filtering out Class B clutter. It's a no-brainer.
jerrytug
N/A
Echomax RTE, X-band only, £360 new on ebay, even more of a 'no-brainer'!
