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Old 08 February 2010, 02:14   #1
Channel Ribs's Avatar
Country: UK - Channel Islands
Town: Alderney
Length: no boat
Join Date: Sep 2006
Posts: 3,047
A follow up on AIS (Class B this time)

This letter from a Solent Harbourmaster has been linked to on YBW, it is two years old now but I fancy the views are probably still valid and well balanced:

"I have discussed the issue of 'active radar reflectors' with some of our VTS staff and Pilots and hopefully can give you a steer - I must emphasise that the following are my own assessment and views on the matter and not port policy - I have no particular axe to grind for either 'active radar reflectors' or AIS B equipments.

That said, as a port authority, we do have an obvious interest in being able to see all vessels navigating in our area - by all means (visual, radar, AIS etc) - and in their navigational safety.

There are a number of considerations here but, having made the comparison on what each has to offer, I would say that within busy coastal waters, such as The Solent, the 'active radar reflector' is likely to be a better choice. This enhances your radar echo and improves your chance of being seen by commercial vessels - particularly at night. I don't think it gives false confidence to the user, in terms of your being seen, and still requires you to navigate with caution and to maintain a good lookout. Additionally, your enhanced echo will be seen on any X-Band radar, cannot be filtered out, and does not need any additional equipment or watch from the bridge watchkeeper. Remember, many AIS equipments are still stand alone and not integrated into navigation suites - so they may not be monitiored in busy shipping situations.

As far as AIS B is concerned, on other hand, in busy areas - again, The Solent, for example - it seems that many vessels do chose to filter AIS B out of their AIS picture - and for obvious reasons. They will have it activated for offshore and ocean waters but, once closing the coast, will switch AIS B responses off. Indeed, as I said in my presentation, AIS B is becoming cheaper and more popular, but Southampton VTS often has to filter it out, otherwise the central Solent picture becomes very cluttered. The advantage AIS B does have over the reflector, is that you get to see other vessels' information but, remember, if the equipment is not integrated into your navigation suite it is providing CPA's etc using only GPS and 'simple' mathematics.

If you are likely to be sailing largely within The Solent area and adjacent coastal waters, I would say that the 'active radar reflector' is probably the better choice - for the reasons above. If you are a cross-Channel sailor - or go even further afield - I would say that AIS B will probably be of better assistance - as many more ships will have AIS B signals activated in those areas and your AIS message should be seen."
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