AIS saturation

" The NASA AIS engine does not offer the ability to filter out transmissions from class-b devices"

The nasa ais radar shows class B vessels with a different icon which is very helpful.
 
When away from the constraints of the inner Solent, I normally set exclusions of within 2 miles and 30 minutes. This matches most officer of the Watch to Commanding Officer constraints.
 
I think from a big ship point of view you are missing the point here.
If everything from a rubber duck upwards fits AIS B and are all transmitting anywhere near one of the ports you mention it will become so cluttered that you will HAVE to switch off AIS B to get rid of the noise and so will port control. It's fine saying people should only transmit under certain circumstances but I am sure they won't. Your example of DSC radio relays is a clear case in question. It requires people to use it intelligently. It's obvious from posts here already that they won't. The example of a yacht transmitting while racing is typical.
 
Interested Mark why you set these limits. Knowing you you have a reason, can you expand please? Assuming a tanker is doing say 15 knots 2 miles will be covered in circa 8 minutes also a fast ferry doing 35 knots will be over the horizon and long gone in 30 minutes. I had felt for channel crossings 5 miles and 20 minutes would give enough warning to take evasive action for both cases. I am really basing this on the fact that it's my speed that matters and if I can do 6 knots and am on a collision course, 20 minutes gives me time to be 2 miles away from the scene of the accident if I make a sufficient course correction. Have I missed something here?
 
Its if the Closest point is 2 miles - this will warn you as soon as the AIS unit picks up any vessel that will enter a 2 mile radius of your boat in the next 30 minutes .... even if they are currently 15 miles away.

Whilst we're on AIS alarms - it would be handy to be able to grade them ... so a warning beep at 2 miles, and an alarm at 1 mile (or other user defined distance/time) - it was the one thing that annoyed me about the CP180i unit - that the AIS alarm sounded until it was no longer a threat or you cancelled it, if you cancelled it and it stopped being a threat and then was again (even within 10 seconds) then it would sound again - so we had a lot of alarms all which were on the fringes of our guardzone (1Nm) - so annoying I turned the alarm off.
 
Oh! hang on here, I am unashamedly new to AIS operation. I had assumed that we had closest point of approach and time to closest point of approach so the alarm was EITHER time based OR distance based whichever was least. I think what you have said is set the alarm distance as the closest you want to be to anything and the time as the time it takes to get that close..... I think that makes more sense and may explain why I got an alarm from the ferry docking in Portsmouth which briefly pointed up Fareham Creek (Doh!)
So if I set the distance to 1 mile and time to 20 minutes (for example) then the alarm will sound if the bogey looks like taking 20 minutes to be within a mile of me? Have I got it right this time?? Actually that makes sense of Talbots post too.
Thats what happens when wrinklies are faced with new techie things see.... miss the blindingly bleedin obvious!!
 
Erm - I'd check the documentation - I haven't bothered using the Time element ... jsut the distance ...

from the CP180 manual:

14.0 AIS SYSTEM DEFINITIONS
♦ Target: It is a vessel equipped with AIS. Information about the targets is being
received by AIS Receiver and displayed on the screen.
♦ CPA : Closest Point of Approach is the closest distance that will be achieved
between your vessel and the tracked target, based on your vessel’s speed and
direction and the target’s speed and direction.
♦ CPA Limit: This is the distance from your vessel that a target may reach before
a target is deemed a threat.
♦ CPA Alarm: Occurs if CPA is less or equal to CPA Limit. This test is done for
active targets only.
♦ TCPA: Time to closest Point of Approach is the time remaining until the CPA
will occur.
♦ TCPA Limit: This is the time remaining before the CPA is reached.
♦ TCPA Alarm: Occurs if TCPA is less or equal to TCPA Limit. This test is done
for active targets only and if CPA value is less or equal to CPA Limit.
♦ Radio Call Sign: International call sign assigned to vessel, often used on voice
radio.
♦ Name: Name of ship, 20 characters.
♦ MMSI: Maritime Mobile Service Identity.
♦ MMSI number: A unique 9 digit number that is assigned to a DSC radio station.
It primarily registers the boat information in the U.S. Coast Guard’s national
distress database for use in emergency situations.
♦ Active Target: Target located within the Activation Range. Active target is represented
by oriented triangle with COG and Heading vectors. Rate of turn may
also be displayed.
♦ Dangerous Target: Target detected by CPA or TCPA Alarm. Dangerous target
is Active Target by definition. For better visibility Dangerous Target symbol is
flashing.
♦ Sleeping Target: Target located outside the Activation Range. Sleeping target
is represented by a small oriented triangle.
♦ Lost Target: When the AIS info is not received from that vessel for 3.5 minutes.
The presentation will be a flashing black triangle with a cross through.
♦ Activation Range: Range around your boat where targets become active. AIS
target become active within this range. Activation Range should be greater
than CPA Limit by definition.

So - CPA Limit is the distance - radius of the circle - which Talbot sets to 2Nm ...
TCPA - The to closest point of approach - which Talbot sets to 30 mins - so if a vessel will be within 2Nm of him in the next 30 mins then it will alarm.

If you don't have a Standard Horizon CP then CHECK your instructions - it may be different (sods law says it will!)
 
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