AIS CPA/TCPA

[phiggins]

To those of you who use AIS: what values do you set for the CPA and TCPA thresholds?

Thanks,

Paul

[donradcliffe]

On the open ocean I tell the crew to call me for any CPA of less than 5 miles.

[MarkJ]

Just so you dont leave the rest of us out of the discussion:

CPA - The Closest Point of Approach (CPA) calculation is performed if Fugawi is receiving your position from your GPS receiver. CPA is the distance you will be from an AIS vessel when you are nearest to it. The calculation is based on the current position, course and speed of your boat and each AIS vessel at the time of the last message.
TCPA - The Time to Closest Point of Approach (TCPA) calculation is performed if Fugawi is receiving your position from your GPS receiver. TCPA is the time (in minutes from now) at which your distance to the AIS vessel will be closest. The calculation is based on the current position, course and speed of your boat and the AIS vessel at the time of the last message. The TCPA will change when either vessel's course and speed are altered.

[phiggins]

Thanks MarkJ. And usually programs like Fugawi and SeaClear make the two an AND condition. In other words for example , Sound an alarm if the target will pass within 1 mile within the next 15 minutes.

But evidently some programs and chartplotters make them an OR condition which to me doesn't make sense. Who cares about a target that will come within 1 nm but that won't happen for 4 hours.

Paul