AIS CPA Alarm

AIS is a wonderful invention that allows your radio to display all the vital information of any other vessel that is broadcasting AIS.

This changes a night time encounter from plain navigational lights to something more useful, like the vessels name, speed, and heading. With this information, the computer in the radio can also calculate how close you will come and when this will occur.

Closest Point of Approach (CPA) is very helpful. It will tell you if that ship on the horizon is going to be a problem, or if they will stay far away. Best of all, some radios have alarm features, so if a ship will come too close, it will sound a very loud audible alarm to bring the situation to your attention.

We usually set the alarm to 2 nautical miles when we heave to at night. This gives us plenty of time to wake up from the alarm and rectify the situation. Two years ago, when we set out into the Atlantic, the other ships were very courteous, always responding when hailed and being more than accommodating  to avoid a collision.

This year though, it seems that no one wants to answer. We have done a radio check, and other boats far away can hear me loud and clear, but they just seem to play the silent game.

Seeing a massive tanker approach you at 20 knots can be a bit unnerving, especially when you are hove to with no wind to move you if you needed to. At night, I have found one tactic that seems to get an instant response when words fail: a strobe spot light.

You know, those "tactical flashlights" that they sell with the high powered LED light and focusing lens. These things are bright! I simply shine it in their position and then up at the sails. Then when I go below deck to check the AIS display, they have inevitably changed course and steered away from a collision course.

This alarm does not replace a good watch schedule, as not all vessels transmit AIS, but it does alleviate the anxiety of wondering if you are going to bump into someone while you sleep between watches.

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