> my several years old car will scream with alarms if I'm closing on an obstacle, and eventually even start handling the danger for me. I have to assume the same systems exist for a huge expensive warship. So not only was the AIS turned off - all collision alarms etc were too?
I don't know how the military systems work, but I have used civilian maritime systems like the AIS you mention, some of which are built by semi-military manufacturers. Let me tell you, AIS is no silver bullet.
AIS does indeed alert us when another ship is within a predefined radius. But it does not judge whether the distance is closing or widening. If a ship passes perpendicular to our course but less than the defined radius behind us, we get an alarm--exactly the same alarm as if it were directly in front of us and moving toward us. There is no feature like "alert 10 minutes before expected collision."
Also, AIS has a feature where you can send messages as a broadcast to all nearby ships. The message you send could be "SOS SINKING 12 SOULS" or it could be "SATURN MICKEY WELCOME TO SALVADOR PORT" (a real one I saw last week with the names changed). The alarm at receiving stations will sound the same in both cases.
In busy shipping lanes there are multiple of these messages received per day by passers by, and several obviously-not-dangerous proximity alerts at the very least.
You can imagine why people might be inclined to turn them off.
If I understand correctly, AIS is only a transponder like system, so self-reported positions?
If you compare to any commercial airliner you have transponder for communicating some things, but you also have collision alarms such as the one screaming "TERRAIN" or "PULL UP" if you are about to smack into the ground. That system is a ground radar of some kind.
On a car the navigation system is also separate from the front collision avoidance radar thing that will scream at you if you are about to hit a slower car in your lane.
So from a lay persons perspective it seems absolutely insane that a warship wouldn't have several radar and sonar based collision avoidance systems in addition to (or perhaps working together with) any transponder/GPS (AIS) systems.
Yes, AIS shows self-reported positions. Basically it broadcasts your GPS coordinates, your ship's name and other details, plus (unfortunately) any random messages you want to send.
Ships have radar too. But my point here is not about sensors--the problem is in the human-computer interface. We can see on the screen that a ship is (or isn't) on a collision course with us, but the systems commonly installed on civilian craft only tell us if another ship is inside our predefined circle. And we have to make that circle fairly small when travelling in busy areas, or there will be alarms at all times.
Another fun, dumb thing about AIS: it does not self-report anchor state. It is a requirement that ships display a shape on their bow to indicate if they are anchored. But there is no dissemination of such data in AIS. It would be hugely useful to know the difference between a ship 0.5 NM away at anchor vs underway. And just imagine if we are ourselves in a busy anchorage--we would want an alarm if a ship underway is coming toward us, but not if a ship we are anchored next to is still exactly where we left it.
It's not that we don't have sensors to know what we need to know. It's that the displays and audible alerts are not ergonomically advantageous, and are prone to fatiguing their users.
There's also TCAS, which is transponder based and will negotiate with nearby aircraft also equipped with transponders - so if there's a collision risk, the TCAS in one aircraft will be saying "climb, climb" and TCAS in the other aircraft will be saying "descend, descend".
Or both TCASes might be saying "traffic, traffic" if someone else is nearby, and not on a collision course, but could end up on a collision course if one or both parties make course or altitude changes. So in this case it's a heads up to look for traffic nearby.
This doesn't take away from anything you said; I just wanted to point out that a solution based solely on self-reported positions can be quite effective too.
> it does not judge whether the distance is closing or widening. If a ship passes perpendicular to our course but less than the defined radius behind us, we get an alarm--exactly the same alarm as if it were directly in front of us and moving toward us.
I've used civilian AIS systems and I can assure you they can do exactly as you describe. It's called closest point of approach (CPA and TCPA)
> AIS has a feature where you can send messages as a broadcast to all nearby ships.
Consumer AIS does not do this. You are referring to DSC.
A consumer marine DSC/AIS VHF radio can send and receive DSC, receive AIS, and, if they have enough screen/CPU, can show CPA/TCPA tracks. For ocean passages we set our TCPA for 30 minutes and in port 2 minutes.
I don't know how the military systems work, but I have used civilian maritime systems like the AIS you mention, some of which are built by semi-military manufacturers. Let me tell you, AIS is no silver bullet.
AIS does indeed alert us when another ship is within a predefined radius. But it does not judge whether the distance is closing or widening. If a ship passes perpendicular to our course but less than the defined radius behind us, we get an alarm--exactly the same alarm as if it were directly in front of us and moving toward us. There is no feature like "alert 10 minutes before expected collision."
Also, AIS has a feature where you can send messages as a broadcast to all nearby ships. The message you send could be "SOS SINKING 12 SOULS" or it could be "SATURN MICKEY WELCOME TO SALVADOR PORT" (a real one I saw last week with the names changed). The alarm at receiving stations will sound the same in both cases.
In busy shipping lanes there are multiple of these messages received per day by passers by, and several obviously-not-dangerous proximity alerts at the very least.
You can imagine why people might be inclined to turn them off.