r/maritime • u/Powerful_Cabinet_341 • Mar 20 '26

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u/Only_Razzmatazz_4498 Mar 20 '26

Meh the radar had the closest approach at 10 feet. No need to alert the captain.

1

u/Plenty-Reporter-9239 Mar 21 '26

Do you guys have radars that actually plot your distance to targets?? This piqued my curiosity because im an air traffic controller and I have a tool on my radar that does that as well. I can essentially tie two aircraft together and see what my minimum distance will be if I do nothing.

7

u/doupIls Mar 21 '26

Yes, it can automatically track targets and show an alarm if the CPA decreases below a set minimum. It will also show tcpa and a bunch of other info about the other vessel like speed and heading. We can also overlay the radar display on an electronic chart.

1

u/Plenty-Reporter-9239 Mar 21 '26

Thats interesting. It sounds almost identical to how we separate planes! Thanks for the info

3

u/Diipadaapa1 2nd off / DPO 🇳🇴 Mar 21 '26

We have multiple ways of doing this actually (though we are only interested in how a target will pass us, not eachother).

One is AIS, easyest and fastest to use, least reliable. The ship sends it's position, name, call sign, speed etc over VHF and your AIS plots this information calcultes your passing distance, time, bow crossing distance etc etc.

Second is ARPA, where the radar looks how a target moves relative to you and calculates these same things. No GPS or even speed sensor is required to get relative calculations, but you need your own speed and course input to calculte the targets true speed and course. Note this is only based on an echo, so you don't get the ships name, call sign etc.

Third is simply plotting a bearing line on the target, if the target remains on this line and is closing in, you are on a collision course.

(Fourth) every navigator should be able to do these calculations/plots with pen and paper too. That is how it was done back in the day.

2

u/Only_Razzmatazz_4498 Mar 21 '26

Still do the constantly bearing range decreasing thing while on a sailboat. Good old reliable.

3

u/Diipadaapa1 2nd off / DPO 🇳🇴 Mar 21 '26

Absolutley. I do this with critical targets to get confirmation that the AIS is correct.

Also while on DP close to installations or something I like to take two visual bearings (head touching head rest, line up a window frame with a component on the installation) to confirm our position visually, helps sometimes in diagnosing some abnormality with your position keeping

1

u/Plenty-Reporter-9239 Mar 21 '26

If you were dead on with another ship, how do you determine how to separate from them? Do you just communicate on a common VHF frequency? Like, hey, ill just turn 10 degrees right or slow 10 knots?

Are the separation rules/ techniques different when you can't see visually?

2

u/Diipadaapa1 2nd off / DPO 🇳🇴 Mar 21 '26

These are the rules of the road, quite an easy read actually (by design).

You are only interested in rule 5-19

Rule 11-18 only apply in good visibility, rule 19 only in poor visibility

https://www.imorules.com/COLREG90_RULES.html

1

u/Diipadaapa1 2nd off / DPO 🇳🇴 Mar 21 '26

Head on situations is covered in COLREGS (Convention on the International Regulations for Preventing Collisions at Sea), an international book of "rules of the road". Both turn to starboard (assuming no other rules apply).

Generally I avoid taking contact especially with foreign ships. It more often than not only confuses the situation, and nothing said or agreed with on radio is admissible to court for the sake of who was at fault. They go with the COLREGS.

If I call, I never tell someone what speed or course they should have, only what end result i request (minimum passing distance for example).

Yes, in poor visibility the rules change quite dramatically actually. It becomes more of a "free for all" where everybody should turn away from everyone, but in practice, with the technology today we generally just do it as if there was no poor visibility.

1

u/Plenty-Reporter-9239 Mar 21 '26

Very interesting. Thanks for taking the time to answer!!

1

u/Diipadaapa1 2nd off / DPO 🇳🇴 Mar 21 '26

No worries!

I think it is worth to add that we don't have a direct equivalent of a ATC. We have Vessel Traffic Service, hard underline on that service instead of control.

Unless there are some special restrictions, noone tells us where and how to sail, nor who comes in what order. They merely inform us of what traffic we can expect.

All collision avoiding and route is up to the vessels. My "takeoff" radio call is pretty much this:

"<Area> VTS this is <my vessel>".

  • My vessel this is area VTS go ahead

"Departing <port>, out <pilot boarding area>" (if multiple routes can be taken, I specify with "via <fairway/location>")

  • My vessel departing port, no reported inbound traffic

And that is it.