AIS CPA and TCPA for Solo Sailors

[GILow]

On the last trip from Melbourne to Adelaide in early 2013 we were passed by maybe a dozen ships in any 24 hour period. Looking at the marine traffic density maps I’d guess most of those would have been coming to or from the southern tip of Africa.

I do remember it got quieter after we’d gone around the corner from Portland. Though, of course, there was a whole bloody armada ready to go through Backstairs Passage at the same time as us. Bastards!

Was thinking of going a bit west after Backstairs Passage in part to clear the shipping lane but also to get the smoother ride away from the continental shelf. Had forgotten that deeper water also means no lobster pots. Might go even further west.

[mgl]

Originally Posted by GILow

While there seems to be quite a bit of discussion around solo sailing, one question I have not found directly addressed is the issue of AIS CPA (Closest Point of Approach) and TCPA (Time to Closet Point of Approach) alarms for the solo sailor.

I would love to hear from solo sailors and others on their preferred settings for the two alarm thresholds and the logic behind their choices.

Stop worrying about acronyms, AIS is brilliant for the solo sailer. If set up properly you can see vessels up to 40 miles away. More importantly they can see, you, always get a unit that transmits , set your vessel up with the correct identification and you will see in the middle of the night that approaching vessels slightly changeing course to avoid any chance of a collision.

I simply set the alarm to go off for any vessel in a 20 mile radius and have a snooze.. Sure some fishing boats turn off transmitting because they do not want the competition to see where they are or they are fishing illegally but I am sure they are monitoring the AIS for approaching vessel..

I use a stand alone NZ unit that also has a anchor watch facility that wakes me up when the anchor is dragging, that has become an essential anchoring tool.

[Dave9111]

Originally Posted by GILow

While there seems to be quite a bit of discussion around solo sailing, one question I have not found directly addressed is the issue of AIS CPA (Closest Point of Approach) and TCPA (Time to Closet Point of Approach) alarms for the solo sailor.

I would love to hear from solo sailors and others on their preferred settings for the two alarm thresholds and the logic behind their choices.

Depends on where you are sailing.

The open ocean, at night, while sleeping?
Or the Great Lakes at night while wide awake.

On Lake Erie, at night, wide awake, I have found that 1 mile CPA is the minimum. Any closer and they will scare the shxt out of you when they pop up. The freighters move fast and their lights blend in with the background making them moving shadows. The freighters are probably not the big issue because they stick with the shipping lanes, however smaller commercial boats do not always follow the shipping lanes if they don't need the draft.
I consider AIS on the Great Lakes to be a requirement at night.

[dancor01]

Originally Posted by GILow

While there seems to be quite a bit of discussion around solo sailing, one question I have not found directly addressed is the issue of AIS CPA (Closest Point of Approach) and TCPA (Time to Closet Point of Approach) alarms for the solo sailor.

I would love to hear from solo sailors and others on their preferred settings for the two alarm thresholds and the logic behind their choices.

Once in a while you will meet one of those big ship that will simply ignore you.
Rules of the road? What is that.
Trying to contact them on VHF, you get an answer that is mumbled.
Report the incident to authorities? good luck with that.

[Dave9111]

There are several places in the Great Lakes where they freighters are constrained to the shipping channels over wise they run aground.

In that situation....they can't stop in time usually and they cant change course.. This is pretty much like parking your car on a train crossing. Nothing good will come of it.

People say you should keep a look out, but on a moonless night, with lights in the background, you simply can't see many of these freighters are they approach. Everything blends into the background. Daylight is an entirely different situation. Still, sailing at night under a starry sky can be really nice. :-)

[dancor01]

Originally Posted by Dave9111

There are several places in the Great Lakes where they freighters are constrained to the shipping channels over wise they run aground.

In that situation....they can't stop in time usually and they cant change course.. This is pretty much like parking your car on a train crossing. Nothing good will come of it.

People say you should keep a look out, but on a moonless night, with lights in the background, you simply can't see many of these freighters are they approach. Everything blends into the background. Daylight is an entirely different situation. Still, sailing at night under a starry sky can be really nice. :-)

Was talking about open sea.
Not in a little pond as the so called great lakes

[Dave9111]

And the bait is in the water .... the suckers are circling..

Ha ha... how can this turn into a "Mine is bigger than yours" contest !!! :-)

[wingssail]

Originally Posted by Jim Cate

Coastal - Alarms set for 10 mile radius, CPA 2 miles, TCPA 30 min
Offshore - Alarms set for 20 mile radius, CPA 2 miles, TCPA 30 min

I'd say that it's pretty close to a consensus on this. That's about what we use.

Three points:
1. The alarm is loud. When you've been out there three days and haven't seen a ship you get lulled into complacence. That AIS alarm gets you out of it in a hurry.

2. When you are in the Malaka Straits, for example, and there are 60 vessels on your screen, the visual alarm is better than the audible, and you need a constant watch on the complete situation. (Two persons)

3. The small vessel (or bigger one) without AIS is still a danger. They don't cause an alarm at any CPA or TCPA. Good luck.

[Ammeer]

I use a Vesper Marine Watchmate 850 and have found it one of the more useful bits of kit I have on my yacht. I have done 1500 nm solo trips (even with crew we tend to operate one person on watch). I just use the Coastal, offshore settings on the AIS. I have picked up a ship 19 miles away on a direct collision course. When I called them, they had trouble reading my transmission. Their aerial was 200 m above the water, mine was 20. They called back when they could see me on AIS and radar. We were 12 miles apart at that stage. But we were both aware of each other. I could see other yachts in my race when they were 12 miles away. I found trhe effective range was about 20 miles. In 3 m breaking waves and strong winds, the sea conditions will dictate the effective distance rather than the distance you set on the alarms. The AIS might pick up other boats 20 + miles away when you are in your marina. But in the open sea, expect much shorter ranges.

[Jim Cate]

Their aerial was 200 m above the water, mine was 20.

Now THAT is a tall ship! Slight exaggeration, perhaps?

The AIS might pick up other boats 20 + miles away when you are in your marina. But in the open sea, expect much shorter ranges.

Not my experience at all, and I see no technical reason to believe your statement. Quite the contrary, in fact.

Jim

[GILow]

Originally Posted by Jim Cate

Now THAT is a tall ship! Slight exaggeration, perhaps?







Not my experience at all, and I see no technical reason to believe your statement. Quite the contrary, in fact.



Jim

Just a units problem. The same sort of thing that turned an expensive space probe into a hole on the surface of Mars.

200 FEET would be about right for a Panamax or Post Panamax ship.