AIS CPA and TCPA for Solo Sailors

[Nicholson58]

Eyes are not so good at night especially with multiple targets. Even one target can confuse. Our Watchmate 850 antennae is 80 feet up on the main mast. We see class A up to 70 Miles. We always hail for near CPAs. I can assure you many, (most) vessels do not see you or choose to ignore. Without the AIS data it would be difficult to contact the other skipper.

On a night transit Martinique to Bequai down the east side of St Lucia and St Vincent we had four class A crossings with zero CPA. all were decided by VHS and the radio operator of the large vessel. None of them saw our low power Class B in the 20 minute or more range. In all cases we illuminated our many deck lights so they could get a visual. In one case, the AIS data indicated the vessel was constrained. Other configuration data suggested it might be a tug. We used our 50 mm night binoculars to pick out the teeny light on his tow about 1000 meters behind. It was otherwise invisible. Had we crossed behind as usual, it would have been the end. We had a pleasant exchange with the tow captain who offered to alter course and speed to let us pass ahead. He also had not noticed us. To tell the truth, we don’t sleep much in the eastern Caribbean night passages. I consider AIS crucial to night passage making and highly useful the rest of the time. It’s pretty good at finding our cruising friends in a large anchorage too.

[CapnBazza]

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.

G’day mate. I know I’m stating the bleeding obvious but there are thousands of boats out there without AIS. They don’t trigger any AIS alarm.

[GILow]

Originally Posted by CapnBazza

G’day mate. I know I’m stating the bleeding obvious but there are thousands of boats out there without AIS. They don’t trigger any AIS alarm.

Yes, very true. Not so many on the passage I am going to take though. And I will still be using the old eyeball in the usual way.

[Aguabago]

At some point you have to sleep more than cat naps. An excellent free download is http://sfbaysss.net/resource/doc/Sin...irdEdition.pdf single handed sailing tips by Andrew Evans that discusses sleep management techniques. Use radar alarms in addition to AIS alarms. Set up a sleeping arrangement (e.g. hamock) so you can open you eyes and see gauges and scan the horizon without having to fully wake up. You can always heave to to get a 90 minute nap, albeit someone can still run you over while you are hove to, so best to do that during the day.

[GILow]

Yes, there have been some great discussions here on CF about single handed sailing.

But I’m trying to keep this one focused on AIS alarms because the whole single handed thing is so contentious.

Case in point, only a couple of posts here have actually addressed the question of alarm thresholds while quiet a few are digressing into the field of what I should or should not be doing as a solo sailor.

This is why I started the thread specifically acknowledging the other discussions and identifying the AIS settings as the purpose of this discussion.

[GILow]

Originally Posted by conachair

Previous ocean was 5Nm, so anything within that would sound an alarm. Logic being I want to know! With the Rasp Pi now linked up to speakers hopefully the watchdog plug will do something a little cleverer so I don't have to wait for the ship to pass 5Nm away before snoozing again.



Coastal no alarms set, only very short cat naps if anything so know whats out there already.

Sorry conachair, missed your valuable contribution. Good point about alarm behaviour for us to consider. Ok, the alarm wakes us up, we decide the identified vessel is no threat, how do we clear the alarm and what is the system behaviour of the vessel subsequently alters course in a way that makes it more of a threat? Case in point, I’ll be travelling through a lobster field and those boats can move in very unpredictable ways.

[roland stockham]

I have used AIS quite a bit both solo and 2 handed. Not found the CPA alarm very useful. The way I use it is to alert me to the presence of ANY shipping in the vacinity. I usually have it set at 30m offshore but reduce the distance to 15m approaching coastal areas. If there is nothing visable on AIS I am happy to sleep withe ste radar guard set (looking out for non AIS vessels such as other Yachts). If there is anything on the screen I am on watch athough I may catnap. I can go 2 or 3 days like this but then need a full 8hr. The balance has to be knowing when a full watch is essential butnot getting so tired you start making serious mistakes.

[JPA Cate]

GILow,

It would help to know your possible itinerary for the voyage you are contemplating. Will you be going straight through to somewhere? Will there be any opportunities for a good sleep before entering more crowded waters? I realize this is a kind of hijack into voyage planning, but what you have and how you use it may also be to some extent on your area.

I would think you'd like warning of ships at 20 miles, and accepting that sometimes their AIS goes down--heard one bound for Pt. Kembla announcing to the Harbor Control that his was not functioning. Finding a solution to receiving notification of non-AIS equipped sail or power boats at about 10 miles would be a good idea. Most sailboats are not visible very far off on radar--about average @ 2 n. mi. And radar takes a lot of power to run, so what do you do about them?

Ann

[GILow]

Hey Ann, my question was general in nature, but yes, prompted by a planned trip. I've got a six or seven day passage from Adelaide to Hobart coming up, early November in all probability. The journey can be done as a series of coastal hops or as a single straight shot from Kangaroo Island. As per advice from many on this forum, yourself included, I am going to try avoiding the coastal day hops and go direct. Problem is, two or three days of the journey will be parallel with a moderately busy shipping lane (see picture attached) and at one point I will need to cross a moderately busy shipping lane. (I say moderately busy, of course by the standards of say, the English Channel, these shipping lanes are ghost towns) Oh, and the first day or two are through a lobster pot field, just for good measure.

In reference to sleep, plan is to head for Kangaroo Island, get well rested at American River while watching the weather. Then head out. The Tasmania end is easier, I'll just pull into any of the myriad of sheltered waterways and snooze a day or two before heading around to Hobart. The reverse journey would be similar, pulling in to American River to sleep before heading back to Adelaide.

[JPA Cate]

Hi, Matt,

Mmmm. Might be better to cross the traffic zones perpendicular to them, catching the northern one just out of K. Island. You give up ground, but get across faster, thus limiting your exposure. The airs of the D'Entrecasteaux Channel are often light and flukey, and where you will encounter the higher concentrations of yachties.

Depending on the wind directions there are rolly anchorages available around the Cox's bight area, if you're way tired. [Rolly anchorages usually not a problem after a few days at sea.] Also, if exhausted, you could duck into Pt. Davey. A shame to miss it. Nice place to take off from on your way back to Adelaide, too.

Our experience on approaching Tassie is that there are an unknown to me number of timber, unlit, cray boats around, possibly poachers, w/o some way of seeing them, they are a concern. We only encountered one. I guess you have in mind a Hobart rdv with a GGR participant. Maybe radar with a 2 n. mi. alarm zone might help, the problem is that timber does not offer good radar returns. Once rested, you should, for instance, be able to sail from Recherche Bay around the S side of Bruny Is. to Hobart inside of one 24 hr. period.... I just took a look at a route outside everything from Pt. Davey to Hobart: 119 n. mi. Opportunities for cat naps on the outside.

Have a great trip, Matt.

Ann

[GILow]

Originally Posted by JPA Cate

Hi, Matt,

Mmmm. Might be better to cross the traffic zones perpendicular to them, catching the northern one just out of K. Island. You give up ground, but get across faster, thus limiting your exposure. The airs of the D'Entrecasteaux Channel are often light and flukey, and where you will encounter the higher concentrations of yachties.

Depending on the wind directions there are rolly anchorages available around the Cox's bight area, if you're way tired. [Rolly anchorages usually not a problem after a few days at sea.] Also, if exhausted, you could duck into Pt. Davey. A shame to miss it. Nice place to take off from on your way back to Adelaide, too.

Our experience on approaching Tassie is that there are an unknown to me number of timber, unlit, cray boats around, possibly poachers, w/o some way of seeing them, they are a concern. We only encountered one. I guess you have in mind a Hobart rdv with a GGR participant. Maybe radar with a 2 n. mi. alarm zone might help, the problem is that timber does not offer good radar returns. Once rested, you should, for instance, be able to sail from Recherche Bay around the S side of Bruny Is. to Hobart inside of one 24 hr. period.... I just took a look at a route outside everything from Pt. Davey to Hobart: 119 n. mi. Opportunities for cat naps on the outside.

Have a great trip, Matt.

Ann

Thanks Ann, yes, definitely plan to cross that major shipping channel at a sharper angle, that red line is not exact. Thanks for the tips about possible anchorages. I have a fall back option of Port Macquarie too (with due regard to the difficulties of getting in there), if I think I am needing a rest.

Yes, plan to be there to cheer on Mark Sinclair on Coconut, he mentioned the 15th of November on his satellite call last night, so that gives me something to aim for, though I reckon he might get there sooner. Plan to arrive at least a week before him so plenty of time to play with weather and rest if needed.

My last 500 mile journey was done against the clock, not falling for THAT trap again.

[Jim Cate]

Matt, specific answer to your questions:

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

This of course is for us, where we do have someone on watch 24/7. But seems like reasonable settings for solo and napping as well.

You will likely be able to receive AIS from ships at well over 20 miles. We routinely see them at 35-50 miles, and of course under extraordinary conditions, over 1000 miles. This sort of range helps when contemplating crossing a traffic lane, and allows some long range planning. I think you will find, as we have, that once you are transmitting AIS ships will maneuver to avoid close CPAs long before they heave over the horizon. I know that some folks here on CF don't believe that, but that's our experience, especially when sailing coastal Australia. I suppose that the crew on ships that ply these waters know that there is a lot of small craft traffic and are paying more attention than they do offshore.

Looking forward to sharing some anchorages with you and Manera.

Jim

[Wotname]

Originally Posted by GILow

....... Oh, and the first day or two are through a lobster pot field, just for good measure.

..........

Continuing with the unsolicited extraneous and probably unneeded off topic advice ...

I dunno the exact underwater shape of your Sannie but I hope you have your prop / rudder protected from snagging the cray lines!!! I hate those buldi lines, hard to see at night but when you catch one, it's never good.


Some (many?) decades back, we were broad reaching in 25+ kts of onshore wind up the WA coast and snagged 3 lines in one night. Each time going from hull speed to barely one knot nicely anchored by a cray line around the rudder. The boat immediately faced DDW with a decent sized sea state breaking over the stern half filling the cockpit (Giles 28' Wanderer). The rudder pintles taking all the load! Not fun but we lived! Of course, the solution was simple, we should have moved another ten miles further offshore to be off the continental shelf and be away from the cray lines (and get a better sea state at the same time) but we weren't smart enough.

[GILow]

Originally Posted by Wotname

Continuing with the unsolicited extraneous and probably unneeded off topic advice ...

I dunno the exact underwater shape of your Sannie but I hope you have your prop / rudder protected from snagging the cray lines!!!

How's this?

[GILow]

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

This of course is for us, where we do have someone on watch 24/7. But seems like reasonable settings for solo and napping as well.

Thank you Jim. A different mix of numbers again to those previously suggested. And from one of the faster boats in the fleet on CF.

Interesting to try to interpret that if I can. Will think some more.