AIS transponder. Now you need it?

[BrianH]

And the alarm mechanism is not much use; where I am it gets set off by large commercial vessels moored in the dock, so I tend to ignore the alarm!

OpenCPN allows a no alarm condition for static ships - seems a basic functionality requirement to me. I found it as I regularly sail past an anchorage for small freighters waiting to enter Porto Negaro in Italy and got fed up with the close CPA alarms they generated. A check of the preferences soon found how to turn them off.

 

[davidej]

The only CG station fitted with radar is Dover for the Channel TSS.

Are you sure this is right.

I thought the large mast at Walton-on-the-Naze is radar for the CG monitoring shipping in the Haven Ports/ Sunk TSS area.

 

[Conachair]

But if the ship's head may be at either end of the vessel, it can easily be 180 degrees out. The basic "Quick look" display simply shows ships head, NOT COG etc; these are buried deeper in the display information and although they may be more reliable they are not part of the information available at a glance, at least, not on my chart-plotter.

Doesn't sound ideal. Just checked my nasa, it shows MMSI, name, range, lat & long, status , heading, SOG and COG . Quite often the heading will read 511deg which I believe means no heading sensor attached. Also sometimes the status will read anchored when obviously not.

Just checked half a dozen boats going up and down the thames, all show heading as 511deg.

But then again there is no other way of knowing a boats heading, short of asking on vhf. Lat, long SOG & COG are where it's at.

http://www.marinetraffic.com missing most boats on the thames today

 

[Duffer]

I turned on my electronics yesterday in a Plymouth marina and there were 3 boats transmitting AIS. All said they were underway using engine. All were doing 0.0 knots. If you leave your boat to go home please remember to turn off your AIS transmitter!

 

[BrianH]

I turned on my electronics yesterday in a Plymouth marina and there were 3 boats transmitting AIS. All said they were underway using engine. All were doing 0.0 knots. If you leave your boat to go home please remember to turn off your AIS transmitter!

Your implication is that these were yachts in a marina and presumably Class B transponders that were left switched on.

However, a Class B transponder does not transmit any Navigational Status report data, which is what you are displaying with "underway using engine". Therefore, it may be that your receive/display device - plotter or whatever, is not decoding a Class B signal correctly.

On the other hand, perhaps the boats are mega yachts or rich owners that have installed Class A transponders - as many do to overcome the minor disadvantages of the Class B units. Unless, of course, some fast-talking salesman had convinced them that they are not so minor.

 

[RobbieW]

But if the ship's head may be at either end of the vessel, it can easily be 180 degrees out. The basic "Quick look" display simply shows ships head, NOT COG etc; these are buried deeper in the display information and although they may be more reliable they are not part of the information available at a glance, at least, not on my chart-plotter.

Can you set your plotter to show, as OpenCPN puts it, a target 'COG predictor arrow'? iirc Raymarine plotters have the function but I cant remember what its called. The length of the arrow is determined by the SOG of the target. If the target arrows are set to the same length of time as the own boat predictor arrow you get a good quick visual on likely problem situations.

Again iirc, some of the setup for an AIS unit includes the position of the sensors. This probably gives an indication of the ships orientation which helps explain those seeming to go backwards.

 

[Twister_Ken]

Does anyone know who looks at the scanner that's sited "under" the Orwell bridge on the south bank?

I'd suggest the local VTS.

Or the Highway Authority

 

[Lucky Duck]

I'd suggest the local VTS.

Or the Highway Authority

Most likely it will be the Ipswich Port Authority, there is a similar radar located at the top of the marina office of Suffolk Yacht Harbour further downstream at Levington.

 

[AntarcticPilot]

OpenCPN allows a no alarm condition for static ships - seems a basic functionality requirement to me. I found it as I regularly sail past an anchorage for small freighters waiting to enter Porto Negaro in Italy and got fed up with the close CPA alarms they generated. A check of the preferences soon found how to turn them off.

I would agree, except that how does OpenCPN tell that a ship is static? I'm afraid that the speed indication can tell lies as well!

 

[AntarcticPilot]

Can you set your plotter to show, as OpenCPN puts it, a target 'COG predictor arrow'? iirc Raymarine plotters have the function but I cant remember what its called. The length of the arrow is determined by the SOG of the target. If the target arrows are set to the same length of time as the own boat predictor arrow you get a good quick visual on likely problem situations.

Again iirc, some of the setup for an AIS unit includes the position of the sensors. This probably gives an indication of the ships orientation which helps explain those seeming to go backwards.

I may well be able to do so. But the obvious indicator is the big grey wedge, and that is set by the ship's head. As I mentioned, my chart-plotter is not in the cockpit - it doesn't make much sense for a boat steered by tiller - so an indication I can't see at a distance of several feet isn't much use to me.

 

[maxi77]

I've never bought AIS and never would, they seem a waste of money to me. I've got four Mark 1 eyeballs on board and radar that we only turn on in fog. I'm probably in the minority with that view but it works for me

We have the same and I was tought collision avoidance profesionally, but I do find AIS useful and would always prefer to have it on any boat I sailed. In exactly the same way I would prefer to have radar, though I was equally trained to do it without radar too. Equally I think radar with mini arpa is more useful than radar without it. They are all tools you can use to make life easier, safer, and more enjoyable.

 

[BrianH]

I would agree, except that how does OpenCPN tell that a ship is static? I'm afraid that the speed indication can tell lies as well!

From the Help manual is is fairly clear that the "Navigation Status" is used, that is, when it reads "Anchored" or Moored". I personally think that a speed of zero may be more accurate as it is almost certainly from the GPS calculation and automatically transmitted, rather than manually input.

As the manual says, "There is no guarantee that this status is correct, as it is set manually on the transmitting ship..."

However, in my own experience, commercial shipping seem very consistent in setting "Anchored" and "Moored" but less so in cancelling it when underway. Nevertheless, in all events it is better than nothing and certainly effective in my area.

Edit 1: An after thought; presumably a non-zero SOG probably overrides the CPA alarm OFF setting - if not then it should do.
Edit 2: Belay Edit 1. Just found in Toolbox>AIS the possibility to modify "max moored target speed (kts) [ ] CPA TCPA". So this would appear (to me) to initiate a warning even if the alarm inhibition is set for anchored ships. There is quite a long thread partly on this subject from the developers here.

 

[BrianH]

We have the same and I was tought collision avoidance profesionally, but I do find AIS useful and would always prefer to have it on any boat I sailed. In exactly the same way I would prefer to have radar, though I was equally trained to do it without radar too. Equally I think radar with mini arpa is more useful than radar without it. They are all tools you can use to make life easier, safer, and more enjoyable.

I agree that radar would be a very nice thing to have but completely impracticable on cost and Amps for a small sailing boat.

In comparison, an AIS receiver is cheap and runs on milliamps - no contest.

It also can calculate CPAs around headlands, promontories and islands where the topography would block the higher frequency radar returns. I'm not saying that it replaces radar, rather complements it, but when one compares the bang for the buck, I'll stick to AIS.