Collision Warnings

[nfbr]

Do any of the Radar / AIS systems combine these inputs, and vector to provide collision alerts?
I have seen some based on AIS and static position, but nothing with radar for non AIS vessels
I'm not clear on the vector mapping if they work out future collision probability.

I'm thinking for watch at night as another set of eyes

And possibly for security if they track anything moving toward you.

Thanks
Paul

[smac999]

Ais will alarm if other ais boats get close. Radar should do if you have arpa.

[donradcliffe]

AIS will alarm if you set the alarm parameters. However, you may want to set the parameters differently if you are in New York harbor instead of 200 miles offshore.

[Paul L]

If your radar has a quality ARPA feature then you can setup various warning and tracking of targets. It requires a stable compass heading to function well. We use the features on our Furuno chartplotter/radar often.

[mlydon]

My raymari e7 did great in combination with the heading sensor from my evo autopilot and a dish. You can set 'guard' zones all the way around, or a forward wedge, and set inner and outer limits.

Matt

[nfbr]

Originally Posted by mlydon

My raymari e7 did great in combination with the heading sensor from my evo autopilot and a dish. You can set 'guard' zones all the way around, or a forward wedge, and set inner and outer limits.

Matt

Did it do this based on other vessels projected track / vector?

Thanks
Paul

[Dockhead]

Among recreational radars, only Furuno has actual ARPA. The others have MARPA which does not automatically acquire targets.


But that doesn't matter. The way most people do it is like this:


1. Set AIS alarm to parameters appropriate to the sea area. If you are far offshore, 2 miles CPA, 1 hours TCPA might be good. Offshore but where there is traffic, maybe 1 mile CPA, 30 minutes TCPA. In denser traffic, less. In harbour areas or approaches to harbours, turn it off.


2. Set radar guard zones appropriate to where you are. Offshore, I like to set two of them -- a circular one 1 mile out, and a sector 2 or 3 miles out forward. Obviously this will not be useful if there are a lot of targets -- like channel markers -- but is very useful indeed offshore. Turn it off in harbours or approaches to harbours.



The guard zone will not give you a really comfortably timely warning for risk of collision situations with vessels not transmitting AIS, but might give you a sort of adequate last minute warning, in case you missed whatever it was.


Obviously this is not a substitute for keeping a good watch!! But these alarms can be extremely valuable to help catch something you do miss -- as an enhancement to a good watch.

[Dockhead]

Originally Posted by nfbr

Did it do this based on other vessels projected track / vector?

Thanks
Paul

Radar guard zones simply sound an alarm if an object appears in the zone you set.


An ARPA alarm will sound if the projected track of the other vessel results in CPA/TCPA less than the parameters you set -- like AIS alarm does.



But recreational radars except Furuno don't have ARPA.

[CatNewBee]

Can someone enlighten me what actually MARPA stands for?

[Paul L]

Originally Posted by CatNewBee

Can someone enlighten me what actually MARPA stands for?

automatic radar plotting aid (ARPA)
The M is mini for a reduced feature set, as defined by the vendor

[Q Xopa]

Originally Posted by Dockhead

Radar guard zones simply sound an alarm if an object appears in the zone you set.


An ARPA alarm will sound if the projected track of the other vessel results in CPA/TCPA less than the parameters you set -- like AIS alarm does.



But recreational radars except Furuno don't have ARPA.

The Halo24's, B&G etc have MARPA

[Dockhead]

Originally Posted by CatNewBee

Can someone enlighten me what actually MARPA stands for?

Mini Automatic Radar Plotting Aid


"Mini", as someone else said, means reduced features. But practically it's just automatic acquisition of targets.


But without automatic acquisition of targets, you can't have alarms that alert you to targets you didn't see already and acquire into the system.


But that would be useless on most recreational radars anyway -- the bearing discrimination is too poor and the calculations of COG and SOG of the target are too erratic.


Somehow Furuno seem to have a secret which other makers don't know, because by all accounts Furuno radars do ARPA competently.


MARPA on my B&G 4G radar is a joke; pretty much useless. Worse than MARPA on my old steam-powered Raytheon Pathfinder 24" dome.



So I use more traditional methods of radar plotting -- either do a full paper radar plot, or just set ELB/VRM on the target and observe whether the target is getting closer (by comparing to the VRM) and whether the bearing is changing (by comparing to the ELB).



This works fantastically well, so I don't find myself missing ARPA all that much. What is great about the ELB/VRM method is that it works even with very poor bearing discrimination -- that is, even with a really crappy radar. Because the TREND is visible; the outliers are averaged out.


If there is a risk of collision, the target "walks" down the ELB -- it is strikingly obvious. This is a fantastic tool, much more important than MARPA/ARPA, and actually perfectly adequate for dealing with one or two non-AIS transmitting targets at a time.


If you want to know CPA/TCPA for a non-AIS transmitting target, and you don't trust your MARPA, then you have to do a full paper plot. I do this from time to time, but rarely. I don't encounter all that many targets of concern which are not transmitting AIS, and when I do, the ELB/VRM is generally enough -- you just maneuver until there is clearly no collision risk -- you can see it.

[Dockhead]

Originally Posted by Q Xopa

The Halo24's, B&G etc have MARPA

All recreational radars have at least MARPA, AFAIK. Whether or not it works well enough to be useful is another question.

[kokajambo]

Originally Posted by Dockhead

Mini Automatic Radar Plotting Aid
...
But that would be useless on most recreational radars anyway -- the bearing discrimination is too poor and the calculations of COG and SOG of the target are too erratic.
...
MARPA on my B&G 4G radar is a joke; pretty much useless. Worse than MARPA on my old steam-powered Raytheon Pathfinder 24" dome.
...

Do you have a compass that feeds heading data to your radar and/or plotter?

[Dockhead]

Originally Posted by kokajambo

Do you have a compass that feeds heading data to your radar and/or plotter?

Of course. Otherwise many radar functions would not work.


I have a very good compass, too -- an Airmar H2183, which was the best non-satellite compass you could buy when I did my electronics.



I am thinking about buying my boat a present and upgrading this to a satellite compass, but I don't think this will help MARPA on my radar so much. I think for that I need a different radar -- one with better bearing discrimination, if I want MARPA to work well, and maybe something with better software than my B&G/Navico.