VHF / Chartplotter integration for DSC (MOB)

[bedouin]

I haven't yet got round to connecting the VHF to the Chartplotter but I intend to do so primarily to allow the display of AIS information.

When I do so will I get positions from DSC alerts (e.g. MOB) displayed automatically?

I am wondering again about the PLB/AIS Beacon?HH VHF dilemma as an MOB recovery mechanism

 

[pvb]

I believe that most plotters should display DSC messages. However, I understand that not all radios will sound an alarm in response to the individual distress relay call from MOB devices, it depends on the radio. Newer radios should work OK.

Similarly, I understand that not all plotters can properly handle the AIS alert from MOB devices, and may not display an alarm message. Again, newer plotters ought to display it properly.

 

[bedouin]

These things are remarkably difficult to test - I can't really broadcast a DSC distress just to see how the chartplotter responds

 

[pvb]

These things are remarkably difficult to test - I can't really broadcast a DSC distress just to see how the chartplotter responds

Most AIS MOB devices can send a test message.

 

[[70521]]

I haven't yet got round to connecting the VHF to the Chartplotter but I intend to do so primarily to allow the display of AIS information.

When I do so will I get positions from DSC alerts (e.g. MOB) displayed automatically?

I am wondering again about the PLB/AIS Beacon?HH VHF dilemma as an MOB recovery mechanism

NO. I can't see any NMEA message sentences for converting a DSC distress CH70 message to NMEA so that it can be displayed on a chartplotter.

 

[bedouin]

Most AIS MOB devices can send a test message.

I am thinking more about the DSC side - so does a DSC HH VHF do almost as good a job as an AIS MOB.

 

[duncan99210]

I am thinking more about the DSC side - so does a DSC HH VHF do almost as good a job as an AIS MOB.

No, it does a different job. An AIS MOB transmits repeated messages with updated position fixes via the AIS system until it’s turned off. It is also automatic provided it’s been set up properly on your lifejacket.
A HH DSC VHF requires you to press a button to send a single DSC alert: not much use if you’re unable to turn the HH VHF on and press the button.

 

[bedouin]

No, it does a different job. An AIS MOB transmits repeated messages with updated position fixes via the AIS system until it’s turned off. It is also automatic provided it’s been set up properly on your lifejacket.
A HH DSC VHF requires you to press a button to send a single DSC alert: not much use if you’re unable to turn the HH VHF on and press the button.

Yes - I understand the difference.

For a piece of electronics to carry in case of MOB there is really the choice between PLB, AIS, VHF and you can't really carry all 3. When single handing the PLB is certainly the best option but when sailing quth crew it is different - then there is benefit in the MOB being able to transmit directly to the boat via VHF (either DSC or AIS).

 

[Martin_J]

The Ocean Signal Mob1 personal beacon actually sends both a DSC distress alert and an AIS man overboard alert. It should therefore show as AIS position alert on the chart plotter and as a DSC alarm sound on the radio.

As to your first question, you've not mentioned which plotter nor radio you have but our B&G Zeus plotters happily plot the location of the messages they receive from the Standard Horizon VHF radio via an NMEA0183 connection.

To test the DSC sentences before we got the Mob1s, I did some VHF position requests from the fixed VHF to the Standard Horizon handhelds. The handheld positions then appeared on the plotter in the correct positions.

 

[ShinyShoe]

Wow. For a thread on here it might have set a new record. It took 7 or 8 posts to get the right answer and the rest is mostly non-sense!

I haven't yet got round to connecting the VHF to the Chartplotter but I intend to do so primarily to allow the display of AIS information.

So start by telling us WHAT Plotter, and WHAT VHF!

When I do so will I get positions from DSC alerts (e.g. MOB) displayed automatically?

I am wondering again about the PLB/AIS Beacon?HH VHF dilemma as an MOB recovery mechanism

Tell us the models.

I believe that most plotters should display DSC messages. However, I understand that not all radios will sound an alarm in response to the individual distress relay call from MOB devices, it depends on the radio. Newer radios should work OK.

A DSC distress alert from a HH or a fixed unit will do the necessary on a DSC radio. So my understanding of the Ocean Signal MOB1 - is it will do that using DSC as a CH70 DSC alert with distress type MOB. Then continue to send AIS messages with position updates.

Similarly, I understand that not all plotters can properly handle the AIS alert from MOB devices, and may not display an alarm message. Again, newer plotters ought to display it properly.

Almost all will display something - they may not flash or scream or show a lifering. But provided the DSC has screached and so you know you need to go back and pick someone up, all you need to do is work out which target to go and get...

These things are remarkably difficult to test - I can't really broadcast a DSC distress just to see how the chartplotter responds

True. But you can using a position request to see if that position will appear on the plotter.
You can wait for a genuine DSC alert from another vessel and see it plotted (easier on the South Coast where someone will press it because they are running late for tea with Lord Montifly because the wind has dropped.
If you know the sentence sent by the radio, you can simulate it using a PC feeding the NMEA to see how the plotter handles it.

NO. I can't see any NMEA message sentences for converting a DSC distress CH70 message to NMEA so that it can be displayed on a chartplotter.

Well since this has been a thing for years to send the DSC position to a plotter - the sentence exists. Its a DSC sentence or a DSE sentence.
DSC has:
flag for –distress alert call.
the MMSI of the sender.
distress type & nature
position & time

DSE - carries more refined position data


If you program your handheld device with the MMSI which your radio / plotter knows as your boat - it is possible there will be filtering taking place to not show it.

 

[pvb]

A DSC distress alert from a HH or a fixed unit will do the necessary on a DSC radio. So my understanding of the Ocean Signal MOB1 - is it will do that using DSC as a CH70 DSC alert with distress type MOB. Then continue to send AIS messages with position updates.

Wow, talking of nonsense, have you looked at the MOB1 FAQs? The bit where it suggests which VHF radios might or might not receive an Individual Distress Relay call correctly? You'll find it here - http://oceansignal.com/products/mob1/#faqs

 

[laika]

It is a shame some posters enter a discussion with misanthropy. It seems so unnecessary.

The mob-1 apparently sends an individual call to the mmsi you program into it. It only sends an all ships distress if you hold down the on key for 5 seconds.

My old icom 603 isn't explicit about about what it sends to the plotter. It definitely sends position reports. I've never seen it plot a distress message although the plotter is supposedly capable of doing so.

This seems to be the best non-nmea reference for DSC/DSE sentences:

http://continuouswave.com/whaler/reference/DSC_Datagrams.html

I'd have thought that the plb would have been the best choice for a single handed if you could only choose one, but you can carry ais and plb. I generally sail 2 up. My partner's lifejacket has an mob-1 attached to the inflation tube of her lifejacket and a plb in a pouch on the waist strap

 

[ShinyShoe]

The mob-1 apparently sends an individual call to the mmsi you program into it. It only sends an all ships distress if you hold down the on key for 5 seconds.

They say the all ships is not allowed in UK?

Not sure how that is determined! It could be they put it in the manual. In which case if I'm feeling loanly watching my boat sail away without seeing me, I can still press it and worry about the (non) consequences later. It could be a factory mode which may or may not be user programmed. It could I guess use GPS fix. I'd want to know!

My old icom 603 isn't explicit about about what it sends to the plotter. It definitely sends position reports. I've never seen it plot a distress message although the plotter is supposedly capable of doing so.

I'd have thought that the plb would have been the best choice for a single handed if you could only choose one, but you can carry ais and plb. I generally sail 2 up. My partner's lifejacket has an mob-1 attached to the inflation tube of her lifejacket and a plb in a pouch on the waist strap

For a single hander... I'd have thought it offers very limited value! It is really intended as a "come back and get me" device. With some degree of escalation *if* you can all ships distress alert. All ships is manual. So is it any better than a epirb style plb using sats? Quicker if there is a boat local, less reliable if there isn't.

One of the country modes has a sort of cascading level of alert where if you haven't been rescued (switched off device) in a certain number of minutes it will then all ships. Sounds quite clever.

I'd want to be able to choose my mode based on my sailing! Single handed, underway. Full automatic. Single handed in harbour (the only time non dinghy sailing I've ended up in the water - stepped off the edge of a slip way. Stood up. Was only waist deep but LJ has popped). Manual. Group sailing underway, escalation sounds acceptable although I still think if I end up in the water 1mile off the shore underway things went wrong enough I'm happy to have resources sent out for me even if I'm rescued by my own crew.

 

[bedouin]

If it matters the Chart plotter in question is a Raymarine E95 and the receiving VHF radio a SH GX2200 - that can be configured to send AIS and DSC sentences via 38400 to the CP

As a rule for offshore work I think HH VHF / AIS is probably only much use to alert your own boat as you would be luck to have any other vessel within range if you are bobbing up and down on the waves - so not really much use for single handed - whereas the PLB will alert the rescue services but doesn't help your own boat find you.

 

[ShinyShoe]

If it matters the Chart plotter in question is a Raymarine E95 and the receiving VHF radio a SH GX2200 - that can be configured to send AIS and DSC sentences via 38400 to the CP

Specifically listed as compatible with distress relay.