Sea Talk NG Intermittent fault

superheat6k

superheat6k

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A friends boat has an annoying issue with the Seatalk NG comms or one of the attached instruments. Here are the symptoms so if anyone has seen this perhaps they could offer their experience ...

Instruments on the Seatalk NG System ...

Raymarine Type 100 Course computer
Autohelm ST7000 Autohelm unit
Garmin GMI20 multi function display for Depth, Heading. Speed, Log
Repeater Garmin same on Flybridge
- these were recently renewed due to faded screens, which is when the comms problem began
VDO Compass
Depth via the Garmin
Log via the Garmin
VHF Raymarine
Raymarine C120 plotter picking up the above data for position

Problem

The system is powered on and within a few seconds all data is displayed on all instruments correctly
Then after ~ 5 minutes the comms brakes down and displays 'No Link' on the ST7000
The ST7000 auto helm no longer functions at all
The position is lost to the VHF
The Garmin multi repeaters lose heading data
The Compass freezes
Depth and log remain available on the Garmin displays

A power off reset resolves the problem for the next 5 minutes.

We have checked all connections to the Type 100 computer.

Has anyone seen an intermittent cut out like this and if so what was the root cause.
 
Last edited:
I’m no expert I’m afraid but is it possible that there is too much power draw on the N2K (SeatalkNG) network? I’ve seen one or two posts on here recently where there has been talk of adding an extra 12v power feed to an overburdened N2K network.
 
fredrussell said:
I’m no expert I’m afraid but is it possible that there is too much power draw on the N2K (SeatalkNG) network? I’ve seen one or two posts on here recently where there has been talk of adding an extra 12v power feed to an overburdened N2K network.
Click to expand...
Hadn't considered that. When the Garmin multi displays were added the work included a new backbone, so possibly too much equipment. I will look into how to introduce a second power injection.
 
Break down the network into two halves. Buy an extra pair of terminators if you like, or just move the bow terminator half way up the boat and leave the front half of the SeatTalkNG backbone disconnected. Does the fault still occur? No, then the cause is one of the instruments or connections in the part of the network that you disconnected.

Or start with a minimal network, with just the ST7000 and one other device - does the fault still occur?

But wait! The ST7000 is ancient, and there's no mention of SeaTalkNG in its manual - it cannot possibly be on the SeatTalkNG network (??), and must be getting SeaTalk1 data from another Raymarine device.

If the problem occurred only since a Garmin device was replaced then try unplugging the Garmin devices - all at once and then one at a time - to see fi the problem goes away. If they're on a SeaTalkNG / NMEA 2000 network then I think you can just disconnect the cable that's connected to them.

I'm assuming the owner did not mess with the SeaTalkNG / NMEA 2000 network when he replaced the Garmin(s)? The network should have a "backbone" which runs (figuratively) from the boat's bow to stern, as explained / pictured here.
 
The new Garmins and STNG / N2K backbone were all installed by a professional marine electronics firm, who have now washed their hands of the matter.

So upon reading more I am wondering if the problem here is that the older Sea Talk 1 ST7000 would talk fine with other Raymarine devices which can also talk on STNG and the associated N2K backbone network recently fitted by the professional installer, but the ST7000 will not talk to the Garmin properly without a Sea Talk 1 to Sea Talk TNG convertor.

Feedback on whether this might resolve the issue most appreciated.

Now where to source a ST 1 to STNG convertor.

However, there has now developed quite a row between the boat owner who I am trying to assist and his professional installer. So if the installer failed to recognise the need for a ST1 to STNG convertor then the boat owner, who is not by any means a marine electronics expert, has a fair claim against the installer that he has failed to properly re-assign the comms network. It is after all loss of comms to the ST7000 that is the root of the problem here. The owner does not want a row, he simply wants his system to work.
 
Any legacy ST1 devices should be connected together as normal, then connected to a ST1 to STNG converter.

Suggestions of adding a second power source are incorrect, there should only be a single power source. If it is a power issue, there are special tee connectors available that allow two power connection, one supplies power to the left of the connector, the other supplies power to the right of the connector.
 
This may not be relevant, but faulty equipment can cause very odd symptoms on a Seatalk network. My Raymarine tiller pilot went bad, and the immediate (and non-obvious!) symptom was that the log suddenly switched to displaying in kilometres per hour instead of knots. There were other, less obvious things happening, too. Disconnecting the tiller-pilot fixed the issues in the rest of the network. I have no idea why that should happen, but it did and was VERY confusing until we realised the tiller-pilot had stopped working - it wasn't immediately obvious as we were under motor and the tiller-pilot simply froze in a centred position. Investigation showed that the tiller-pilot had got water damage inside, the common way that Raymarine tiller-pilots fail.
 
As @PaulRainbow says, the STNG backbone should only have one power source.

I would definitely check that the power supply and power source are healthy, low voltage could definitely cause equipment to become temperamental.

Make sure you are checking the voltage at the point where it enters the STNG backbone, and with all other loads that you would typically have running when underway powered up (lights, fridge etc). Even if the power source (batteries) are good, you could have a poor connection or incorrectly sized cable somewhere upstream causing a voltage drop along the way.

Lastly, if the power enters the backbone at one end, you could try moving it to a central point on the backbone so that the distance it has to supply either way is reduced. However in reality, this only tends to be necessary on very large systems.
 
superheat6k said:
A friends boat has an annoying issue with the Seatalk NG comms or one of the attached instruments. Here are the symptoms so if anyone has seen this perhaps they could offer their experience ...

Instruments on the Seatalk NG System ...

Raymarine Type 100 Course computer
Autohelm ST7000 Autohelm unit
Garmin GMI20 multi function display for Depth, Heading. Speed, Log
Repeater Garmin same on Flybridge
- these were recently renewed due to faded screens, which is when the comms problem began
VDO Compass
Depth via the Garmin
Log via the Garmin
VHF Raymarine
Raymarine C120 plotter picking up the above data for position

Problem

The system is powered on and within a few seconds all data is displayed on all instruments correctly
Then after ~ 5 minutes the comms brakes down and displays 'No Link' on the ST7000
The ST7000 auto helm no longer functions at all
The position is lost to the VHF
The Garmin multi repeaters lose heading data
The Compass freezes
Depth and log remain available on the Garmin displays

A power off reset resolves the problem for the next 5 minutes.

We have checked all connections to the Type 100 computer.

Has anyone seen an intermittent cut out like this and if so what was the root cause.
Click to expand...
Where does GPS info come from?
I had similar issues as this and they problem turned out to be a conflict between GPS info. The AIS had it own GPS and the raymarine plotter had its own GPS. I could choose the raymarine GPS but the plotter still received GPS info from the AIS. It produced spurious faults stoping the autopilot working properly.
 
geem said:
Where does GPS info come from?
I had similar issues as this and they problem turned out to be a conflict between GPS info. The AIS had it own GPS and the raymarine plotter had its own GPS. I could choose the raymarine GPS but the plotter still received GPS info from the AIS. It produced spurious faults stoping the autopilot working properly.
Click to expand...
I just avoided that potential issue solved as per Mr Rainbow on another current thread - GPS antenna question ?
 
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