NMEA 2000: Based on CAN, but why so flaky?

[Pyxis156]

There have been several updates to the RS35, the current firmware version is 2.87 and can be obtained from Simrad at RS35 / HS35 Software Update - Simrad Marine Electronics

Regarding a single instrument bringing down an entire network, I had a similar infuriating and intermittent problem that took a great deal of effort to figure out. Long story short, one of the my displays (Furuno in this case) mounted outside in the elements had a leak and when it rained or for a period of time after it rained and there was still moisture inside the unit, the network would literally flip out and crash repeatedly. A reboot might make things work briefly, but invariably until things dried out it would render the network unstable. Turns out that the moisture caused something in the N2K interface in the display to short and either ground or put voltage (or both) on the signal wires and since the N2K bus depends on the difference between "high" and "low" signals, effectively flooded the bus with noise and led to really bizarre intermittent behavior. It took extensive troubleshooting with a Maretron N2K Analyzer to figure this out.

I have the B&G version of this radio and the firmware update has resolved many issues and may solve this one. If it doesn't, I suggest you check the cable from the backbone to the radio to make sure that it is good. Especially if it has field applied ends, there is a chance that there is a short in the connector and that can lead to this kind of behavior. The Maretron website FAQ has some information on testing cables and what you should see when using an ohmmeter on the different pins.

Hope this helps...

[HighTemp]

Originally Posted by Pyxis156

There have been several updates to the RS35, the current firmware version is 2.87 and can be obtained from Simrad at RS35 / HS35 Software Update - Simrad Marine Electronics

Regarding a single instrument bringing down an entire network, I had a similar infuriating and intermittent problem that took a great deal of effort to figure out. Long story short, one of the my displays (Furuno in this case) mounted outside in the elements had a leak and when it rained or for a period of time after it rained and there was still moisture inside the unit, the network would literally flip out and crash repeatedly. A reboot might make things work briefly, but invariably until things dried out it would render the network unstable. Turns out that the moisture caused something in the N2K interface in the display to short and either ground or put voltage (or both) on the signal wires and since the N2K bus depends on the difference between "high" and "low" signals, effectively flooded the bus with noise and led to really bizarre intermittent behavior. It took extensive troubleshooting with a Maretron N2K Analyzer to figure this out.

I have the B&G version of this radio and the firmware update has resolved many issues and may solve this one. If it doesn't, I suggest you check the cable from the backbone to the radio to make sure that it is good. Especially if it has field applied ends, there is a chance that there is a short in the connector and that can lead to this kind of behavior. The Maretron website FAQ has some information on testing cables and what you should see when using an ohmmeter on the different pins.

Hope this helps...

Based on the symptoms and troubleshooting results, it can only be the radio or the cable itself. We will try the software update first to see if this has an effect, then the cable. If neither of them clear the issue, then the head unit has to be sent off for repair.

[alctel]

It's 100% the firmware. I had the exact same symptoms and this fixed it.

[CarinaPDX]

It sounds like the source of the problem is likely the VHF radio, so the OP should be on the way to things working.

I disagree with the initial assertion: "NMEA 2000: Based on CAN, but why so flaky?" It isn't. I have installed several networks - no problem. When there are problems it is either a rare failure of a supplier's design (this radio for instance), a failure of the installer's design (e.g. too many or not enough terminators), or an electrical fault in the devices or circuit. Pretty straightforward. We are dealing with a bus here, which by definition shares the same two signal lines with all devices and all cabling; a failure anywhere can affect the entire system.

One problem is the high cost of proprietary NMEA certification (and NMEA membership), which has discouraged manufacturers from going that route. Instead there are many NMEA "compliant" devices which have not been through the extensive official test program (and were developed without access to the proprietary specs). Another is that manufacturers insist on using their own proprietary cable designs instead of the recommended DeviceNet connections. This is a mess created by the manufacturers, both as members of NMEA and as sellers wanting to keep things proprietary. If they would just embrace an open standard and let the competitive chips fall where they may things would be so much better (for us). Personally I have just one device that uses a non-DeviceNet connector, which was the only choice at the time, and will be the last. I will also be more vigilant about certification, but in truth I have not personally encountered any N2K devices that fail to work as expected.

Another problem with N2K is the extensive use of manufacturers' proprietary sentences, and particularly for calibrating sensors. It seems that no one wants to risk sharing good ideas with competitors. Sheesh.

For most cruising boats N2K is a great solution - simple and reliable if installed correctly, even with multiple suppliers of equipment. I recognize that folks putting together 50 node systems on powerboats can encounter problems, but that is another level of complexity.

Greg