I hear it said all the time that N2K is "easy" and it is much easier than the older 0183 standard but damage can still be done by not following the instructions.
I was recently called to a vessel for some NMEA 2000 (N2K) issues. I did not do the install and they owner apparently did it with the "help" of someone else. Really not much help as you'll see.. An N2K system is NOT Lego's! Just because a terminal fits somewhere does NOT make it the correct topography for the system..
The first step in any N2K issues is always a survey of the existing devices that should show up, GPS antenna, rate compass / heading sensor, sounder, speed, temp, radar, wind, all instruments, AP, plotter/plotters etc.. I dug into the vessel and found two plotters, radome, wind, speed/temp/depth (DST-800), Auto Pilot, GPS antenna, rate compass/heading sensor and instruments.
Complaints: No sea water temp, no wind, no heading sensor, radar turning on and off and no data repeated on the plotters.
Bottom line: The N2K bus was a MESS and installed completely incorrectly! There are four main parts to an N2K bus.
1) Back Bone - This runs throughout the vessel and allows instruments and power drops to be fed into the system via the drop port of a Tee. The back bone must have terminators (resistors) at each end.
2) Drop Ports - Devices such as plotters, instruments, heading sensors, depth/speed/temp etc. are intended to come into the system via the drop port on the back bone tee's, or a 4 port expanded etc.. These types of devices are intended to plug into the drop port NOT the back bone side of the tee..
3) Terminators - You can not leave an open port on the back bone and MUST be very careful with certain devices such as wind that may act as a terminator not to plug it into a drop port but rather into the back bone. No back bone terminator, no work. Plug in a wind that acts as a "terminator" to a "drop port" and you just created issue. Wire up a wind instrument that does not have a resistor, and fail to install an "in-line" resistor, and you once again create problems.
4) Power - Power can be fed into the system in two ways. You can use a back bone "power tee" which is inserted into the back bone or via a "power drop" which is inserted into a drop port.. The two are different and you need to know which type you are using.
What I Found:
*Wind instrument which is a "terminator device" plugged into a "drop port" = BAD!
*Power drop fed into the back bone = Incorrect For this brand/system the power feed comes into the drop ports. Some N2K systems use a "power tee". The two wire into the system differently and the NMEA standard allows for this it is up to you to read the instructions for the products you have.. A "power tee" is inserted into the back bone but a power drop is inserted into the drop port.
*Tee drop ports used as back bone and back bone ports used as drop ports..
*Multiple 18" N2K drop cables interconnecting tee's with devices plugged into any old port. It was NOT set up as a back bone with drops but rather a spider web with $hit plugged in where ever it would fit/mate to...
*Power drop near mast base was using vessels "bonding system" as DC negative. The green bonding wire was terminated within a few inches of the starter motor. This could have induced voltage transients into the N2K bus as well as led to DC corrosion on the bonding system, which is NOT designed to carry any current.
* Instruments were "drop daisy chained" like older ST-60's but not dropped back into the back bone. This can work but drop daisy chaining is advised against. Each instrument should have its own drop into the back bone or the instruments are inserted into the back bone and become part of the back bone path....
*Plotter feeding one end of back bone not into a drop port and not a terminator..
The list goes on and on... In short I had to add 5 tees and one terminator to the system as well as install multiple new drop cables.
Once the system was wired correctly I reset the system and did an auto search for connected devices. With wind plugged into the system it killed the entire N2K bus and only the plotter was visible. Unfortunately it took connecting and disconnecting every device in order to figure out which one was causing the bus issue. With wind out of the system I was able to see most devices. The speed/depth temp failed to show temp which meant an internal failure of the DST-800's temp circuit. Wind was dead and causing system issues, and the heading sensor was also not showing up & dead.. All in all, considering the poor installation and complete disregard for the instructions, he is lucky to only need to replace about $1800.00 worth of equipment..
Please, please, please read the instructions or hire or consult a qualified tech. Through a long conversation with tech support it was determined that the original configuration led to the demise of wind, heading sensor and the temp circuit of the DST-800.
Easy? Yes and no, especially if you ignore the installation manual.....
I was recently called to a vessel for some NMEA 2000 (N2K) issues. I did not do the install and they owner apparently did it with the "help" of someone else. Really not much help as you'll see.. An N2K system is NOT Lego's! Just because a terminal fits somewhere does NOT make it the correct topography for the system..
The first step in any N2K issues is always a survey of the existing devices that should show up, GPS antenna, rate compass / heading sensor, sounder, speed, temp, radar, wind, all instruments, AP, plotter/plotters etc.. I dug into the vessel and found two plotters, radome, wind, speed/temp/depth (DST-800), Auto Pilot, GPS antenna, rate compass/heading sensor and instruments.
Complaints: No sea water temp, no wind, no heading sensor, radar turning on and off and no data repeated on the plotters.
Bottom line: The N2K bus was a MESS and installed completely incorrectly! There are four main parts to an N2K bus.
1) Back Bone - This runs throughout the vessel and allows instruments and power drops to be fed into the system via the drop port of a Tee. The back bone must have terminators (resistors) at each end.
2) Drop Ports - Devices such as plotters, instruments, heading sensors, depth/speed/temp etc. are intended to come into the system via the drop port on the back bone tee's, or a 4 port expanded etc.. These types of devices are intended to plug into the drop port NOT the back bone side of the tee..
3) Terminators - You can not leave an open port on the back bone and MUST be very careful with certain devices such as wind that may act as a terminator not to plug it into a drop port but rather into the back bone. No back bone terminator, no work. Plug in a wind that acts as a "terminator" to a "drop port" and you just created issue. Wire up a wind instrument that does not have a resistor, and fail to install an "in-line" resistor, and you once again create problems.
4) Power - Power can be fed into the system in two ways. You can use a back bone "power tee" which is inserted into the back bone or via a "power drop" which is inserted into a drop port.. The two are different and you need to know which type you are using.
What I Found:
*Wind instrument which is a "terminator device" plugged into a "drop port" = BAD!
*Power drop fed into the back bone = Incorrect For this brand/system the power feed comes into the drop ports. Some N2K systems use a "power tee". The two wire into the system differently and the NMEA standard allows for this it is up to you to read the instructions for the products you have.. A "power tee" is inserted into the back bone but a power drop is inserted into the drop port.
*Tee drop ports used as back bone and back bone ports used as drop ports..
*Multiple 18" N2K drop cables interconnecting tee's with devices plugged into any old port. It was NOT set up as a back bone with drops but rather a spider web with $hit plugged in where ever it would fit/mate to...
*Power drop near mast base was using vessels "bonding system" as DC negative. The green bonding wire was terminated within a few inches of the starter motor. This could have induced voltage transients into the N2K bus as well as led to DC corrosion on the bonding system, which is NOT designed to carry any current.
* Instruments were "drop daisy chained" like older ST-60's but not dropped back into the back bone. This can work but drop daisy chaining is advised against. Each instrument should have its own drop into the back bone or the instruments are inserted into the back bone and become part of the back bone path....
*Plotter feeding one end of back bone not into a drop port and not a terminator..
The list goes on and on... In short I had to add 5 tees and one terminator to the system as well as install multiple new drop cables.
Once the system was wired correctly I reset the system and did an auto search for connected devices. With wind plugged into the system it killed the entire N2K bus and only the plotter was visible. Unfortunately it took connecting and disconnecting every device in order to figure out which one was causing the bus issue. With wind out of the system I was able to see most devices. The speed/depth temp failed to show temp which meant an internal failure of the DST-800's temp circuit. Wind was dead and causing system issues, and the heading sensor was also not showing up & dead.. All in all, considering the poor installation and complete disregard for the instructions, he is lucky to only need to replace about $1800.00 worth of equipment..
Please, please, please read the instructions or hire or consult a qualified tech. Through a long conversation with tech support it was determined that the original configuration led to the demise of wind, heading sensor and the temp circuit of the DST-800.
Easy? Yes and no, especially if you ignore the installation manual.....
