NMEA 2000

[Norman_E]

I am going to install an NMEA 2000 instrument system to replace the VDO Logic instruments on my boat. So far I have bought a Garmin GMI 10 instrument and a Garmin NMEA2000 GPS on E-bay for much less than list prices, and am about to buy a starter kit consisting of a further instrument, a hull transducer and a masthead wind unit plus all the cables required. (probably B&G Triton rather than Garmin)

My big issue is that the existing MHU has a cable consisting of at least 7 cores up the mast. It will be very hard to pull it out and get the new 5 core NMEA2000 cable in its place. Does anyone know if I can just cut off the existing cable connector at the masthead and put on NMEA2000 field installable connectors at both ends of the existing cable? I think that NMEA2000 cable has shielded pairs whereas the existing cable does not as far as I can tell.

 

[David2452]

I am going to install an NMEA 2000 instrument system to replace the VDO Logic instruments on my boat. So far I have bought a Garmin GMI 10 instrument and a Garmin NMEA2000 GPS on E-bay for much less than list prices, and am about to buy a starter kit consisting of a further instrument, a hull traducer and a masthead wind unit plus all the cables required. (probably B&G Triton rather than Garmin)

My big issue is that the existing MHU has a cable consisting of at least 7 cores up the mast. It will be very hard to pull it out and get the new 5 core NMEA2000 cable in its place. Does anyone know if I can just cut off the existing cable connector at the masthead and put on NMEA2000 field installable connectors at both ends of the existing cable? I think that NMEA2000 cable has shielded pairs whereas the existing cable does not as far as I can tell.

I would do the hard way, the higher speed of N2K and the reliance of other nodes as well as the mast head may well cause issues unless you use the right cables. The masthead unit comes with a very long cable and a moulded plug and one field attachable plug so that will not impede drawing through. Also re mast head nodes: When I did my advanced level 0400 NMEA certification course we discussed this because of allowable drop cable length as many are over the stipulated maximum by the time you reach the masthead.That can be overcome this way. Make the masthead unit one end of the backbone and insert an inline terminator instead of the normal one between the masthead unit and the cable.

 

[Norman_E]

Thank you for that. My fear is that however I attach the new cable to the old one to pull it through the joint may break somewhere inside the mast as it seems to follow a convoluted route inside the mast via a conduit at the front to somewhere close to the top, then passing towards the back of the mast to emerge from a grommet fitted hole in the top of the mast crane .

The Garmin MHU instructions online show that the mast cable forms part of the backbone with an inline terminator fitted at the masthead and an inline lightning suppressor at the bottom. B&G don't appear to have put their manual for the MHU online.

Edit: When I have bought all the kit I am going to connect it all together at home and power it from a 12 volt battery in a car jump starter to test everything before I take it all out to Turkey.

 

[David2452]

Difficult but worth the effort Norman, in cases like this I try to minimise parting of the cables risk by carefully removing the inner conductors and inserting the new cable into the outer sheath, then apply a decent length of adhesive lined heat shrink over the joint. Copious amounts of WD or silicone spray on the new cable helps quite a bit. Its not easy but stuff often is not easy to do right. Its really a two bod job, one to feed/push and the other to pull, if the cables become taut from just pulling it increases parting risk of parting and binding. I certainly commend the decision to test the kit before installing as I have had "out of the box" failures, only a couple but sods law dictates that it will be the most difficult to replace part.

 

[Norman_E]

Thank you for that tip about joining the cables, though I may not be able to use it. At the masthead there is only about 3 inches of the old cable plus a big plug, and not much to spare at the mast foot where the cable comes out of the mast, passes through a cable gland and is connected via a chocolate block immediately underneath, so there is hardly any spare length.

I think I might have to attach something like a coil of telephone or alarm system cable at the mast foot, and haul it though the mast from the top then use it to pull the NMEA cable downwards. I think I could join a telephone cable to the old cable by soldering all the cores and then binding with tape. One advantage would be that I have a coil of cable long enough to go right up the mast and back down to deck level, allowing me to solder the NMEA cable to it.

 

[JSYmartini]

There are some good deals to be had on the GMI bundle (display, MHU, depth transducer at the moment.

The great thing is that both the MHU & 'ducer both output N2K, ie no analogue signals into a black box etc. Also they both get power from the N2K network so there's no other wiring, all 3 units simply plug into the network and off you go.

I recently bought the set, didn't realise at first how much info you get:

Speed
Depth
Sea temp
Wind speed
Wind direction
Barometric pressure

Another great feature is the unit logs data so you can look back over a user set period of time and view trends with graphs Etc, particularly good for air pressure.

The only minor disappointment and maybe it was too much to hope for, with the display connected to a garmin plotter via N2K I thought maybe the backlight/contrast display setting might sync themselves but no. Maybe possible via a software upgrade in the future though.

 

[matelot]

. Make the masthead unit one end of the backbone and insert an inline terminator instead of the normal one between the masthead unit and the cable.

More details please. What is an "in line terminator" and what is a normal terminator - outside the cinema that is.

 

[knuterikt]

More details please. What is an "in line terminator" and what is a normal terminator - outside the cinema that is.

The inline is a special kind of connector with a drop cable connection and a built in terminator.
The normal is a terminator to put on the end of a backbone (or on one of the backbone sides of a T connection for drop cable.

Inline terminator

Normal terminator

T-connector

 

[David2452]

Its a terminating resistor at each end of an N2K backbone usually on a Tee with the other two branches connected to the node or drop cable and backbone cable respectively, an inline terminator simply fits between the cable and a node at the end of the backbone eliminating the need for a Tee and drop cable.

 

[David2452]

The inline is a special kind of connector with a drop cable connection and a built in terminator.

No, never used with a drop cable, only at the end of a backbone between the node and backbone cable.

 

[Norman_E]

There are some good deals to be had on the GMI bundle (display, MHU, depth transducer at the moment.

The great thing is that both the MHU & 'ducer both output N2K, ie no analogue signals into a black box etc. Also they both get power from the N2K network so there's no other wiring, all 3 units simply plug into the network and off you go.

I recently bought the set, didn't realise at first how much info you get:

Speed
Depth
Sea temp
Wind speed
Wind direction
Barometric pressure

Another great feature is the unit logs data so you can look back over a user set period of time and view trends with graphs Etc, particularly good for air pressure.

The only minor disappointment and maybe it was too much to hope for, with the display connected to a garmin plotter via N2K I thought maybe the backlight/contrast display setting might sync themselves but no. Maybe possible via a software upgrade in the future though.

I am not completely sure whether to buy the Garmin starter set as you describe or the B&G Triton set. I already have a Garmin GMI 10 instrument, snapped up new for £180 off e-bay and have just won a new Garmin 10metre backbone cable and NMEA 2000 GPS antenna for a bargain price. I can get the Garmin set for under £800, or the B&G for £1000 in round figures. As far as I can see the hull transducer is the same Airmar unit in both sets but the MHU is quite different. The B&G one appears to have a separate base so that it can be removed easily for winter storage, just like my VDO ones. How about the Garmin one? Does your Garmin MHU appear to have good ball bearings on both direction and speed units? I will need more than two displays, so I could perhaps buy the Garmin set and add a B&G Triton display.

Final question, In wind mode does the Garmin unit show True and apparent wind speed and direction simultaneously, like the B&G Triton, which shows both directions on the same screen?

 

[knuterikt]

No, never used with a drop cable, only at the end of a backbone between the node and backbone cable.

It's a small cable (built in drop cable) connecting the GWS10 to the in line terminator

 

[David2452]

That is not a drop cable, its simply a connection and is a part of the node, in the diagram its not described as such and should never be. A drop cable is a cable Teed off the backbone leading to a node, either thick or thin N2K cable not exceeding 6m (the reason for having masthead devices and often rudder transducers at the end of the backbone). Also, forgot to mention, for the OP, try to get the power insertion Tee as close to the masthead end of the backbone as possible to avoid voltage drop, you can plan and verify this with the N2K design software which is free on the Maretron site and saves a lot of time, also you can print a schematic for the network from it to keep aboard.

 

[Norman_E]

One thing I don't understand about the Garmin GWS 10 masthead unit is why they did not build in the terminator so that only a single joint was needed at the masthead.

 

[David2452]

One thing I don't understand about the Garmin GWS 10 masthead unit is why they did not build in the terminator so that only a single joint was needed at the masthead.

Would have made sense only for yachts Norman, I have fitted one to the coachroof of a large sedan cruiser and a built in resistor would have made things very awkward as the backbone on that ran from the rudder to within 8 feet of the bow so a drop cable was more appropriate at about 4.5m from memory, I recall I had to put two power insertion points in the backbone with a power break Tee as the LEN was too high otherwise due to the high number of nodes.

 

[Norman_E]

David, from your experience can you answer my questions above about the Garmin mast head unit? If it does not have a quick detachable fitting I can make a base to fit the VDO fitting at my masthead to enable me to take it down each winter, but I am concerned to know if it has good well protected ball race mechanisms. In Turkey any rain brings down fine abrasive grit which is deadly to unshielded mechanisms, and any plain bearings.

As an aside I really hate having to lose my VDO system because its LCD screens are getting old and failing, as I have two masthead units and both the anemometer and the wind vane run on paired stainless ball races which are easily replaced standard items. If I could work out how to get their output turned into NMEA sentences I would keep them.

 

[David2452]

From memory Norman, if that is a major factor in your decision I would lean to B & G, (the beauty of N2K, it all works regardeless of manufacturer) the Garmin head unit is good quality and the bearings are protected but it is not QD.

 

[knuterikt]

From memory Norman, if that is a major factor in your decision I would lean to B & G, (the beauty of N2K, it all works regardeless of manufacturer) the Garmin head unit is good quality and the bearings are protected but it is not QD.

How do you calibrate the B&G sensor if the rest of the stuff is another brand?

 

[knuterikt]

One thing I don't understand about the Garmin GWS 10 masthead unit is why they did not build in the terminator so that only a single joint was needed at the masthead.

It is not allowed in the NMEA 2000 standard.

 

[David2452]

How do you calibrate the B&G sensor if the rest of the stuff is another brand?

The PGNs in N2K should mean the end of all that nonsense.