NMEA 2000, two pieces of equipment off one drop link?

Ceirwan

Ceirwan

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I'm upgrading my old NASA Marine instruments to a fully integrated NMEA 2000 B&G system.

The backbone is going to run from the Vulcan 7 in the cockpit, to where it terminates at the masthead wind transducer.

At the chart table I have a 4 way splitter and a drop link will go off this into the forecabin area to plug into the Speed / Depth Transducer.
My plan is to install the Rate Compass under the bunk in the same area as its the best location I can find for it.

Is it possible for me to fit a T-Piece in the bunk area and to connect both the transducer and compass to the same drop link off the backbone? Or do I have to run a separate wire from the backbone to the compass as well?
 
I suppose to be NMEA 2000 compliant they should have separate drop cables to the backbone. But I'm sure two instruments on one cable would work. Until recently Raymarine advocated up to three instruments daisy chained off a single drop cable. I guess they've had their knuckles rapped and they don't allow that any more with their latest products.
 
Short answer, no.

At one end of the "backbone" (this can be several cables joined together) you will have a T piece, the end of the T piece will have a terminator fitted to it and the branch will have a drop cable going to the plotter. The other end of this cable can go to anywhere you want, a single T or a string of Ts connected together. So, it can go to the 4 way, you then connect whatever you like to the 4 way with drop cables. From the other end of the 4 way you can run a cable under the bunk and connect it to a couple of Ts for the depth and compass. From the two Ts another cable goes to a final T (with built in terminator) and your mast head wind device connects to this T.
 
PaulRainbow said:
Short answer, no.

At one end of the "backbone" (this can be several cables joined together) you will have a T piece, the end of the T piece will have a terminator fitted to it and the branch will have a drop cable going to the plotter. The other end of this cable can go to anywhere you want, a single T or a string of Ts connected together. So, it can go to the 4 way, you then connect whatever you like to the 4 way with drop cables. From the other end of the 4 way you can run a cable under the bunk and connect it to a couple of Ts for the depth and compass. From the two Ts another cable goes to a final T (with built in terminator) and your mast head wind device connects to this T.
Click to expand...

Except the fact that the B&G MHU (wind) will have a built in terminator and therefore should be one end of the backbone.

My answer to the OP would be.... For NMEA compliance, officially, no.

But for such a short network it would work. Simnet and SeatalkNG are both the same electrically and they allow daisy chaining away from the backbone.
 
Hmm, two different opinions.

I guess the best thing to do would be to try it 'on the bench' as it were.

Unfortunately Paul there is no route for the wiring from the forepeak to the mast, without the wires hanging down outside the internal liner, I have a route from my chart table underneath the bunks to the forepeak, and another route from the chart table, into the overhead panelling and onto the mast.

Edit: It seems that it would work, but won't comply with the standard. Which I'm not fussed about as long as it works.
 
Martin_J said:
Except the fact that the B&G MHU (wind) will have a built in terminator and therefore should be one end of the backbone.

My answer to the OP would be.... For NMEA compliance, officially, no.

But for such a short network it would work. Simnet and SeatalkNG are both the same electrically and they allow daisy chaining away from the backbone.
Click to expand...

Where, from my description, do you think i suggested the wind sensor should be located then ?

If it has a built in terminator he can skip the final T i described and connect straight to the pair of Ts under the bunk. This arrangement is fully N2K compliant and future proof.
 
Ceirwan said:
Hmm, two different opinions.

I guess the best thing to do would be to try it 'on the bench' as it were.

Unfortunately Paul there is no route for the wiring from the forepeak to the mast, without the wires hanging down outside the internal liner, I have a route from my chart table underneath the bunks to the forepeak, and another route from the chart table, into the overhead panelling and onto the mast.

Edit: It seems that it would work, but won't comply with the standard. Which I'm not fussed about as long as it works.
Click to expand...


Just run two wires to the forepeak and it'll be compliant and guaranteed to work.
 
Although if running two wires as individual spurs then they could each need to be <6m to be compliant.... This is the reason you cannot put a T at the mast base and spur the Wind MHU from it...

If it's longer then a 6m run from the chart table then next option up might be a couple of ten metre backbone cables to the forepeak with devices spurred off within the forepeak.

Not sure on the Vulcan but other B&G chart plotters are able to display NMEA2000 bus statistics so you can see if there are any errors etc... So at least you have a way to check bus performance and can keep an eye on utilisation.
 
No, the boats only 8.4m long so I don't really have to worry about Spur length.

Just trying to save buying another 5m cable (and having to run it) if its not strictly necessary.

I've got all the bits at home, so I'll just hook it up to my 12v power supply and see what happens.
 
PS. Remember the fuse in the power supply... If you've got the B&G NMEA 2000 kit it's included in the wire but some kits don't have a fused power connector.



Buy a spare fuse or two if needed.
 
Martin_J said:
Although if running two wires as individual spurs then they could each need to be <6m to be compliant.... This is the reason you cannot put a T at the mast base and spur the Wind MHU from it...
Click to expand...

I didn't say spur from a T. I said continue the backbone from the 2 ts under the bunk, to a connector with a built in terminator (inline) at the mast head. This is N2K compliant. If the B&G unit has this built in, just continue the backbone from the 2 Ts and connect straight to the unit, as i said before.
 
Ceirwan said:
No, the boats only 8.4m long so I don't really have to worry about Spur length.

Just trying to save buying another 5m cable (and having to run it) if its not strictly necessary.

I've got all the bits at home, so I'll just hook it up to my 12v power supply and see what happens.
Click to expand...

You can run two spurs to the forepeak, or you can run the backbone to the forepeak, to two ts, then back again.
 
Martin_J said:
Except the fact that the B&G MHU (wind) will have a built in terminator and therefore should be one end of the backbone.

My answer to the OP would be.... For NMEA compliance, officially, no.

But for such a short network it would work. Simnet and SeatalkNG are both the same electrically and they allow daisy chaining away from the backbone.
Click to expand...

Can you post a link to a diagram where more than one sensor is connected to a single drop cable please.
 
Martin_J said:
Although if running two wires as individual spurs then they could each need to be <6m to be compliant.... This is the reason you cannot put a T at the mast base and spur the Wind MHU from it...

If it's longer then a 6m run from the chart table then next option up might be a couple of ten metre backbone cables to the forepeak with devices spurred off within the forepeak.

Not sure on the Vulcan but other B&G chart plotters are able to display NMEA2000 bus statistics so you can see if there are any errors etc... So at least you have a way to check bus performance and can keep an eye on utilisation.
Click to expand...

Vulcans can display NMEA2K bus statistics if asked nicely :p
 
PaulRainbow said:
Can you post a link to a diagram where more than one sensor is connected to a single drop cable please.
Click to expand...

The IS40 B&G screens can be daisy chained off a spur, and actually have two Micro C connections to allow this. Although its not inline with the standard.
I think the newer Triton 2 displays have removed this feature.
 
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