NMEA 2K branch lengths?

9D280 · 13 January 2012, 12:10

Is there a maximum length of "branch" on an NMEA 2K network?

I will soon be wiring the plotter, and for simplicity and keeping as many of the connections undercover as possible, I am thinking of putting a single "T" near the head, and running a single branch to the A- frame for the GPS pod and eventually continue the backbone to the engine (part of a long term plan to instrument the engine).

Net result of this is going to be the best part of a 5m "branch" to the GPS pod. is that too long, or is the branch length inconsequential?

BruceB · 13 January 2012, 15:55

5m is nothing. NMEA network limits don't even come close to what you would have no matter how you wired a RIB network

Ian M · 13 January 2012, 16:17

Lowrance quote a NMEA 2000 network backbone maximum length of 100 metres, but also state that any device should not be more than approximately 6 metres from its 'T' connector.
Set up info here http://www.lowrance.com/upload/Lowra...173_112006.pdf

martini · 13 January 2012, 17:50

Maretron say that the sum total length of all drop lines should not exceed 256 feet so you should be ok

BruceB · 13 January 2012, 19:02

Would it not be neater to go to the outboard first and then up to the aerial, putting the terminator on T piece inside the cowling?
This is how I have done mine and at least the last connection is under cover out of the elements.

Poly · 14 January 2012, 12:10

NMEA2000 on that engine.

Its funny enough having it on the boat

Daniel · 14 January 2012, 12:38

I always thought it was 6m in any one drop. I install a fair new systems, and thats the rule I follow.

BruceB · 14 January 2012, 17:46

Quote:

Originally Posted by Polwart

NMEA2000 on that engine.

Its funny enough having it on the boat

Actually I only just noticed this, you don't get an interface for an engine that old anyway. The best you could get was the fuel flow sensor which could be mounted at the fuel tank. Assuming this is under the seat then the branch doesn't need to go to the rear.

Poly · 14 January 2012, 18:16

Bruce, I may have dreamt this but I think you can get a box which will let you wire any sensor or alarm in and it will broadcast it onto your network, if you set it up right. Bet it is not cheap though.

Erin · 14 January 2012, 18:26

Quote:

Originally Posted by Polwart

Bruce, I may have dreamt this but I think you can get a box which will let you wire any sensor or alarm in and it will broadcast it onto your network, if you set it up right. Bet it is not cheap though.

Actisense are leaders in this field. I think you will find that most of the guidance on drop lengths and backbone lenghts are all realted to obtaining and complying with nmea certification. Out in the field you'll be suprised at how far you can push those supposed boundaries and still have a fully working system. An old article on Panbo.com illustrated this neatly.

Chris · 14 January 2012, 18:36

Dont forget there is no need to mount the GPS aerial on the Aframe in the first place. Most of the modern GPS aerials will work even if they are inside the console.

If you do decide to go down this route I may have a spare 25ft NMEA cable available for a good price.

Pikey Dave · 14 January 2012, 22:52

[QUOTE=Chris;439063]Dont forget there is no need to mount the GPS aerial on the Aframe in the first place. Most of the modern GPS aerials will work even if they are inside the console.
QUOTE]

I'm in the process of fitting AIS, the recommendation is to mount the GPS antenna as low down as possible to reduce fluctuations due to rolling. It's going inside the console.

Pikey Dave · 14 January 2012, 22:54

Quote:

Originally Posted by Chris

Dont forget there is no need to mount the GPS aerial on the Aframe in the first place. Most of the modern GPS aerials will work even if they are inside the console

I'm in the process of fitting AIS. The recommendation is to mount the GPS puck as low as possible to reduce fluctuations due to rolling. It's going in the console, out of the way.

9D280 · 16 January 2012, 10:27

Quote:

Originally Posted by Ian M

Lowrance quote a NMEA 2000 network backbone maximum length of 100 metres, but also state that any device should not be more than approximately 6 metres from its 'T' connector.
Set up info here http://www.lowrance.com/upload/Lowra...173_112006.pdf

Ian, cheers, that's the sort of info I was after. As many have said, not a problem on my boat!

Quote:

Originally Posted by Polwart

Bruce, I may have dreamt this but I think you can get a box which will let you wire any sensor or alarm in and it will broadcast it onto your network, if you set it up right. Bet it is not cheap though.

Or just buy "plug in" themal & pressure sensors from Lowrance or the other crowd that does them at around £70 each. Current plan is a pressure sensor hanging off the cooling system and a thermal strapped to the head. May also add a fuel flow, but right now the aim of the game is to warn me it's about to go bang seeing as it has absolutely nothing in the way of warnings other than noticing the telltale has stopped.

And before you all ask why use NMEA - the cost of the sensor is in the ballpark of what I would pay to get a separate analogue gauge & sensor, so why drill more holes in my console for gauges that there is no space to fit anyway when I can set a couple of alarms on the plotter.

Quote:

Originally Posted by Pikey Dave

I'm in the process of fitting AIS. The recommendation is to mount the GPS puck as low as possible to reduce fluctuations due to rolling. It's going in the console, out of the way.

I can maybe see that on a yacht, or the bridge of a cruiser, but surely a clear view of the sky is going to reduce error a lot more than the movement due to roll of a Rib A- frame? With lots of good satellite signals & WAAS engaged you are looking at a guestimated metre or so accuracy. It's not like you need milimeter level accuracy for something that will put you a metre to the left if you rolled 90 degrees while you are horsing along at 20 plus knots.

Can't argue with the tidy comment tho!