NMEA Cable

[Houleaux]

I recently fitted a Standard Horizon radio with AIS to my boat. I wanted to interface this with my CP180 chart plotter but unfortunately the cable supplied was far too short.

Having tried unsuccessfully to buy a length of NMEA cable and not wanting to put the boat back together without finishing the job, I hunted around for something that might be suitable. I found what I think was telephone cable (4 very light wires in a 'flattened' - as opposed to round - white insulation) and used that to extend the NMEA cable by the required 2 metres - soldering all the joints to ensure a good connection.

All appears to be working fine. The position information is displayed on the radio and the AIS information on the chart plotter.

So is telephone cable a cheap and reliable substitute for NMEA cabling, or is there a downside to its use that I haven't (yet?) identified?

I should perhaps make it clear that this cable is only used for data and not for power.

 

[ianj99]

I recently fitted a Standard Horizon radio with AIS to my boat. I wanted to interface this with my CP180 chart plotter but unfortunately the cable supplied was far too short.

Having tried unsuccessfully to buy a length of NMEA cable and not wanting to put the boat back together without finishing the job, I hunted around for something that might be suitable. I found what I think was telephone cable (4 very light wires in a 'flattened' - as opposed to round - white insulation) and used that to extend the NMEA cable by the required 2 metres - soldering all the joints to ensure a good connection.

All appears to be working fine. The position information is displayed on the radio and the AIS information on the chart plotter.

So is telephone cable a cheap and reliable substitute for NMEA cabling, or is there a downside to its use that I haven't (yet?) identified?

I should perhaps make it clear that this cable is only used for data and not for power.

For a 2metre run, the phone cable is perfectly adequate.
I've used 8core alarm cable of a similar length handling nmea, seatalk and power with no problems.

 

[prv]

I don't think there's any such thing as special "NMEA cable".

The signalling protocol employed is (by modern standards) slow and clunky; this has the benefit of working through all sorts of marginal connections. I've been on boats using everything from mains flex to bell-wire to individual strands, connected by soldering through choc-blocks to twist-and-tape, and it's all worked adequately.

Not that I'm recommending others follow those examples, of course.

Pete

 

[yachtorion]

Trailer cable.

I've had surprising success with mixed power and NMEA data running over 7 core trailer cable over a few meters. It's cheap and readily available

 

[lustyd]

I think the baud rate was chosen to ensure connectivity in any circumstances. After all, NMEA was put together long after 4800 would have been considered current or up to date. As Pete says, you could probably use jelly babies and get a decent connection with modern electronics.

 

[David2452]

I assume we are talking about 0183, in which case though there is no such thing as NMEA0183 cable, there is a specification for it and a specification as to how it should be connected, The correct cable is a multi strand tinned single twisted pair shielded and around 24AWG, grounded via the shield at the talker end. Of course almost anything will work but to give it the best chance of working at its best and continuing to do so and as I pay under £2 a metre for the correct spec I see no reason not to do it using the right stuff. That and the fact I can’t sign the job off as compliant unless I do. A lot of telephone cable is single conductor and in my view single conductor cable of any sort has no place on a boat.

 

[prv]

A lot of telephone cable is single conductor and in my view single conductor cable of any sort has no place on a boat.

Agree - but the OP talked about "flat cable", which is usually found in trailing extension leads rather than cable intended for installation, and therefore is multi-strand rather than solid.

Certainly didn't mean to suggest that just because it can work along a couple of strands of barbed wire, a professional shouldn't do a professional job with the proper materials.

Pete

 

[lustyd]

I assume we are talking about 0183, in which case though there is no such thing as NMEA0183 cable, there is a specification for it and a specification as to how it should be connected, The correct cable is a multi strand tinned single twisted pair shielded and around 24AWG, grounded via the shield at the talker end. Of course almost anything will work but to give it the best chance of working at its best and continuing to do so and as I pay under £2 a metre for the correct spec I see no reason not to do it using the right stuff. That and the fact I can’t sign the job off as compliant unless I do. A lot of telephone cable is single conductor and in my view single conductor cable of any sort has no place on a boat.

Thanks I honestly didn't know there was a standard for the cable. In that case I'll eat the jelly babies

 

[Bloater]

It may work quite well with a piece of wet string and continue to do so, however the answer to your question is primarily the lack of a screen.

The wiring may be susceptible to electrical interference (eg it could stop working one day when perhaps someone operates a microwave nearby), or it could give out interference itself, perhaps disrupting gps reception.

As I said earlier, you might not ever have a problem.

 

[maby]

Thanks I honestly didn't know there was a standard for the cable. In that case I'll eat the jelly babies

There's a standard for almost everything these days! I suppose it's there to protect the manufacturer from claims due to user stupidity...

Actually, the true interface definition for NMEA0183 is RS422, not RS232.

422 is a balanced interface which has a high resistence to interference and can carry data long distances at high speed. Most chartplotters can be switched to RS232 which is necessary to talk to devices like computers. Your CP180 plotter seems to only support RS232 - it needs fewer wires than RS232 which allows the manufacturer to squeeze more functionality onto a standard plug.

 

[Dazzajohm]

Hello...

Just picked up on this thread as I'm looking on how best to extend an NMEA cable from my SH GX2200e to my E7d. I'm probably only going to need an extra half metre for which I'm thinking of using cat6 cable but I'm wondering whether there is an easy way to connect the cables together.

I notice the originator of this post said he soldered all the connections, however I've not soldered since I was at school so a little nervous about doing so and was wondering whether I could use some very small choc blocks on each end?

Has anyone used this method with any success?

Cheers

 

[lpdsn]

Not a great fan of choc blocks. Although if the area is dry it won't be all that bad. I generally use terminal blocks and 4mm ring terminals. NMEA 0183 is not exactly GigaBit.

 

[Poey50]

I spliced in some four strand telephone cable to extend the control panel on my Planar heater. 2 way gell-filled connector crimps seemed to do the job. https://www.amazon.co.uk/Way-Gel-Filled-Connector-Crimps-Packet/dp/B007FGYV3Y

 

[Muddy Boat]

I have just done this job and struggled to find cable of the correct spec to buy that wasn't on 150m rolls!

Eventually I found this at Farnell which was the closest they sold by the metre: Belden 8723 SHLD CABLE, 2 PAIR, 22AWG, GREY.

As you can see this is 22AWG rather than 24, but as the distances were only a few metres I figured it would be fine! It also has 2 pairs which I chose as I will potentially be running different baud rate data into multiplexor. i.e gives a bit of futureproofing.

 

[prv]

As you can see this is 22AWG rather than 24, but as the distances were only a few metres I figured it would be fine!

AWG is a back-arsewards American system - you've actually over-specced rather than under

Pete

 

[Muddy Boat]

AWG is a back-arsewards American system - you've actually over-specced rather than under

Pete

I must say that I was questioning it as I wrote it as I thought something didn't feel right . I have now checked the NMEA specs that I have and they say:

'Interface cables, regardless of length, shall be composed of multi-conductor tinned shielded cable with a minimum 95 percent shielding. A twisted pair employing 22 AWG stranded wire shall be used for the NMEA 0183 data signals. NMEA 0183-HS requires a third conductor, which is used to ensure that the common mode ground potential is the same at all drivers and receivers.'

So, the Belden 8723 cable I used conformed with these specs and not the 24AWG suggested by the earlier poster.

Thanks for pointing this out Pete and hope this helps clarify.

 

[Dazzajohm]

We'll today I managed to use my cat 6 cable and some termination blocks to extend the NMEA cable between the radio and plotter. Worked a treat. Some people had said getting the two units to talk to each other can be fiddly but mine all worked perfectly.

Thanks to everyone for their suggestions.