Masthead wind instruments NMEA 2000 or 0183?

[ronstory]

All--

First post. but i'm not shy.

We purchased a C&C 35 MarkII (1974) and the good/bad news the electronics is an analog knotsmeter and separate depth plus a bones-simple VHF radio. So I have a wide open canvas as to paint.

I want to have masthead wind instruments but I'm trying to understand what to buy. Background, I have purchased a Raymaring EV-100 wheel pilot and a C97 MFD and replaces analog knotsmeter tranducer with a DST800 tri-ducer that his NMEA2K complaint.

So I'm now trying of figure out what to put at the top of the masthead for wind instruments. Looking at the NMEA2K spec, it states the the maximum drop length for NMEA2K devices is 6 meters. With the mast being 45 foot tall, I'm trying to figure out if I need to:

1. Run the backbone up the mast and then link the masthead instrument via NMEA2k.
2. Maretron and Airmar seem to have drop NMEA2K cables that are longer than 6 meters, so i'm trying if figure out the rules with length and termination.
3. Go with old school NMEA 0183 wind instrument (rs232/442) and use a bridge to map them to the NMEA2K network.

I like the idea of the Maretron and Airmar ultrasonic wind instruments since they have no moving parts... but I'm wondering if they will work with the Raymarine instruments on the network.

All feedback in appreciated. ;^)

Thanks, Ron
Portland, OR

[CaptWil]

Welcome Ronstory

Well I have done exactly what you are looking at doing. Airmar Ultrasonic weather station to a B&G Triton 31, NMEA 2000 backbone, and a Shipmodul Multiplexor 3 Wi that will allow conversation 0183, 2000, Seatalk vice versa

ShipModul Marine Electronics

Cheers
Will

[ronstory]

Will--

Thank-you for the pointer! Also, did you run the N2K backbone up the mast or are you using the 0183 interface from the Airmar to the network?

Thanks,
Ron

[CaptWil]

Hi Ron

Running the cable as much better to have as N2K; also I have to renew all my electrical wiring up the mast so it made sense for my case anyway

Cheers
Will

[Pyxis156]

Ron,

You need to run the backbone up the mast. Many if not most N2K masthead wind instruments have a terminating resistor built in to deal with this. If you can get the cable up the mast, it is pretty painless hooking up the actual instrument.

However, in the case of the Maretron and Airmar ultrasonic instruments, I believe you will have to add a terminating resistor. At the end of the cable install a tee connector and put the terminating resistor on the end and plug the wind instrument into the tee with a short pigtail N2K cable. If you have access, to protect things you can keep the tee and resistor in the mast and just run the pigtail out to the wind instrument.

Hope this helps...

[ronstory]

Ok, I think I got it. Run the N2K backbone up the mast, protect and seal all the needed connections and termination in the mast where possible and just run the drop cable to the instrument.

Thanks,
Ron

[george123]

You can add an in line terminator to the cable that you run up the masr. No need for a T or drop cable. The side of the inline terminator that is open you just screw that into the Maretron or airmar. I have done this on a 43 HR sailboat. If you use Mareton cables an T they are water tight.

[ronstory]

Hmm... Interesting. So if I use the inline termination with the Airmar or Maretron, is the wire up the mast a backbone or a long drop cable at the end of the backbone so the termination works?

Thanks,
Ron

[george123]

The inline terminator is designed so that you can connect a device at the end of the backbone. You can look at it as a T, drop cable, and resistor all in one. I have attached a drawing that shows what my installation looks like.

[Dockhead]

As others have advised you already, the standard way to do this is run the backbone up the mast and terminate it there with a termination resistor.

You buy bulk cable in the length needed and attach a field-connectable terminal to it. Pay attention to good weatherproofing of the terminal -- I used shrink tube and rescue tape.

As for the instrument itself, one to consider is the ultrasonic Maretron WSO-100, which has no moving parts. Has no vane to bounce around in a seaway, which is a big plus. There will be no issue with displaying the data on any N2K display. One of the several great advantages of N2K is far greater compatibility. My personal favorite wind display is the B&G Triton, which shows apparent and true in analogue and digital form on one screen.

One issue with the WSO100 and other ultrasonic wind instruments is getting the instrument into clean air. It comes with a standard antenna pole mount socket, and it won't work if it is right on top of the masthead truck. I used an antenna pole base and had 1 meter alu pole made. The ready made poles are stainless and I felt they were too heavy -- would tend to work loose. You might consider a cranked pole that would get the instrument forward as well as up -- that will help get into cleaner air.


Maretron have a handy, free design program to help you design your N2K network. If you can eliminate all NMEA0183, you will be happy, but if you do end up with some item of 0183 gear, most plotters can deal with one 0183 talker, and bridge the data to the N2K network. If you have more, then you will need a multiplexer, which the complexity of the network starts to snowball, which is obviously undesirable.

Feeding radios with 0183 position data, however, is no problem, as the single 0183 output from a plotter can drive several 0183 listeners. It's also pretty simple to set them up with a freestanding GPS, something some of the experts here advocate for safety reasons.

For GPS, look at the Simrad GS25. This is a category-killer -- for only $200, it receives both GPS and GLONASS, and does DGPS (WAAS and EGNOS) both in the U.S. and Europe. I get sub-2 meter accuracy with mine. Maybe other makers are now offering something similar. Don't be tempted to use the built-in heading sensor to drive your pilot, though.

[Mycroft]

I went with the Airmar WS-200WX. It was twice the cost of the Maretron unit, but from my research, it appeared to be more reliable, and at the top of the mast, I want reliable. Plus it provides a good bit more information.

The Airmar connector cable for it (WS2-C30) has the terminating resister built into the cable. You can risk trying to feed the N2K connector down through the mast or cut it off and connect a field terminator, which is what I did. Field terminators are a real PITA. I had hired a rigger to run my mast cables and bowed to his recommendation to snip the end off. If I were doing it myself and that was the only cable I was feeding through, then I'd probably try keeping the connector on with the first attempt.

The riggers got the LMR-400 cable pulled through slicker than spit. But ironically, the slim N2K cable really gave them fits. Possibly because the old cable being used as a pull-string had gotten newer cable runs twisted around it at some point. So at their hourly rate, snipping the terminator off was the right call. Leaves a nice uncut waterproof connection at the mast top.

[Dockhead]

Originally Posted by Mycroft

I went with the Airmar WS-200WX. It was twice the cost of the Maretron unit, but from my research, it appeared to be more reliable, and at the top of the mast, I want reliable. Plus it provides a good bit more information.
. . .

The Airmar 200 has a compass and GPS built in, which are useful on a powerboat where the unit is mounted closer to the roll and pitch centers of the boat, but the masthead of a sailboat is a terrible place for these sensors.

If you want to go with Airmar, better the 100 model which doesn't have those sensors. Definitely put the GPS and compass in places don't swing around. For the compass, this is particularly important. I use the Airmar H2183 compass.

As to Maretron vs Airmar for the wind instrument, I don't have any information. It used to be that the performance was about the same. But I heard somewhere that Airmar have made some breakthroughs in the software used to produce wind angle from the ultrasonic data, so maybe these are now performing better.


There is some confusion about what sensor inputs are used to produce what data on these units. Much of this confusion results from the use of the term "true wind" in Airmar's literature. Note that these units are primarily designed for weather stations, and so they are using "true wind" in the land sense of wind in relation to North, what we call "ground wind". The Airmar 200 will calculate ground wind using the compass data, but this is useless on a boat because our systems calculate their own ground wind using the boat's primary heading sensor, and will not even recognize the ground wind data put out by the Airmar unless specially programmed to do so.

The compass and GPS in the Airmar 200's are also set up to switch themselves off if they detect heading and position data on the network, so millions of Airmar 200 users are sailing around, without knowing it, with all of the sensors switched off except the wind sensor. They might as well have saved their money and gone with the 100. The accelerometers in the Airmar 200 compass are used solely to correct heading data, and play no role in the AWA or AWS data. There is a lot of confusion about this in the Internet caused by people just believing that the wind data must be corrected, and therefore just making up nonsense, because the wind data from their ultrasonic instruments so vastly much more stable than the wind data from a mechanical wind instrument, but in fact that is the result of the nature of the instrument, not correction by accelerometers.

There are two reasons why the wind data is more stable from an ultrasonic instrument, than from a mechanical one:

First of all, there is no mechanical vane with its own inertia causing complex (and thus hard to correct) distortions to the data;

And, mechanical wind sensors send truly raw data -- reflecting nothing but the position of the vane at any given moment, as no processing of the data is done at the masthead. Ultrasonic sensors send calculated data which has already undergone one level of processing. Because the distortions of the data from an ultrasonic instrument have no component of the inertia of a mechanical sensor, they are easier to correct for motion of the masthead. You don't need accelerometers to make this correction, as you can just average the high and low readings over the roll and heave periods which are easily calculated. The data from a mechanical sensor is far more complex, because the vane overshoots due to inertia, and will overshoot non-symmetrically, because of gravity effects on a heel.


For ultrasonic wind sensors superior to either Maretron or Airmar, have a look at LJ Capteurs transducers. Unlike either Maretron or Airmar, these are specifically designed for sailing. They are lighter and smaller, and have a totally superior mounting system using an angled carbon rod. I did not go with these in my own installation because they were (at that time) hard to obtain, and because they do not speak N2K natively, making for a complex installation. But still worth a look for the other advantages, and there is apparently an N2K (Canbus) version now.

And -- for anyone intimidated by pulling cables, LJ Capteurs makes a wireless, solar powered unit. This could be installed without pulling the mast down -- looks terrific. However, it only sends data every 15 minutes at night.

[ronstory]

Sorry for the slow response, work interfered with life again. ;^)

I saw the LCJ Capteurs mentioned on a couple of website, but could not seem to find any real reviews. I now see the Fugawi in Canada is selling them and while I don't like running a long run of 0183 line from masthead to the MFD mounted on the binnacle, it may just work with the Raymarine C97 0183 interface. If not, I could do their 'new' Windyplug

WINDYPLUG - LCJ Capteurs

which seems to replace the older larger box that is Fugawi still advertises.

Has anyone actually used the LCJ Capteurs on a sailboat? I would love to know if it just worked with Raymarine stuff.

Thanks,
Ron