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  #1  
Old 12-20-2012
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Installing Maretron wind instrument at the stern

I wanted to run this idea by you guys. My wind instrument is well and truly dead, but to replace the masthead one, and run wires down the mast, will probably require removal of the mast - which I'm not prepared to do right now.

However, the Maretron solid-state instrument, WSO-100, opens up the possibility of stern mount. I am thinking of putting it on top of a 6ft pole at the stern, so it will be approx. 9 ft off the water.

According to the Wikipedia entry on wind gradient,


once you get 2 meters off the water, the further vertical gradient is very slight - so the difference between the reading I get and the wind speed at the top of the sail will also be small.

The only other drawback I can think of is that when very close hauled the instrument might be in turbulent air off the main sail - but I'm not sure this is likely. There will be a considerable gap still, between the instrument and the mainsail's leech. How far does the boundary layer extend from the inside edge of the sail?

Also when steaming straight up wind there might be an error.

But to put this into perspective, my neighbour relies on a hand-held wind meter. I was using a 30-yr old IMI meter with broken direction indicator. Surely the stern mounting will still work well enough to be useful? Note that the Maretron has no error up to 30% tilt, unlike a mechanical gauge.
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Old 12-20-2012
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Re: Installing Maretron wind instrument at the stern

Although wind speed is measured 10 meters above sea level, there will not be too much difference. The effect of sails on direction will be much pronounced. The only placeforproper wind direction measurement is unfortunaltely the top of the mast. The sails will change the direction of the wind in any direction of your sailing.

Do not stern mount. It is generally more easier and cheaper to climb the mast for such changes.
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Old 12-20-2012
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Re: Installing Maretron wind instrument at the stern

Mark:

Will you be using the sensor to drive an AP? Masthead is ideal IMHO. But in the interim, your idea is OK, depending upon how much trouble it would be to setup your stern mount. If it involves penetrating the deck, I'd stick w/option A, bite the bullet and put it on the masthead.

Now as far as running N2K backbone cable up your mast, I suggest you make sure the terminating resistance is correct. We had to redo ours due to some unpublished engineering changes w/our Airmar unit and cabling.
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Re: Installing Maretron wind instrument at the stern

First of all, I would disagree with the interpretation that Wikipedia's says that wind gradients only extend 2 meters. As any mainsail trimmer worth his salt can tell you, in light to moderate breezes and in thermal stratification conditions, the impact of wind gradient can extend well above the masthead. Even the article on Wikipedia aludes to this in their discussion of 'twist'.

But in my mind, the impact of wind gradient would not be the reason not to mount wind instruments down near deck level. The air flow around a boat is warped by the shape of the hull, house, rigging and etc. on all points of sail, not just upwind. Within that distortion are significant velocity (i.e speed and direction) changes that would alter the accuracy of the data obtained by the sensor to the point of making it meaningless at times, and if data can't be trusted, it is argueably not useful at any time.

Even masthead instruments are in part impacted by updraft off the sails, and by the air flow shifts around solid objects around the masthead. But this location experiences the least amount of induced flow changes which is why it is the typically selected location to mount wind sensors.

In terms of mounting new equipment, there are several options which may not require new wiring. Most wind instruments use four wires harnesses, and so you may be able to use your existing wiring harness but splice on new connectors for the updated equipment. (That is what I did.) You can also buy wireless wind instruments and from what I gather, these have a had good track record.

Jeff
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Last edited by Jeff_H; 12-20-2012 at 08:47 AM.
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Re: Installing Maretron wind instrument at the stern

As someone has already mentioned the old cabling is probably fine so no need to lower the mast or go wireless and use TickTack which is now part of Ray Marine. Believe most of the last charter companies have gone this way for low maintenance.
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Re: Installing Maretron wind instrument at the stern

Hey,

I would use the stern mount for now and then move it to the masthead when it's more convenient. It won't be perfect on the stern but it will be better than nothing.

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Re: Installing Maretron wind instrument at the stern

Quote:
Originally Posted by arisatx View Post
Mark:

Will you be using the sensor to drive an AP? Masthead is ideal IMHO. But in the interim, your idea is OK, depending upon how much trouble it would be to setup your stern mount. If it involves penetrating the deck, I'd stick w/option A, bite the bullet and put it on the masthead.

Now as far as running N2K backbone cable up your mast, I suggest you make sure the terminating resistance is correct. We had to redo ours due to some unpublished engineering changes w/our Airmar unit and cabling.
Thanks for the replies everyone!

Yes I heard that the Airmar units had a terminating resistor installed internally for a while, which is not compliant with the NMEA 2000 standard, so they took it out. Could be confusing.

To the poster that suggested using the existing wiring, I see that NMEA 2000 is 4 wires plus shield. If I have decent looking 4 wire shielded cable (which I do), is this likely to work for NMEA 2000 with the correct terminations, or is there something special about the bandwidth?

I have gone off the stern mount idea after finding some diagrams of air flow around sails, and seeing that there will be a very significant direction error when close hauled (we're talking 20 to 30 degrees)
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