Wind Sensor on Bimini

[alanfw]

I've been mentally wrangling with the idea of adding a wind sensor (replacing the old one that hasn't worked since I bought the boat). I'm troubled by the difficulty of placing a new one on masthead - the existing one is VDO and it looks like the bracket would make replacing it with another VDO fairly easy. But it seems like VDO is not a good alternative. For this reason I'm considering placing the sensor on the rear of the bimini, aft of the solar panels (see photos). Has anyone tried a similar installation?
My overall intention is to network the wind sensor, GPS, and Simrad TP32 tiller pilot to allow me to sail-to-course or sail-to-wind. It also gives me the advantage of seeing the wind better at night (otherwise, when sailing with manual helm I'm happy with tell-tales, shroud streamers, and windex). I know there will be disturbance when close hauled, shifting the apparent wind but that shouldn't create problems as long as I'm aware and can make allowances accordingly. I also understand it won't be as true that close to the sea surface, but is it bad enough to render the information useless? Is there much difference?

[SailingHarmonie]

As you might imagine, there are a lot of really good reasons that people go to all the trouble to put wind transducers at the top of the mast.

Sails, and other boat parts, dramatically change the direction of the air flow. Minor changes in sail trim will have quite large changes in the direction of the air flow hitting a sensor at deck level. Any calculation of true wind will be so far off as to be worthless. It will also result in apparent wind angle measurements that are highly unstable as the boat heels and changes course.

This would fall into the "not recommended" category. But it is your boat...

[alanfw]

Originally Posted by SailingHarmonie

...
This would fall into the "not recommended" category. But it is your boat...

Obviously "not recommended"! (although many racing dinghies and some racing yachts have indicators/sensors placed other than at masthead)

But when the recommended option is prohibitively difficult/expensive, it would be nice to know HOW MUCH difference would be found by placing the sensor there... And there is always the option of repositioning the sensor when standing rigging is replaced. So I'm asking for the experiences of those who might have tried it.

[CatLove]

Originally Posted by alanfw

I've been mentally wrangling with the idea of adding a wind sensor (replacing the old one that hasn't worked since I bought the boat). I'm troubled by the difficulty of placing a new one on masthead - the existing one is VDO and it looks like the bracket would make replacing it with another VDO fairly easy. But it seems like VDO is not a good alternative. For this reason I'm considering placing the sensor on the rear of the bimini, aft of the solar panels (see photos). Has anyone tried a similar installation?
My overall intention is to network the wind sensor, GPS, and Simrad TP32 tiller pilot to allow me to sail-to-course or sail-to-wind. It also gives me the advantage of seeing the wind better at night (otherwise, when sailing with manual helm I'm happy with tell-tales, shroud streamers, and windex). I know there will be disturbance when close hauled, shifting the apparent wind but that shouldn't create problems as long as I'm aware and can make allowances accordingly. I also understand it won't be as true that close to the sea surface, but is it bad enough to render the information useless? Is there much difference?

Another option, perhaps as bad as on the bimini would be in the front of the bow on a bowsprit:

[Knotical]

One experiment you can do is loose wire the wind sensor where you want it (using zip ties, straps etc.), network it, and go for a sail in moderate to heavy winds - sail manually on different points of sail and note SOG and heading, now switch to AP in wind-vane mode and note those again, there will definitely be a difference, especially upwind, if you can live with that difference you are fine.

I love sailing in wind-vane mode, it is truly a press and forget kind of deal if you are expecting steady winds.

[alanfw]

Originally Posted by Knotical

One experiment you can do is loose wire the wind sensor where you want it (using zip ties, straps etc.), network it, and go for a sail in moderate to heavy winds - sail manually on different points of sail and note SOG and heading, now switch to AP in wind-vane mode and note those again, there will definitely be a difference, especially upwind, if you can live with that difference you are fine.

I love sailing in wind-vane mode, it is truly a press and forget kind of deal if you are expecting steady winds.

That's a nice idea! It will be REALLY easy to temporarily mount on the Bimini and route cables.

[GordMay]

The WMO standard is to measure surface wind speed at a height 10 meters (32.8 feet), and the distance, between the anemometer and any obstruction, is at least ten times the height of the obstruction.
Because of the relatively smooth water surface, and lack of obstructions [except on a boat ], wind speeds do not decrease as much, close to the sea, as they do on land.

In general, the following formula will provide a multiplier, to compensate for lower height anemometer (where H is the height of the anemometer in metres above ground level):
Multiplier = 1/[0.233 + 0.656*log10 (H+4.75)]

eg: at only 2.0m high: multiplier = 1.29
at 3.0m: multiplier = 1.22
at 3.5m: multiplier = 1.20

[alanfw]

In my context, the interest is direction of wind as it's used by the tiller pilot.
Wind speed may be interesting, but in terms of boat management, feel and vision is sufficient.

[cr180]

Go for it. I’m with you, over messing with mast head transducers. Not reliable. Let us know how it works out!

[BobFord]

Interesting thread- in my case the ST60 top of mast ,has corroded plug and really needs a new down cable ( a really costly exercise) Noted above was installation of transducer on bowsprit !! In my case , main wind angle , beam and forward of beam ,is most needed . Hence , distance to receiver is relatively short (15meters ) and a cable free unit will ,apparently , work. Comments appreciated.

[wholybee]

Originally Posted by SailingHarmonie

As you might imagine, there are a lot of really good reasons that people go to all the trouble to put wind transducers at the top of the mast.

Sails, and other boat parts, dramatically change the direction of the air flow. Minor changes in sail trim will have quite large changes in the direction of the air flow hitting a sensor at deck level. Any calculation of true wind will be so far off as to be worthless. It will also result in apparent wind angle measurements that are highly unstable as the boat heels and changes course.

This would fall into the "not recommended" category. But it is your boat...

There are a lot of really good reasons to get it off the masthead as well. The rocking movement of the mast will cause both the apparent windspeed and direction to change, sometimes by huge amounts. Sometimes enough to make any autopilot the relies on them to perform poorly. And sails cause an updraft the causes both windspeed and direction to be incorrect at the masthead as well.

[SailingHarmonie]

Originally Posted by alanfw

Obviously "not recommended"! (although many racing dinghies and some racing yachts have indicators/sensors placed other than at masthead)

But when the recommended option is prohibitively difficult/expensive, it would be nice to know HOW MUCH difference would be found by placing the sensor there... And there is always the option of repositioning the sensor when standing rigging is replaced. So I'm asking for the experiences of those who might have tried it.

Nobody can tell you how much difference you would see. It depends on the environment around the transducer, where it is relative to the sails, other boat parts, how much does your boat heel, what conditions do you sail in, etc, etc.

If you want to do it, just try it. You do not need the internet's approval. See if it works for you. If you are happy with the performance, nobody can tell you it is wrong. Mount it permanently after you find a place where the performance of the AP is satisfactory to YOU. Nobody else matters. I'd suggest trying a place close to the centerline, and as far from sails as possible.

In my case a bow pulpit mounted instrument would be a good second choice--right up until the first ocean wave took it out. But that might not be a concern for you.

If all you want is to hold an apparent wind angle with the AP that is possible. All you have to do is look at wind vane steering systems. They steer just fine (with a fair bit of fussing) off deck level winds. Most people who would be happy with that level of steering performance would satisfied with a compass course autopilot, but everybody runs their boats differently, and in different places and conditions.

[Dockhead]

Originally Posted by CatLove

Another option, perhaps as bad as on the bimini would be in the front of the bow on a bowsprit:

That sensor is solely for measuring shear. The main sensor is at the masttop.

[Dockhead]

Originally Posted by alanfw

In my context, the interest is direction of wind as it's used by the tiller pilot.
Wind speed may be interesting, but in terms of boat management, feel and vision is sufficient.

Don't waste your time. The airflow is highly disturbed there; you will get false and inconsistent readings.


If you want to reduce installation hassle at the masttop, try a wireless one.


Good wind data is really important to have good autopilot performance in wind steer. Particularly downwind. For that you want the wind instrument to be in the best position possible, and preferably as high as possible to reduce upwash distortions.