Wind direction indicator on rotating mast

[baldbaby2000]

I'll be getting an 26M, which has a rotating mast. Does anyone know of an electronic wind direction indicator that will work on a rotating mast? Wind speed shouldn't be a problem but it seems that for direction it would require an input from a sensor that measures the mast rotation in addition to the wind vane position. Or are there other suitable locations that could be used, such as a fixed position above the bow pulpit?

[Paul S]

I'll be getting an 26M, which has a rotating mast. Does anyone know of an electronic wind direction indicator that will work on a rotating mast? Wind speed shouldn't be a problem but it seems that for direction it would require an input from a sensor that measures the mast rotation in addition to the wind vane position. Or are there other suitable locations that could be used, such as a fixed position above the bow pulpit?

Not sure how well it would work on the mast. You might be better off on the mast support at the stern (if you get a late 04+). It is out of the way. Low enough that you can remove it for trailering easily

[Tom Spohn]

I guess I'm missing something. Why wouldn't the indicator work OK on the rotating mast?

[Duane Dunn, Allegro]

A vane will still point to the wind fine, but any fixed portion such as the tabs that show the sailing angle would be wrong as the mast rotates since they would be rotating too.

The same would be true of real wind instruments that show the wind direction off the boat. The centerline of the mast doesn't just point one direction so the instrument can't be indexed correctly. You could be close hauled but with the mast rotated the instrument would think the wind is coming from the nose. You will get unrealisticly low tacking angles as the mast rotates.

[Kevin]

I don't know how large the sensors are for the wind indicators but maybe you could mount them on the spreaders. While the M mast rotates the spreaders are in a fixed position, held by the shrouds.

[baldbaby2000]

I suspect that the spreader location would be influenced too much by the headsail. On the stern it might have distorted readings too. Although if one can sail based on these effects, maybe it would still be useful.

[Frank C]

I purchased an ST60 "open box" wind instrument from West Marine. The advantage was price, disadvantage was I had only one week of return privileges, during which I had to install and test it. Mounting the wind tranducer on the bow pulpit was the expedient way to test it.

It worked fine from there, and it's clearly forward of the influence of sails. The obvious drawbacks are that it's very prone to damage and reads wind direction closer to the surface than desireable. On balance, while I enjoy the ST60, I'd recommend that you go with the ST40 (about half the cost of the ST60), and mount it at the bow pulpit. The ducer can be easily removed from its wiring/mount, so you can protect it when working on the bow, docking or anchoring.

[Chip Hindes]

it's clearly forward of the influence of sails.

The wind direction is affected to some degree well forward of the sails on any tack. Particualrly so if the sails aren't trimmed properly. On a broad reach or run I'm thinking a bow mounted indicator will be useless.

An interesting problem.

Question: What is the angle of rotation, and does the mast assume any of an infinite number of angles, or does it tend to bang to one side or the other and stay there? If the latter, it might be possible to compensate in software. No doubt requiring serious help from the manufacturer of the instrument.

Don't some pretty serious big boats have rotating masts? Looks like there could be a market for unit with a second sensor (mounted to the deck, spreaders or something else stationary) which measures mast rotation, then electronically or through software sums the two for a "true" reading.

[craiglaforce]

Simple. I assume the true wind sensor works in concert with the fluxgate compass. Just mount the compass on the rotating mast as well. (Then the mast becomes the boat in essence). You will need a second compass for boat heading inputs.

You guys and your electronic toys! Tie some yarn on the shrouds and go sailing!

[Frank C]

Simple. I assume the true wind sensor works in concert with the fluxgate compass. Just mount the compass on the rotating mast as well.

Actually, Craig, not quite so simple. The wind indicators show apparent, not true wind. They are reading deviation from their centerline position ('relative' wind angle). The only way a wind indicator can reflect true wind angle (and true wind speed) is with interface to a GPS. I find it intriguing that they include the algorithms to deduce true wind speed, but I've never bothered to connect to the GPS.

Chip,
True indeed for anything from beam reach or lower. It's an amazing instrument, well worthwhile, IMO, even without the downwind angles.Guess I overlooked such a basic factor (downwind blanketing) because 90% of the wind instrument's benefit, for me, is the upwind info.

I suppose your point might be that the wind "piles up" afore the luff, especially when the sail is poorly trimmed? Seems to me that testing for that effect would be NON-trivial. Mount at the bow, allow the mast to pivot, measure your pointing and wind speeds for a weekend. Next, put it at the masthead, lock the mast pivot, measure your pointing again. Now, are the deviations due to the mast pivoting or measurement errors at the bow? The other big problem ... running that 5-wire cable to the masthead of a 26M is non-trivial, too.

Since the instrument is primarily for judging relative changes, I'm not sure that impact would be crippling for upwind work.

[craiglaforce]

OK Frank, keep me honest.

The wind direction indicator measures apparent wind direction. By mounting the compass on the mast, the index on the windvane will always have the same orientation to the fluxgate compass and should solve the problem. Of course whether the mast rotates or is stationary, the true wind direction is calculated from apparent wind direction, apparent wind velocity, and boat speed and course over ground.

I'm asuming that the software already does the parts I didn't describe in detail.

Maybe I oversimplified it in my previous post.

[Frank C]

OK Frank, keep me honest.

The wind direction indicator measures apparent wind direction. By mounting the compass on the mast, the index on the windvane will always have the same orientation to the fluxgate compass and should solve the problem. ....

Actually Craig, I suspect that we're on different pages.

The wind instrument is delivered without compass, and it does not show any compass headings. Instead, the 'ducer is just an indicator which is "zero-referenced" on the mast's centerline during installation. Hopefully the mast centerline remains on the hull's centerline, right?

The real objective is to pin "zero" to the centerline of the hull. The display is simply a rotating needle that constantly points to "zero" while the hull rotates beneath it. Since the centerline of the 26M's mast does not remain on the hull's centerline, the 'ducer will clearly remain on the mast's centerline, therefore failing to reflect the relative angle of the hull versus apparent wind.

• IDIOT'S EDIT: Sorry - I misspoke just above. The rotating needle constantly points to the apparent wind. The Zero point represents the bow (on the dial face), which rotates 'beneath' the wind pointer. As the bow (Zero) drifts to port, the wind needle veers into the green "starboard" sector, showing apparent wind coming across the stb forequarter ... and so on. However, the mechanism remains a "relative pointer" to the wind, not a compass heading.

I suppose the simple solution is to add another 'ducer somewhere on the hull, and measure (subtractively?) the changes in zero-position between those indicators. Easy, but probably costly, eh?

[craiglaforce]

Sorry, I had a wrong picture in my mind of the equipment it comes with.

[Harry van der Meer]

On balance, while I enjoy the ST60, I'd recommend that you go with the ST40 (about half the cost of the ST60)

Frank, why would you recommend the ST40 over the ST60? What is the difference?

[normo]

Many multihulls like the Corsair F24,28,31,etc have rotating masts. They have an active racing program so they surely have apparent wind instrumentation and know all the specifics.

Look at the Finish Line web site http://www.fboats.com/Corsair/NavigationBar.htm and call them. They are located in my home town. Steve Marsh is the owner.