Yaw damping on windvanes

[RobbieH]

Hi,

I have a Windpilot Pacific on my Dufour Arpege. I've been using it on and off for 5-^ years now on annual cruises around the Nsea, Channel and Baltic. We were sailing back along the Dutch coast recently, shallow water, beam swell of about 1.5-2 meters and about 25 knots of wind just abaft the beam, maybe 30 knots in gusts. Hi clewed jib (clew around about level with fwd lowers) and 2 reefs in the main.

The boat was fine but there was a lot of yawing, coming over the crest of the swell the boat would head up and then fall off as the windvane did its thing. Tendency to overcorrect downwind and then in the next gust/crest she would head up again.

It didn't seem very efficient compared to handsteering. When hand steering I didn't notice objectionable amounts of weather helm.

In the Windpilot blurb they talk about "automatic yaw damping using a 360 degree bevel gear". I don't understand how/why this performs yaw damping can someone enlighten me?

Does adjusting the windvane sensor (the plywood vane) tilt angle help with this? Tilting it further back so it takes less input from the wind?

I won't be able to play with this until next season but if anyone has any ideas how to reduce the yawing ("corkscrewing" might be another good word for it) I'd welcome some input.

 

[KellysEye]

>Tendency to overcorrect downwind and then in the next gust/crest she would head up again.

That indicates the sails aren't balanced to give a neutral helm.

 

[RobbieH]

Maybe - it's the first time I'd used that new jib. Perhaps I'll have to pay more attention to getting a balanced helm (although it felt OK when I was steering). I wouldn't have expected to go to three reefs in those conditions broad reaching.

 

[Daydream believer]

I do not believe it is sail balance. On my aeries the power is such that at 6Kts a grown man cannot hold the control line for very long until he became overpowered- so there is plenty of power there ( The current manufacturer of the Aeries agrees with me on this when I discussed sail balance with him) Obviously better balance helps but is difficult with quartering seas & winds

What happens is that the boat accelerates down the wave & the immersed hull shape changes upsetting hull balance. ( as opposed to sail balance)As the boat accelerates there is less wind acting on the vane. I expect that reducing vane power by angling it down would not help. it would if the boat was over reacting but in this case the reaction comes too late after the boat has rounded, or begun rounding
I was in a similar situation in my 31 ft boat this year and my raymarine EVO 100 autopilot could not cope. ( kept cutting out & loosing calibration once 90 degrees of course which can be a bit startling to say the least) I tried hand steering but could not control the power on the tiller. The Aeries saved the day because it always got the boat back on course & did not wander as much as me or the autopilot.
I have tried various remedies- larger vanes, V shaped vanes, fabric vanes vanes with trim tabs etc. I found that a larger than recommended ply vane covered each side for 50% of the area with epoxy GRP matt to stiffen up & avoid flex & twist, was the best. ( It keeps the ply much stiffer & makes a surprising difference to ply only vanes)
I would not worry about the course variation as long as one is going generally where one wants to. But experimenting with vanes as I have over the last 10 years does help. That is how I found out about GRP faced vanes working best

 

[30boat]

I do not believe it is sail balance. On my aeries the power is such that at 6Kts a grown man cannot hold the control line for very long until he became overpowered- so there is plenty of power there ( The current manufacturer of the Aeries agrees with me on this when I discussed sail balance with him) Obviously better balance helps but is difficult with quartering seas & winds

What happens is that the boat accelerates down the wave & the immersed hull shape changes upsetting hull balance. ( as opposed to sail balance)As the boat accelerates there is less wind acting on the vane. I expect that reducing vane power by angling it down would not help. it would if the boat was over reacting but in this case the reaction comes too late after the boat has rounded, or begun rounding
I was in a similar situation in my 31 ft boat this year and my raymarine EVO 100 autopilot could not cope. ( kept cutting out & loosing calibration once 90 degrees of course which can be a bit startling to say the least) I tried hand steering but could not control the power on the tiller. The Aeries saved the day because it always got the boat back on course & did not wander as much as me or the autopilot.
I have tried various remedies- larger vanes, V shaped vanes, fabric vanes vanes with trim tabs etc. I found that a larger than recommended ply vane covered each side for 50% of the area with epoxy GRP matt to stiffen up & avoid flex & twist, was the best. ( It keeps the ply much stiffer & makes a surprising difference to ply only vanes)
I would not worry about the course variation as long as one is going generally where one wants to. But experimenting with vanes as I have over the last 10 years does help. That is how I found out about GRP faced vanes working best

Mmmm,there's a nice project for my Monitor...

 

[macd]

I do not believe it is sail balance....

A sensible analysis, I think, Daydream. You're certainly right that the power in a servo-pendulum system can overcome sail imbalance (I used to invite hefty crew to use every fibre to pull the tiller against it: they couldn't, even a bit). That said, reasonable balance is certainly desirable and advocated by all makers of wind vane systems. Equally your notion of acceleration through semi-surfing, which roughly equates to steering through gusts, sounds spot-on.

Regarding yaw in general on servo-pendulum systens, the two common design features designed to reduce it are the bevel gear RobbieH describes and the 15-degrees-or-so angle of supposedly "horizontal" wind vanes. I've always presumed that the yaw these reduced was on more of an inherent and macro level, rather than the (somewhat) longer-term feature whoch troubles Robbie. As you say, that can be ameliorated but, on some points of sail/sea conditions, ultimately has to be lived with.

 

[RobbieH]

I do not believe it is sail balance. On my aeries the power is such that at 6Kts a grown man cannot hold the control line for very long until he became overpowered- so there is plenty of power there ( The current manufacturer of the Aeries agrees with me on this when I discussed sail balance with him) Obviously better balance helps but is difficult with quartering seas & winds

What happens is that the boat accelerates down the wave & the immersed hull shape changes upsetting hull balance. ( as opposed to sail balance)As the boat accelerates there is less wind acting on the vane. I expect that reducing vane power by angling it down would not help. it would if the boat was over reacting but in this case the reaction comes too late after the boat has rounded, or begun rounding
I was in a similar situation in my 31 ft boat this year and my raymarine EVO 100 autopilot could not cope. ( kept cutting out & loosing calibration once 90 degrees of course which can be a bit startling to say the least) I tried hand steering but could not control the power on the tiller. The Aeries saved the day because it always got the boat back on course & did not wander as much as me or the autopilot.
I have tried various remedies- larger vanes, V shaped vanes, fabric vanes vanes with trim tabs etc. I found that a larger than recommended ply vane covered each side for 50% of the area with epoxy GRP matt to stiffen up & avoid flex & twist, was the best. ( It keeps the ply much stiffer & makes a surprising difference to ply only vanes)
I would not worry about the course variation as long as one is going generally where one wants to. But experimenting with vanes as I have over the last 10 years does help. That is how I found out about GRP faced vanes working best

Interesting, I was thinking about a bigger vane in the context of lighter/aft winds but had not consiered it for stronger winds too. I take your point about hull imbalance but the Arpege is not noted for having a particularly unbalanced hull, it loads up the tiller quite progressively. What boat/hull_shape is your 31 footer?

I am also thinking about connecting up my AH ST2000+ to drive the sensor vane in wind trim mode. I wonder if the gusts are reaching the sails (particularly the top half of the sails) before they are getting to the windvane and/or the windvane is being blanketed by the swell in the trough and only picking up the wind as it crests the swell. Perhaps if the wind input to the system is coming from the top of the mast instead of the transom there would be less of a lag and hence the self-steering would react more quickly or more in phase with the wind. Might be interesting to look at the NMEA from the wind instruments and contrast that visually with what the windvane sensor is doing to get a feel for that.

Does anyone know how Mini-transats drive their autopilots? Does the input come from a fluxgate compass or wind instrumentation? And if wind instruments is it from top of mast or something mounted somewhere else? They are fast boats, subject to rounding up in gusts (I suppose given hull shape) and must suffer considerable variations in apparent wind force/direction when on the edge of planing in swells. Perhaps it is a balance between keeping sail trim and keeping a course (can't be too much use to a racer to be always maintaining maximum speed but in the wrong direction for most of the time).

 

[RobbieH]

Regarding yaw in general on servo-pendulum systens, the two common design features designed to reduce it are the bevel gear RobbieH describes and the 15-degrees-or-so angle of supposedly "horizontal" wind vanes. I've always presumed that the yaw these reduced was on more of an inherent and macro level, rather than the (somewhat) longer-term feature whoch troubles Robbie. As you say, that can be ameliorated but, on some points of sail/sea conditions, ultimately has to be lived with.

That was part of my question - I'm not visualising how the bevel reduction (2:1) gear reduces yaw. Can anyone explain that?

And if a 15 degree angle to the windvane reduces yaw for some reason (in certain conditions) would a 20 degree angle be better in other conditions? Or a 10 degree angle, or whatever angle? What is magic about 15 degrees and does it vary according to conditions? I seem to remember suggestions to alter the angle according to wind strength to reduce input in strong winds (increasing angle, less upright) and increase input in light winds (more upright) ...

So many variables, so little time ...

 

[GHA]

Part of it might be the vane reacting as the apparent wind moves back a bit in the gusts. My Aries can be very sensitive with wind over the quarter, one click making quite a big change in course as the apparent wind changes.

 

[KellysEye]

>I do not believe it is sail balance. On my aeries the power is such that at 6Kts a grown man cannot hold the control line for very long until he became overpowered- so there is plenty of power there ( The current manufacturer of the Aeries agrees with me on this when I discussed sail balance with him) Obviously better balance helps but is difficult with quartering seas & winds

Firstly the OP hasn't got an Aries, second he hasn't got a Hydrovane either but if I balanced the sails thenour boat would steer straight in any conditions upwind, downwind or reaching. By definition if the the sails are unbalanced and trying to turn the boat then a wind vane can't cope, even reefed sails have a huge amount of more power than the relatively tiny sail on a windvane.

 

[RobbieH]

It's definitely true that for beam or abaft courses very little change in vane angle makes a lot of difference in course. Sometimes a bit of a knife edge to get it right.

Movement of apparent wind might be an argument for using the AH 2000ST+. There is some kind of algorithm in Wind Trim mode which averages/damps the wind inputs to smooth wind direction variations. AFAIK it's not variable and I don't know if it would be too much or too little damping for the input to the self-steering.

I suppose I could put a processing/logging box between the wind instrument and the autohelm into which I could program my own algorithms for smoothing wind variations and make it variable that way. So the AH algorithms would only see the smoothed NMEA data and presumably would not kick in. That would work if the AH wind trim algorithm damped less than the windvane needed - it would not be beneficial if the AH was too aggressive with its damping.

If I fed the processing box with heading data from the fluxgate, log speed and VMG too it could perhaps be smarter about automating the tradeoff between course, sail trim and speed. Or I could buy a much more expensive autopilot that allowed control of some variables - not sure how I would link that to the windvane and I don't think I want to go all electric for the selfsteering.

Regardless of the alteration of data passed on to the AH data logging might be an interesting way to learn more about the performance and handling of the boat by graphing and reviewing the data at a later date. For me, shorthanded or solo it's usually more a case of getting from AtoB without incident rather than squeezing more performance. Post trip review/analysis in the comfort of an armchair might be easier. A good racing helm/trimmer could probably come on the boat and tell me what was happening - unfortunately I don't have that background.

Back to earth - something to muse about when scraping anti-foul this winter

 

[RobbieH]

>I do not believe it is sail balance. On my aeries the power is such that at 6Kts a grown man cannot hold the control line for very long until he became overpowered- so there is plenty of power there ( The current manufacturer of the Aeries agrees with me on this when I discussed sail balance with him) Obviously better balance helps but is difficult with quartering seas & winds

Firstly the OP hasn't got an Aries, second he hasn't got a Hydrovane either but if I balanced the sails thenour boat would steer straight in any conditions upwind, downwind or reaching. By definition if the the sails are unbalanced and trying to turn the boat then a wind vane can't cope, even reefed sails have a huge amount of more power than the relatively tiny sail on a windvane.

Can you have a situation where the sails are balanced but the hull form is unbalanced? Or vice-versa? I agree that (for example) leech tension on my main makes a big difference to whether the windvane can cope or not. But is that because the sails are turning the boat or the boat is heeling more than it should (in gusts) and then the hullform is causing the boat to luff? Meaning I need to trim the sails to avoid heeling in gusts as much as reasonable/possible (short of taking down all sail!)

Seems to me that sail balance is dynamic. When we are sailing the boat at its limit on flat water and a puff comes we typically luff a bit to the new apparent wind, load up the helm somewhat and also drop the traveller a bit to spill a bit of wind if the boat feels like she is on the edge. In extremis I would let some mainsheet out. But when the puff/gust dies the perfect trim will eventually settle back where it was before (after a bear away).

So sail trim (leach/sheet tension, mainsail area), and hence balance, under windvane must always be conservative (compared to handsteering) when the wind is gusting at all (if you want to avoid luffing and bearing away) because you don't have that dynamic control of the sails. You need the sails to remain relatively balanced over a wider range of windspeeds than when handsteering and so you sacrifice extracting some power from the wind for an easy life. I was reading a recent report of the end of one of the solo Atlantic races and somone was handsteering for the last 40 hours because he could drive the boat better (even with the sophisticated autopilot system that was fitted). I don't mind losing some sailing efficiency for an easy life but, if that's what needed, then I'm struggling to find the sweet spot for sail trim. I can trim OK for gusts when hand steering but I can't trim well for the windvane.

@Kellys-Eye - Do you trim the sails differently when handsteering vs. windvane and if so how? And what type of boat (hullform/size are we talking about?)

Thinking about the effect of the boat speeding up on the downhill swell slope making the apparent wind draw aft and causing a luff. Not sure my heavily laden cruising boat was doing much surfing and the swell was beam on so there wasn't much of a downhill slope.

 

[macd]

That was part of my question - I'm not visualising how the bevel reduction (2:1) gear reduces yaw. Can anyone explain that?

And if a 15 degree angle to the windvane reduces yaw for some reason (in certain conditions) would a 20 degree angle be better in other conditions? Or a 10 degree angle, or whatever angle? What is magic about 15 degrees and does it vary according to conditions? I seem to remember suggestions to alter the angle according to wind strength to reduce input in strong winds (increasing angle, less upright) and increase input in light winds (more upright) ...

So many variables, so little time ...

Sorry, you misunderstand me. The 15 degree angle is built in to the hardware: it's the angle of the pivot on which the vane rides. I5 degrees has been arrived at over the years as the value that best works. It is not adjustable on any servo system so far as I know.

Yes, the 'attack angle' of the vane itself is adjustable. Forthmann explains how best to use this.

 

[RobbieH]

Sorry, you misunderstand me. The 15 degree angle is built in to the hardware: it's the angle of the pivot on which the vane rides. I5 degrees has been arrived at over the years as the value that best works. It is not adjustable on any servo system so far as I know.

Yes, the 'attack angle' of the vane itself is adjustable. Forthmann explains how best to use this.

OK, thanks for the clarification - I'll review what he says about attack angle.

 

[Daydream believer]

Firstly the OP hasn't got an Aries, second he hasn't got a Hydrovane either but if I balanced the sails thenour boat would steer straight in any conditions upwind, downwind or reaching. By definition if the the sails are unbalanced and trying to turn the boat then a wind vane can't cope, even reefed sails have a huge amount of more power than the relatively tiny sail on a windvane.

I was fully aware of that but the principles of how they work are similar. I can only describe my experiences to the Op so he can evaluate the relevant parts for his own use

i have a tiller steered Hanse 311 which is an AWB with short fin keel. It is very directionally unstable, There is no way I could balance the sails with the wind coming over the stern quarter without rigging some sort of back winded sail or perhaps dropping the main or booming a foresail well forward & then it may well curve a lot & the C of E would swing from side to side unbalancing the boat( a normally poled foresail would keep collapsing at that angle) .

I would suspect that most boats will round up to varying degrees in the situation described by the OP. I an surprised that ( assuming monohull sail boat) your boat will sail on its own in a quartering sea in heavy wind with a big swell coming over the quarter unless you are using foresails only, coupled with some sort of steering system. Perhaps you would like to tell us what the boat is. My last 2 boats were long keeled & they both rounded up fairly quickly. Clearly sail balance helps steering, but it is not necessary to totally balance the sails as some seem to think.

The difference between vane size & sail area you mention is largely irrelevant. the vane works a steering oar which works the steering. If what you were saying is correct then boats from as little as 25 ft to 45 ft plus would not be able to operate on similar principles. On the Aeries the vane is generally supplied with the same size for my boat as it is for a 45 ft boat. I bought my Aeries because the helm on my boat was too heavy for my wife to helm for more than 20 minutes. In fact she finally refused to helm ( so now I leave her at home!!) It also overpowered the Simrad TP 32 sometimes

I am not the only forumite posting in this thread that mentions the power of the steering oar once the boat is moving at a reasonable speed & this applies to many types of steering system using a steering oar

The 15/20 degree rake that some have mentioned came about with the transition from vertical axis vanes to horizontal axis vanes
With vertical axis there is a dead band area before they develop full power. Horizontal axis tends to be a bit " lively" and over react. Experimentation has found that a mixture of the 2 ( ie 15/20 degrees of rake) is the best mix

People have been developing these systems over years and millions of miles so one can be fairly certain that within this style of design most manufacturers have got it fairly right

the Hydrovane works on a different principle & is not the same as that used by the OP's vane gear

 

[30boat]

My Monitor is a very powerful windvane but the makers still advise that proper sail balance is essencial.I've learnt that reducing the mainsail often helps a lot with directional stability.The Fulmar is very well balanced but the Monitor can be fussy especially in the conditions the OP described.

 

[Christian Williams]

Sail trim for neutral helm, I believe, is the most ignored factor. And reducing sail area.

As was suggested earlier, if the boat is rolling, or surfing off angled wave trains, or just heeling in gusts, then the hull form makes her head up -- and a wind vane can only respond, not anticipate.

So it really helps a vane to reduce those effects. Alas, many of us feel a failure if the boat is not at hull speed all the time. For that, a racing helmsman, not a mechanical gizmo.

Here is my Sailomat on a 32-footer en route to Hawaii, dead downwind for weeks:

https://www.youtube.com/watch?v=_gEJ3RJYiYc

 

[fishermantwo]

The 15 degree rake is there to reduce the power of the vane as the vane gets to the maximum of its range. By the time the vane is leaning over on it's stops the boat has already responded so less power is required and this reduces the tendency to oversteer. Straight horizontal vanes have the same power over the whole arc and will oversteer badly.

I have a home built SS system similar to a Monitor. I added a spoiler trim to the rear edge of the wind vane to add some drag to make it less sensitive. I also rake it back in fresh winds to reduce power. My yacht is a half tonner and is easily steered and I can reef the sails easily but I have found it's the weather helm that has to be allowed for especially sailing downwind. Upwind it virtually sails herself like most yachts and I use a twin jam cleat system on the end of my tiller for the control lines. If I was just going upwind the lines go straight to the cleats. I have two other turning points on the tiller for the control lines and if I was to spend some time going straight down wind I use the shortest turning point which gives me the quickest reaction time but less leverage. By having separate jam cleats I can make adjustments for weather helm. If your sailing on a broad reach and with a few waves as the breeze alters in strenght you are going to have to alter the amount of weather helm you have preset when you connected your vane.
This is a short video of my yacht reaching in about 15 knots of wind. My boat is the same size as an Arpege.
https://www.youtube.com/watch?v=FZmYCnB1wRI
This is more about my vane.
https://www.youtube.com/watch?v=isw529SdN8s
In this video you can see that I use the centre turning point at the start and later the lines go straight to the jam cleats. The principals and dimensions and ratios are identical to yours.
I would suggest perusing this site. I'm Ramona there.
http://www.cruisenews.net/forum/viewforum.php?f=62&sid=ea5cc8751963d62c5533a3ff40490751

 

[KellysEye]

>I do not believe it is sail balance.

Having sailed over 10,000nm with a Hydrovane I can assure the disbelievers that if you don't balance the sails to get a neutral helm and lock the helm so the rudder can't move then the wind vane won't steer straight. Two boats I met in Portugal who had crossed Biscay were complaining that their wind vanes weren't steering straight. I went out sailing with them balanced the sails to get a neutral helm, locked the helm and both windvanes steered straight. They were both very grateful for the lesson.

 

[macd]

>I do not believe it is sail balance.

Having sailed over 10,000nm with a Hydrovane...

Groundhog Day?
You already took issue with that very quote from Daydream Believer...last September. He replied, argueing his position...also last September. If you're going to keep doing this periodically, it might be a kindness to tell him so he can arrange is social life to suit