Question?
When sailing upwind and the winds are light where should the traveler be positioned?
Thanks
When sailing upwind and the winds are light where should the traveler be positioned?
Thanks
Traveler Position In Light Wind
- Thread starter Ducati
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In accordance with how the tell tales are flying on the mainsail.
Typically with the vang loosened and the traveller pulled slightly to the weather side (depending how heavy the boom is) so that all the lee-side tell tales are streaming straight back.
Also, the main sail somewhat flattened so to avoid separation stalls @ midcord (because of too much draft).
Typically with the vang loosened and the traveller pulled slightly to the weather side (depending how heavy the boom is) so that all the lee-side tell tales are streaming straight back.
Also, the main sail somewhat flattened so to avoid separation stalls @ midcord (because of too much draft).
Separation stall is when there is not enough energy in the air for the flow to stay 'attached' to the curved foil. It can also occur when the amount of draft (curvature) is too great and the flow doesnt have enough energy to stay 'attached'.
On a practical basis, separation stalls occur regularly on sails in light winds .... and you can indirectly see them when the leeside tell tales are 'hanging straight down' instead of flowing straight back. The cause is usually due to the sail having too much draft for the light wind conditions; and, thats why FLAT sails usually work the best in very light winds. Its all by closely watching the action of the tell tales.
Two kinds of 'stalls': stagnation stalls, separation stalls. Sailing books usually only deal with stagnation stalls.
On a practical basis, separation stalls occur regularly on sails in light winds .... and you can indirectly see them when the leeside tell tales are 'hanging straight down' instead of flowing straight back. The cause is usually due to the sail having too much draft for the light wind conditions; and, thats why FLAT sails usually work the best in very light winds. Its all by closely watching the action of the tell tales.
Two kinds of 'stalls': stagnation stalls, separation stalls. Sailing books usually only deal with stagnation stalls.
Flat Sails In Light Wind?
Typically with the vang loosened and the traveller pulled slightly to the weather side (depending how heavy the boom is) so that all the lee-side tell tales are streaming straight back.
Also, the main sail somewhat flattened so to avoid separation stalls @ midcord (because of too much draft)
Sorry I think that you are incorrect regarding flat sails in light winds.
In light winds we have always put some curve in the sails.
We also put the weight to the low side...when racing.
Comments?
Typically with the vang loosened and the traveller pulled slightly to the weather side (depending how heavy the boom is) so that all the lee-side tell tales are streaming straight back.
Also, the main sail somewhat flattened so to avoid separation stalls @ midcord (because of too much draft)
Sorry I think that you are incorrect regarding flat sails in light winds.
In light winds we have always put some curve in the sails.
We also put the weight to the low side...when racing.
Comments?
Separation stalls are the bane of light wind sailing. Separation stalls are prevented by FLAT sails, not plywood-sheet-flat but flat enough to prevent the stall ....AND the larger the headsail the greater the propensity to develop a separation stall.
This may seem counterintuitive to the usual recommendations; but, if you overdraft by putting 'some extra curve' or increasing draft you will accelerate but wont attain the speed shape needed to *artificially increase the velocity of the apparent wind* .... and will be restrained in the 'slows'. Successful light wind racers are those who can artificially increase the apparent wind and keep it to the maximum.
Light wind racing needs different methods: accelerating by TRIM methods (footing off, etc.) and then attaining the highest speed possible .... to allow the *apparent wind* to get to and stay at its maximum. 'Rounded' sails (powered up) will prevent the speeds that maintain increasing apparent wind. Light wind racing needs a LOT of practice and data collection to develop such skills at shaping, so that youre always at optimum, etc.
The lighter weight boat (especially with a boat with a bendable mast) the better the effect of 'flatter' sails. What I dont say is artificially and blindly putting in a flat shape; but rather, starting with a 'flatter' shape and watching the tell tales to verify the effect and making changes in shape accordingly.
If you have enough crew, then of course you can change shape depending on whether you need to accelerate (during going into and out of a tack) or go into 'speed mode' while 'stretching out the legs' ... altering between rounded or flattened. Flat is for speed, rounded is for accelerating and you must be able to shift the gears between the two if you want to be a successful racing skipper or crew. Middle and end of the pack racers never seem to change the shape of their sails once the race starts ... the front of the pack racers always constantly do this ... as the wind etc. conditions change
I'd also add that in my experience for light wind racing, that a smaller headsail (again so that you dont wind up with a separation stall instability because of the large cord length) usually works better for upwind; changing to a % jib that doesnt allow an easy separation stall (usually a 'smaller' jib) during the pre-race 'tune up'.... then change/peel to a larger jib (or spinnaker) when coming back down when you get the benefit of larger sail area. All dependent on how the tell tales (and speedo/VMG) are working, or not.
Of course the accumulation of large amounts of data over time from settings, speeds, acceleration periods will give you the best initial settings - especially beneficial for light wind racing, etc.
"In light winds we have always put some curve in the sails.
............ when racing."
If youre not consistently placing high in the the fleet then maybe you should try the above when racing in 'light' conditions.
;-)
This may seem counterintuitive to the usual recommendations; but, if you overdraft by putting 'some extra curve' or increasing draft you will accelerate but wont attain the speed shape needed to *artificially increase the velocity of the apparent wind* .... and will be restrained in the 'slows'. Successful light wind racers are those who can artificially increase the apparent wind and keep it to the maximum.
Light wind racing needs different methods: accelerating by TRIM methods (footing off, etc.) and then attaining the highest speed possible .... to allow the *apparent wind* to get to and stay at its maximum. 'Rounded' sails (powered up) will prevent the speeds that maintain increasing apparent wind. Light wind racing needs a LOT of practice and data collection to develop such skills at shaping, so that youre always at optimum, etc.
The lighter weight boat (especially with a boat with a bendable mast) the better the effect of 'flatter' sails. What I dont say is artificially and blindly putting in a flat shape; but rather, starting with a 'flatter' shape and watching the tell tales to verify the effect and making changes in shape accordingly.
If you have enough crew, then of course you can change shape depending on whether you need to accelerate (during going into and out of a tack) or go into 'speed mode' while 'stretching out the legs' ... altering between rounded or flattened. Flat is for speed, rounded is for accelerating and you must be able to shift the gears between the two if you want to be a successful racing skipper or crew. Middle and end of the pack racers never seem to change the shape of their sails once the race starts ... the front of the pack racers always constantly do this ... as the wind etc. conditions change
I'd also add that in my experience for light wind racing, that a smaller headsail (again so that you dont wind up with a separation stall instability because of the large cord length) usually works better for upwind; changing to a % jib that doesnt allow an easy separation stall (usually a 'smaller' jib) during the pre-race 'tune up'.... then change/peel to a larger jib (or spinnaker) when coming back down when you get the benefit of larger sail area. All dependent on how the tell tales (and speedo/VMG) are working, or not.
Of course the accumulation of large amounts of data over time from settings, speeds, acceleration periods will give you the best initial settings - especially beneficial for light wind racing, etc.
"In light winds we have always put some curve in the sails.
............ when racing."
If youre not consistently placing high in the the fleet then maybe you should try the above when racing in 'light' conditions.
;-)
Very light wind - flat
Light - a little curve
Gaining - a bit more curve
Heavy wind - flat
It seems counter intuitive, but I learned by racing and then reading and rereading all of the Sail Trim books I could lay my hands on.
RichH is right.
It would also help to define wind speeds, not just my definitions, but that's a start.
I know of two (at least) sailmaikers in the NW that can and do correctly use "laminar flow" in sentences.
Do not buy any sails from those guys that do not understand what you are doing...
RichH
If I understand you correctly, you should power up your sails from a stall and as you pick up speed you need to flatten them out. Is that correct?
... and on a related point, I was hoping you might be able to explain something else I've noticed. I have a relatively light boat so it is very responsive. In light air I find that I have to keep my crew from moving about or else they tip the boat and spill my air. It also seems to me that if I induce an artificial heel by moving my crew to leeward, the boat picks up speed. Why does a little bit of heel speed up the boat? Or is this just my imagination?
THNX
r
If I understand you correctly, you should power up your sails from a stall and as you pick up speed you need to flatten them out. Is that correct?
... and on a related point, I was hoping you might be able to explain something else I've noticed. I have a relatively light boat so it is very responsive. In light air I find that I have to keep my crew from moving about or else they tip the boat and spill my air. It also seems to me that if I induce an artificial heel by moving my crew to leeward, the boat picks up speed. Why does a little bit of heel speed up the boat? Or is this just my imagination?
THNX
r
Power-up not from a stall but when you need to accelerate such as out of a tack, etc.
"In light air I find that I have to keep my crew from moving about or else they tip the boat and spill my air" ..... that 'shaking' by the crew is forcing the attached flow of air to 'separate' (destroys the smooth flowing 'boundary layer') from the sails --- a separation stall; ..... and it does take quite some time for the flow to re-attach properly. A sail with tooo much 'roundness'/draft will easily have the flow separate (stall) in light conditions.
Getting the crew to the leeside does two things:
1. it helps the sails take on or settle into their best 'aerodynamic shape'
2. On relatively flat-bottomed boats especially, it reduces the amount of surface area of the hull in contact with the water for less hull drag.
Examples: ILYA scows, skiffs, and the modern hybrid wide-beamed racing forms, etc. Some of the tunnel-hulled (bottom profile looks like a soft "w") boats will reduce the wetted surface are by ~2/3 when forced to heel to the leeside and can easily plane to windward.
I think its generally agreed that it's flat sails in very light air, and for just light air more camber. If there is separation of the air flow from the sail drag increases and reduces the driving force. The goal is to always have as much attached flow as possible and tell tails are the way to know what's happening.
Crew weight position is very important. And yes, you don't want a cloghopper prancing around the deck in light air. It's a speed killer. It shakes the attached flow right off the sail.
Leeward boat trim in light air works for me. I think because there is less bottom area in the water and so less drag. Also, the weight of the sails works to keep the sail shape and to not invert the sail which is what would happen with windward boat trim. The water line may be longer - at least in some boats - too.
Crew weight position is very important. And yes, you don't want a cloghopper prancing around the deck in light air. It's a speed killer. It shakes the attached flow right off the sail.
Leeward boat trim in light air works for me. I think because there is less bottom area in the water and so less drag. Also, the weight of the sails works to keep the sail shape and to not invert the sail which is what would happen with windward boat trim. The water line may be longer - at least in some boats - too.
Sailing in light air is difficult to do well. In ultra light air (1 to 3kts) the sails need to be as flat as they can be. The boat heeled over with crew on the leeward rail and movement kept to a minimum. Sailing to weather in ultra light air the boom should be centered but cracking off on the helm will be necessary to keep the boat moving. You may need to sail 10 degrees lower than normal to maintain your best VMG.
As the breeze builds the curve in the sail is increased to build power because the laminar flow can stay attached further back on the sail. There comes a point as the breeze continues to build that flattening the sail starts again. This time it is to control heeling and weather helm. The flattening continues until the boat becomes overwhelmed with too much power and the sails have reached their trim limit. At this point it is time for a reef.
As the breeze builds the curve in the sail is increased to build power because the laminar flow can stay attached further back on the sail. There comes a point as the breeze continues to build that flattening the sail starts again. This time it is to control heeling and weather helm. The flattening continues until the boat becomes overwhelmed with too much power and the sails have reached their trim limit. At this point it is time for a reef.
Thanks Rich Shemander and Alan:
That all makes perfect sense. I guess I figured out what worked but did not understand why. I learned to sail on a sloop rigged dingy and I would just mess about until I was sailing faster but did not really understand what was happening to the sail.
So now you have me thinking about the "grip" of the wind on the sail. And how does the quality of the sail cloth affect the "grip".
Tell me if this thinking makes sense. The leeward air has a longer distance to travel (Bernoulli's Principle), and in light air if the "drag" on the leeward side air is too much, the wind flow becomes turbulent ( = separation). So to my thinking a smoother sail cloth would have less of a tenancy to undergo separation than one that is rougher as there would be less drag on the wind and it could "keep up" with the wind on the windward side. If my thinking is correct in this regards then some sort of treatments (like wax or scotch guard) might make your sail perform better in light air by reducing the drag on the wind.
Am I thinking about this correctly?
r
That all makes perfect sense. I guess I figured out what worked but did not understand why. I learned to sail on a sloop rigged dingy and I would just mess about until I was sailing faster but did not really understand what was happening to the sail.
So now you have me thinking about the "grip" of the wind on the sail. And how does the quality of the sail cloth affect the "grip".
Tell me if this thinking makes sense. The leeward air has a longer distance to travel (Bernoulli's Principle), and in light air if the "drag" on the leeward side air is too much, the wind flow becomes turbulent ( = separation). So to my thinking a smoother sail cloth would have less of a tenancy to undergo separation than one that is rougher as there would be less drag on the wind and it could "keep up" with the wind on the windward side. If my thinking is correct in this regards then some sort of treatments (like wax or scotch guard) might make your sail perform better in light air by reducing the drag on the wind.
Am I thinking about this correctly?
r
having a rigid vang (or boom kicker) that actively lifts the boom up also helps sail shape in light air, as it will hold the boom up so that you are not relying on the wind to apply pressure against the sail and lift the boom, and the weight of the boom is not ruining your sail shape.
Of course this could also be done without a rigid vang using the topping lift, but since on most boats vang control is much more accessible and easier to control than the topping lift, especially for frequent changes, it will often be skipped over as a result of it being "too much work"
Of course this could also be done without a rigid vang using the topping lift, but since on most boats vang control is much more accessible and easier to control than the topping lift, especially for frequent changes, it will often be skipped over as a result of it being "too much work"
I have used a company from NH that washes your sails and will also coat them with a teflon like spray. Because of the "lubricant"the sails roll tighter, specially in mast furling, and also increases performance because the material is smoother.
When sailing in very light air, you will also want to move the crew weight forward and get that fat stern out of the water. This will also create a little weather helm and help the driver to get a better feel and not move the rudder so much.
If a power boats goes by, have the crew flatten them selves on deck, also send crew below to sit on the lower side.
The largest and only headsail I use on my J-36 and on my prior Soverel 27 has been 125% cross cut dacron. Won the Rolex regatta 5 times. Both are with roller furlers.
When sailing in very light air, you will also want to move the crew weight forward and get that fat stern out of the water. This will also create a little weather helm and help the driver to get a better feel and not move the rudder so much.
If a power boats goes by, have the crew flatten them selves on deck, also send crew below to sit on the lower side.
The largest and only headsail I use on my J-36 and on my prior Soverel 27 has been 125% cross cut dacron. Won the Rolex regatta 5 times. Both are with roller furlers.
While I think this a good idea, and there are certainly no draw backs,
there does not seem to be a consensus among racing sailors regarding
the use of tell tales on mainsails, other than on the leech. On multihulls
with rotating masts, tell tales near the position of max camber are essential.
But I do not think they have proven to be remarkably effective on monohulls,
otherwise every boat racing would be using them and that does not appear
to be the case.
The answer to the origional query is slightly to windward, as to how far to
windward it depends on many factors ie... solid vang, sea state, foils etc.
"
**** Sails have virtually NO thickness, therefore this premise is totally wrong. Most of what you learned in USA high schools about wings and application of "Bernoulli" to foils is totally wrong. For a 'mildly' technical article of how sails generate lift, go to: http://www.arvelgentry.com/techs/Origins_of_Lift.pdf
**** Actually the smoothness of the sail promotes better of whats called a 'stable boundary layer' a regime of essentially NO flow very close to the sail material. Rough surfaces promote an unstable boundary layer.
Even the Wright Brothers would have projectile-barfed if they had to attend and listen to a USA high school explanation of how a wing works .... as they found out & proved 'otherwise' in the early 1900s !!!!!!!
;-)
.
**** Sails have virtually NO thickness, therefore this premise is totally wrong. Most of what you learned in USA high schools about wings and application of "Bernoulli" to foils is totally wrong. For a 'mildly' technical article of how sails generate lift, go to: http://www.arvelgentry.com/techs/Origins_of_Lift.pdf
**** Wrong/erroneous premise again, (damn those stupid high school teachers and their idiot nonsense-science curriculums) .... Refer to the above website and see how the air flow is divided from what is called the 'stagnation point' which on a two dimensional shape such as a sail, the stagnation point is ON ('down under') the windward side of the sail. Air flow will stay attached if there is enough 'energy' in the air flow to do so.
**** Actually the smoothness of the sail promotes better of whats called a 'stable boundary layer' a regime of essentially NO flow very close to the sail material. Rough surfaces promote an unstable boundary layer.
Even the Wright Brothers would have projectile-barfed if they had to attend and listen to a USA high school explanation of how a wing works .... as they found out & proved 'otherwise' in the early 1900s !!!!!!!
;-)
Thanks for the website Rich
In reading the site it states..
"The circulation flow field causes a
large amount of air to flow on the top (lee side) of the airfoil.
The same amount of air is flowing between each pair of
streamlines. The speed of the flow increases in areas where the
streamlines get closer together such as near the leading edge of
the airfoil. Higher speeds mean lower pressures. Where the
streamlines get farther apart such as on the lower surface, the
flow slows down and the pressures get higher. Lower pressures
on top and higher pressures on the bottom mean that the airfoil
now has lift."
I believe that is what I said when I stated that the air has farther to flow on the leeward side. And in order to catch up with the windward side air it must travel farther. See figure #5 in the article. I'm not trying to stick my thumb in your eye... so don't take offense. I just think we are saying a similar thing using different terms. It is not the sails thickness that increases the leeward path length, it is the shape of the sail and its aspect to the wind that creates a longer path. If the air has to travel farther, then the individual air molecules are farther apart on the leeward side... = less pressure.
In reading the site it states..
"The circulation flow field causes a
large amount of air to flow on the top (lee side) of the airfoil.
The same amount of air is flowing between each pair of
streamlines. The speed of the flow increases in areas where the
streamlines get closer together such as near the leading edge of
the airfoil. Higher speeds mean lower pressures. Where the
streamlines get farther apart such as on the lower surface, the
flow slows down and the pressures get higher. Lower pressures
on top and higher pressures on the bottom mean that the airfoil
now has lift."
I believe that is what I said when I stated that the air has farther to flow on the leeward side. And in order to catch up with the windward side air it must travel farther. See figure #5 in the article. I'm not trying to stick my thumb in your eye... so don't take offense. I just think we are saying a similar thing using different terms. It is not the sails thickness that increases the leeward path length, it is the shape of the sail and its aspect to the wind that creates a longer path. If the air has to travel farther, then the individual air molecules are farther apart on the leeward side... = less pressure.
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