I have roller furling and I want to take power off the jib upwind in medium waves and wind with some gusts. Good and bad, what will twisting get me compare to shortening and maintaining the same twist?
Twist or shorten?
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Quoddy: Good question but you may be surprised that there is a little more to think about as you’ll see with my answer. Before I continue I want to point out that what I’m suggesting in answering your question is really counter productive to what you’re trying to do and that is power through chop.
My answer depends on the type of fairlead system you have – pin type or adjustable. There are a number of different mainsail trim controls that adjust draft depth, draft position, twist and angle of attack. The problem with the jib, from an adjustment standpoint, is the fairleads are used to adjust all 4 of the above elements. If you have an adjustable fairlead system it doesn’t matter whether you flatten the sail or induce twist first.
Flattening the sail or inducing twist, before you start to roll up the sail, are your first two options. A flat sail is a less powerful sail. The way sail shape works is you start out with a relatively flat sail and then as the wind pipes up you gradually induce draft depth until you get up to about 12 knots of wind and then you start to gradually flatten the sail thus de-powering it.
So let’s assume you have a pin type fairlead system, which is pain to deal with when the sail is powered up. The first thing I’d do is flatten the sail which you can do with the jib sheets, jib halyard and mast bend (if you had a bendy mast). You really need the fairlead to be adjusted but it is a lot of work.
If flattening the jib does not get you the results you desire then the next thing you do is induce twist bit you need to use the fairlead for that that adjustment. In none of that works then start rolling up the sail but you have to reset all the controls when you get to the position you want. In all of this you can’t forget the mainsail.
As I mentioned, if I was trying to power through chop I would do none of the above.
My answer depends on the type of fairlead system you have – pin type or adjustable. There are a number of different mainsail trim controls that adjust draft depth, draft position, twist and angle of attack. The problem with the jib, from an adjustment standpoint, is the fairleads are used to adjust all 4 of the above elements. If you have an adjustable fairlead system it doesn’t matter whether you flatten the sail or induce twist first.
Flattening the sail or inducing twist, before you start to roll up the sail, are your first two options. A flat sail is a less powerful sail. The way sail shape works is you start out with a relatively flat sail and then as the wind pipes up you gradually induce draft depth until you get up to about 12 knots of wind and then you start to gradually flatten the sail thus de-powering it.
So let’s assume you have a pin type fairlead system, which is pain to deal with when the sail is powered up. The first thing I’d do is flatten the sail which you can do with the jib sheets, jib halyard and mast bend (if you had a bendy mast). You really need the fairlead to be adjusted but it is a lot of work.
If flattening the jib does not get you the results you desire then the next thing you do is induce twist bit you need to use the fairlead for that that adjustment. In none of that works then start rolling up the sail but you have to reset all the controls when you get to the position you want. In all of this you can’t forget the mainsail.
As I mentioned, if I was trying to power through chop I would do none of the above.
Twist First?
Don, if the problem is gusts, I thought that twist is better shedding power from gusts, while flattening the sail depowers it at all wind speeds. If I'm wrong, then why?
Thanks, as always!
Don, if the problem is gusts, I thought that twist is better shedding power from gusts, while flattening the sail depowers it at all wind speeds. If I'm wrong, then why?
Thanks, as always!
Twist or shorten
Don, I thought bending the mast will only flatten the main. How does bending the mast flatten the headsail? If you bend the mast by tensioning the backstay you will also tension the headstay which will flatten the headsail, but bending the mast alone will not flatten the headsail. You could also bend a mast by tensioning the babystay if the boat was fitted with one but this would not increase headstay tension or flatten the headsail.
Don, I thought bending the mast will only flatten the main. How does bending the mast flatten the headsail? If you bend the mast by tensioning the backstay you will also tension the headstay which will flatten the headsail, but bending the mast alone will not flatten the headsail. You could also bend a mast by tensioning the babystay if the boat was fitted with one but this would not increase headstay tension or flatten the headsail.
Twist or shorten
Quoddy, generally speaking, when you need to reduce sail area or put more twist in your sails, the conditions are usually high winds and choppy seas. When you twist your sails, the angle of attack will vary from the tack to head of your sail. This is exactly what you need to keep the sails driving while the boat is pitching and wandering off in different directions as you try to head upwind. You want some portion of the sail to be drawing correctly at all times. Twist will also reduce the healing forces by lowering the center of effort because the top of the sail can be twisted off so much that it is no longer part of the driving or heeling forces . Compare this to a sail that is trimmed with less twist ad less sail area. The angle of attack from tack to head will be fairly similar. As the boat is pitching and off course, the sails will only be correctly trimmed part of the time. This is slow for lack of drive.
Quoddy, generally speaking, when you need to reduce sail area or put more twist in your sails, the conditions are usually high winds and choppy seas. When you twist your sails, the angle of attack will vary from the tack to head of your sail. This is exactly what you need to keep the sails driving while the boat is pitching and wandering off in different directions as you try to head upwind. You want some portion of the sail to be drawing correctly at all times. Twist will also reduce the healing forces by lowering the center of effort because the top of the sail can be twisted off so much that it is no longer part of the driving or heeling forces . Compare this to a sail that is trimmed with less twist ad less sail area. The angle of attack from tack to head will be fairly similar. As the boat is pitching and off course, the sails will only be correctly trimmed part of the time. This is slow for lack of drive.
Re: Twist First?
David: I was doing the best I could with the two sentence question. I wouldn't proceed that way but I have to try to answer the question and added some stuff he didn't ask about. He was trying to "take power off the jib in medium waves and wind and some gusts". In those conditions twisting off the main and jib is the last thing I would do because I need all the power I can get to power through the chop and I wouldn't flatten the sails either, but if a mate wanted to de-power that is how he would do it..
Additionally, in wind gust whic are a temp situation, The easiest remedy is to drop the traveler, which reduces the angle of attack and does not change the shape of the sail. When the gust passes you merely return the traveler to its former position and sail away until the next gusts hits.
David: I was doing the best I could with the two sentence question. I wouldn't proceed that way but I have to try to answer the question and added some stuff he didn't ask about. He was trying to "take power off the jib in medium waves and wind and some gusts". In those conditions twisting off the main and jib is the last thing I would do because I need all the power I can get to power through the chop and I wouldn't flatten the sails either, but if a mate wanted to de-power that is how he would do it..
Additionally, in wind gust whic are a temp situation, The easiest remedy is to drop the traveler, which reduces the angle of attack and does not change the shape of the sail. When the gust passes you merely return the traveler to its former position and sail away until the next gusts hits.
Re: Twist or shorten
Ted: On bending the mast - I'm sorry I brought that topic up. I hate that topic. Later on that day when I re read the post I wished I had never added it but it was too late to get rid of it.
Ted: On bending the mast - I'm sorry I brought that topic up. I hate that topic. Later on that day when I re read the post I wished I had never added it but it was too late to get rid of it.
Then why not
add a qualifier? Like: "...for those masts that do bend (and many do not)..."
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