I'm still trying to get used to my 86 C27. Had her out yesterday in 15+ mph. With a 150 up, she drove very nicely, w/o undue weather helm, but I couldn't get the main to set right. In an area encompasiing about the middle third of the luff and back several feet toward the leach, I had what appeared to be a bubbled out area. I tried everything I know to move the draft forward, thinking that it was a leeward side detachment bubble. I flattened out the sail as much as I could. At one point, I even had the boom positioned dead amidship with the traveller, and the sheet eased to put some of the sail back into something approaching a normal angle of attack. Nothing really worked. Wind piped up some more, so I droped the 150 and set a 110. Viola! Main sets perfectly (or as perfectly as a slightly blown out sail is going to set). So ... is the 150 backwinding the main, and how do I deal with that? Tom Monroe Carlyle Lake
backwinded main?
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Backwinded Main
Tom: The bubble in the main is probably coming from the jib and it is a common occurance when the jib is in too tight and the slot between the two sails becomes clogged. Ease the jib sheet a bit and it will probably go away.
Tom: The bubble in the main is probably coming from the jib and it is a common occurance when the jib is in too tight and the slot between the two sails becomes clogged. Ease the jib sheet a bit and it will probably go away.
Tom M. That happens to a lot of masthead boats
with Larger genny's. Especially when hard on the wind. I understand what Don is suggesting but I wouldn't ease the jib sheet if it now caused the jib to be improperly trimmed and the tell tales are not streaming well. I was on a custom Tripp 37 doing the around Block Island Race and asked the skipper about that. He says don't worry about it too much, and especially don't try and adjust things and overly flatten out the main or let out the genny too much to get rid of it. Just trim your sail as you normally would. The biggest power on your boat is in the Genny, so get the Genny trim perfectly and tell tales streaming well and then adjust the main sail so all the tell tails on the leech of the main sail are just streaming and the top one just fluttering. I think you will find your speed best there even with the bubble. I have read that the mainsail on our boats can be looked at as more of an "afterburner" and the slot can actually increase the speed of the wind going over the Genny. I have also heard its the wind speed at the aft end of your mainsail that matters the most for the best speed and I think the bubble usually shows up in the front of the mainsail. (Obviously you don't want to "choke" the slot and you have to really play with them to get them working together). I don't have the complete answer-it really depends. But if the bubble is really big I'm sure it can effect your speed. From a North Sails site it says "If you have a lot of backwind, chances are your (jib) lead is too far forward. Slide the lead back and monitor the backwind. It may never go away, but it should help ...." Another sail maker says "At this time the front of the main will have a large bubble in it, caused by the large volume of air exiting off the leech of the genoa. This is known as backwinding the mainsail. It may look awkward, but it is the fastest arrangement given the constraints. If we look at this same circumstance using a full batten main, the battens will prevent the bubble from forming in the luff, essentially forcing the mainsail down into the high speed exhaust flowing off the jib. This is now constricting the air flow, essentially acting like an air dam, preventing the air from exhausting off the leech of the jib. This will be a performance liability...but it will "look better." http://www.pineapplesails.com/articles/fullbatt.htm Here are some other discussions on this. http://www.setsail.com/c_central/sail_advice/sail_advice.html#optimum
with Larger genny's. Especially when hard on the wind. I understand what Don is suggesting but I wouldn't ease the jib sheet if it now caused the jib to be improperly trimmed and the tell tales are not streaming well. I was on a custom Tripp 37 doing the around Block Island Race and asked the skipper about that. He says don't worry about it too much, and especially don't try and adjust things and overly flatten out the main or let out the genny too much to get rid of it. Just trim your sail as you normally would. The biggest power on your boat is in the Genny, so get the Genny trim perfectly and tell tales streaming well and then adjust the main sail so all the tell tails on the leech of the main sail are just streaming and the top one just fluttering. I think you will find your speed best there even with the bubble. I have read that the mainsail on our boats can be looked at as more of an "afterburner" and the slot can actually increase the speed of the wind going over the Genny. I have also heard its the wind speed at the aft end of your mainsail that matters the most for the best speed and I think the bubble usually shows up in the front of the mainsail. (Obviously you don't want to "choke" the slot and you have to really play with them to get them working together). I don't have the complete answer-it really depends. But if the bubble is really big I'm sure it can effect your speed. From a North Sails site it says "If you have a lot of backwind, chances are your (jib) lead is too far forward. Slide the lead back and monitor the backwind. It may never go away, but it should help ...." Another sail maker says "At this time the front of the main will have a large bubble in it, caused by the large volume of air exiting off the leech of the genoa. This is known as backwinding the mainsail. It may look awkward, but it is the fastest arrangement given the constraints. If we look at this same circumstance using a full batten main, the battens will prevent the bubble from forming in the luff, essentially forcing the mainsail down into the high speed exhaust flowing off the jib. This is now constricting the air flow, essentially acting like an air dam, preventing the air from exhausting off the leech of the jib. This will be a performance liability...but it will "look better." http://www.pineapplesails.com/articles/fullbatt.htm Here are some other discussions on this. http://www.setsail.com/c_central/sail_advice/sail_advice.html#optimum
Backwinded Main
Tom S: I'm trying to keep my answer as simple as possable. Tom Monroe sounds to me like a cruiser, who is just trying to get a simple bubble out of his main. He is not racing around the world. I would bet that if he actually looked closely at his jib and read his telltales he would find that he has the jib in too tight. Too tight is a relative term but that is what the bubble in the main is telling him. It is one of two things, either the main is incorrect or the jib is. All he has to do is experiment and ease the jib out slightly and see what happens. If he loses a lot of speed, which he won't, then he just cranks it back in, gets his telltales flowing, and lives with it or he cranks in the mainsail a bit. Either movement will get rid of the bubble. Regardless of what other may say - and everyone has an opinion on this stuff - common sense says that the wind likes to be "attached" to both sails and the bubble is a problem for wind flow. How many airplane wings have bubbles in them and your sails are like airplane wings. My advise to anyone reading this stuff is digest all the information and then go out and try the various ideas on your boat and see what works for you. That's what I had to do when I started researching sail trim. My main concern is to not make it more complicated than it actually is and if the advise doesn't work when you test it out, then disregard it and try something else. I forget what I was looking at but a while back I was reading an article by some author and ironically , the next day I found one on the same subject by Buddy Melges. Both articles were directly opposite but both seemed plausable. l didn't know who to believe so I tried both ideas out on my C30 - Buddy was right!! I'm no Buddy Melges but just try out what I say and see if it works for you.
Tom S: I'm trying to keep my answer as simple as possable. Tom Monroe sounds to me like a cruiser, who is just trying to get a simple bubble out of his main. He is not racing around the world. I would bet that if he actually looked closely at his jib and read his telltales he would find that he has the jib in too tight. Too tight is a relative term but that is what the bubble in the main is telling him. It is one of two things, either the main is incorrect or the jib is. All he has to do is experiment and ease the jib out slightly and see what happens. If he loses a lot of speed, which he won't, then he just cranks it back in, gets his telltales flowing, and lives with it or he cranks in the mainsail a bit. Either movement will get rid of the bubble. Regardless of what other may say - and everyone has an opinion on this stuff - common sense says that the wind likes to be "attached" to both sails and the bubble is a problem for wind flow. How many airplane wings have bubbles in them and your sails are like airplane wings. My advise to anyone reading this stuff is digest all the information and then go out and try the various ideas on your boat and see what works for you. That's what I had to do when I started researching sail trim. My main concern is to not make it more complicated than it actually is and if the advise doesn't work when you test it out, then disregard it and try something else. I forget what I was looking at but a while back I was reading an article by some author and ironically , the next day I found one on the same subject by Buddy Melges. Both articles were directly opposite but both seemed plausable. l didn't know who to believe so I tried both ideas out on my C30 - Buddy was right!! I'm no Buddy Melges but just try out what I say and see if it works for you.
Backwinded but fast
I race on Green Bay and and Inland lakes. Most of the racers I see have a backwind bubble about 1/3 to 1/2 of the luff when sailing close to the wind. It's fast. The only time I don't allow a bubble is in very light wind conditions but then the sail is fairly flat to maintain laminar flow and we're not pointing as high. My trim is as follows: Trim the foresail for the heading. Get all telltails, inner and outter, flowing. Luff tension should allow speed wrinkles. Trim main till the top tell tail stalls about half the time. Luff should have speed wrinkles. Go Fast! Some guys sail with the inner foresail tells stalling a bit but they usually have other excuses for finishing so far behind. Another thing: Lots of folks think that a flat luff in the foresail is fast. I don't think so. The curve changes the effective trust of the sail more forward.
I race on Green Bay and and Inland lakes. Most of the racers I see have a backwind bubble about 1/3 to 1/2 of the luff when sailing close to the wind. It's fast. The only time I don't allow a bubble is in very light wind conditions but then the sail is fairly flat to maintain laminar flow and we're not pointing as high. My trim is as follows: Trim the foresail for the heading. Get all telltails, inner and outter, flowing. Luff tension should allow speed wrinkles. Trim main till the top tell tail stalls about half the time. Luff should have speed wrinkles. Go Fast! Some guys sail with the inner foresail tells stalling a bit but they usually have other excuses for finishing so far behind. Another thing: Lots of folks think that a flat luff in the foresail is fast. I don't think so. The curve changes the effective trust of the sail more forward.
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