Mike: First of all thank you for buying my book and chart. If you any questions about any of the material just give me shout here or drop me an email at yankee3223@juno.com. In general this is how it works. The engine of a masthead rig is the jib and the engine of a fractional rig is the main. So on the masthead you want to focus your efforts first on the jib and on the fractional you want to focus first on the main. Next time you see a America Cup race check out where their main trim efforts are - it is with the mains.
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Trim the main first
Jeff: Yup, that's what I'm saying. If you have a fractional rig you trim the main first. The engine on a fractional rig is the main. Generally, fractionals have small jibs anyway so why waste time fooling with it. If your fractional has a 150 then I would deal with the jib first but the main is everything, so if a bubble develops in the main I'd sacrifice the jib and ease it out. On a masthead I would not mess with the jib and would move the main if I wanted to get rid of the bubble. On a masthead rig you trim the jib first unless you have a small 120 or 125. Then I would not mess much with it either. I'd go right to the main. You have to use your best judgement and let common sense be the dictator as it is impossable to deal with every variable in this small forum format. As I've mentioned before, knowing the WHY of what your doing is everything, otherwise a mate is just guessing.
Jeff: Yup, that's what I'm saying. If you have a fractional rig you trim the main first. The engine on a fractional rig is the main. Generally, fractionals have small jibs anyway so why waste time fooling with it. If your fractional has a 150 then I would deal with the jib first but the main is everything, so if a bubble develops in the main I'd sacrifice the jib and ease it out. On a masthead I would not mess with the jib and would move the main if I wanted to get rid of the bubble. On a masthead rig you trim the jib first unless you have a small 120 or 125. Then I would not mess much with it either. I'd go right to the main. You have to use your best judgement and let common sense be the dictator as it is impossable to deal with every variable in this small forum format. As I've mentioned before, knowing the WHY of what your doing is everything, otherwise a mate is just guessing.
If the Main is trimmed first........
....Wouldn't that, by definition, mean that the Jib will not be properly trimmed. The Jib is ALWAYS redirecting wind over the main, even if it is a fractional rig. Seems like trimming the main first will mean that we always have one sail that is improperly timmed (the jib). Seems that if the proper Angle of Attack is one of the goals of sail trimming, then what difference would it make if the main is trimmed to the apparent wind without the Jib, or the redirectd apparent wind from the jib. Either way, the main is "properly" trimmed. However, by trimming the jib first, now we have two properly trimmed sails instead of one. If we have proper twist controls, then we can compensate for different wind angles to the Main introduced by a fractional rig Jib. Jeff
....Wouldn't that, by definition, mean that the Jib will not be properly trimmed. The Jib is ALWAYS redirecting wind over the main, even if it is a fractional rig. Seems like trimming the main first will mean that we always have one sail that is improperly timmed (the jib). Seems that if the proper Angle of Attack is one of the goals of sail trimming, then what difference would it make if the main is trimmed to the apparent wind without the Jib, or the redirectd apparent wind from the jib. Either way, the main is "properly" trimmed. However, by trimming the jib first, now we have two properly trimmed sails instead of one. If we have proper twist controls, then we can compensate for different wind angles to the Main introduced by a fractional rig Jib. Jeff
Not really ..... Don is correct
Trimming the mainsail first will create the correct 'upwash' for the jib to operate in - making it more efficient as it can be adjusted for the correct stream flow. On a sloop: coarse adjust main, then coarse adjust jib, then finely adjust main, then jib ... for optimum output. The **trim of main and jib are interdependent on one another** - trimming the main will affect the air flow across the jib and vice versa. Doesnt matter if you have a masthead or fractional rig its just simple aerodynamics. Aerodynamics optimizing is somthing that can not be done by 'intuition'. --- thats why the use of telltales is sooooooooo important. The top sailors have known this since the mid 1970s, yet its amazing how old rules of thumb die so slowly ... just like false concepts of bernoulli effect and slot effect on sails are are still touted and bandied about to this day. The desciption that your high school science teacher gave you on what causes lift in a wing is ENTIRELY WRONG. Aero-science has know this for more than 3/4 of a century and yet these false hypothesis are still taught. Don is right !!!
Trimming the mainsail first will create the correct 'upwash' for the jib to operate in - making it more efficient as it can be adjusted for the correct stream flow. On a sloop: coarse adjust main, then coarse adjust jib, then finely adjust main, then jib ... for optimum output. The **trim of main and jib are interdependent on one another** - trimming the main will affect the air flow across the jib and vice versa. Doesnt matter if you have a masthead or fractional rig its just simple aerodynamics. Aerodynamics optimizing is somthing that can not be done by 'intuition'. --- thats why the use of telltales is sooooooooo important. The top sailors have known this since the mid 1970s, yet its amazing how old rules of thumb die so slowly ... just like false concepts of bernoulli effect and slot effect on sails are are still touted and bandied about to this day. The desciption that your high school science teacher gave you on what causes lift in a wing is ENTIRELY WRONG. Aero-science has know this for more than 3/4 of a century and yet these false hypothesis are still taught. Don is right !!!
I am always willing to learn....
What is wrong with the theory of what causes lift on a wing, and the slot effect ? If I can pick up a little speed, I'll relearn something. Thanks.....Jeff
What is wrong with the theory of what causes lift on a wing, and the slot effect ? If I can pick up a little speed, I'll relearn something. Thanks.....Jeff
Well .....
Bernoulli Theorem actually applies for flow inside of conduits/pipes, etc. The slot effect doesnt speed up air going through the 'slot' .... if that would happen the jib would be a very inefficient sail !!!!! Most of the 'theories' that are touted for lift, slot effect, etc. were merely 'speculation' and without any proof. Aerodynamicists have with the usage of instrumentation, etc. proved them to be quite WRONG. If you want a fairly good treatise of how sails get their 'lift' and how sails actuallly work go to www.arvelgentry.com and follow the 'magazine articles' sidebar. Caution - these articles are not for the technically-faint-of-heart and you may need to re-read them several times before they start to make sense. When reading such articles, leave your 'intuition' at home and read them with an open mind. As for increase of speed and efficiency (and after mastering Don Guilettes "Sail Trim Guide") you might want to venture into Gentry's tell tale (Gentry Tufts) system (also included in the 'magazine articles section') . Gentry was the reason the American entries of the Americas Cup matches did so well during the 70s & 80s, etc.
Bernoulli Theorem actually applies for flow inside of conduits/pipes, etc. The slot effect doesnt speed up air going through the 'slot' .... if that would happen the jib would be a very inefficient sail !!!!! Most of the 'theories' that are touted for lift, slot effect, etc. were merely 'speculation' and without any proof. Aerodynamicists have with the usage of instrumentation, etc. proved them to be quite WRONG. If you want a fairly good treatise of how sails get their 'lift' and how sails actuallly work go to www.arvelgentry.com and follow the 'magazine articles' sidebar. Caution - these articles are not for the technically-faint-of-heart and you may need to re-read them several times before they start to make sense. When reading such articles, leave your 'intuition' at home and read them with an open mind. As for increase of speed and efficiency (and after mastering Don Guilettes "Sail Trim Guide") you might want to venture into Gentry's tell tale (Gentry Tufts) system (also included in the 'magazine articles section') . Gentry was the reason the American entries of the Americas Cup matches did so well during the 70s & 80s, etc.
Rich, great back and forth here.....
... but I think I am still confused. What IS the theory of lift on a wing that is incorrect ? Also, I don't know about the slot effect speeding up airflow, but I do know that the airflow is redirected by the jib. Why would that not affect mainsail trim ? JB
... but I think I am still confused. What IS the theory of lift on a wing that is incorrect ? Also, I don't know about the slot effect speeding up airflow, but I do know that the airflow is redirected by the jib. Why would that not affect mainsail trim ? JB
Actually the airflow is redirected by bothsails .... and the net effect is that the stream flows 'circulate' about each sail. As I related before you cant use intuition when thinking about aerodynamics. What the mainsail does is causes the stream flow well in front of the boat to bend slightly thus giving the jib/genoa a 'lift' or better attack angle to operate in; plus, the 'slot' causes more air stream flow to occur/ move towards the lee side of the genoa, etc. Actually what is happening is a 'circulating' air flow around each sail .... and sometimes you can see the circulation flow net effect when the flows are unbalanced .... and you are watching the tell-tales. Very complicated to explain but you can get a better idea of whats happening from the aerodynamicist/sailor who discovered these actions on sails at: www.arvelgentry.com/magaz/How_a_Sail_Gives_Lift.pdf www.arvelgentry.com/magaz/Another_Look_at_Slot_Effect.pdf These were the 'seminal' articles that set the sailing world on fire and discounted/refuted all the old established and wrong theories.
Simpler explanations are available
One of the most comprehensive books I found on the subject is the Sail Trim manual published by North sails. You should be able to find it at your local WM store or on-line somewhere. I also found a website for WB Sails (a sailmaker in Finland) with a series of articles on trim. It also has some slick animations, wind tunnel photos and trim simulators. Click on the link below, then click on "News". North and WB both state that the two sails, when properly trimmed, should work together like a single airfoil, with the headsail acting as the front third (or thereabouts) and the mainsail functioning like the remainder. This is true regardless of whether the rig is fractional or masthead. Each type of rig has its own method for achieving this result. Now here's the high school physics refresher... A sail develops lift simply by changing the direction of the air flowing over it. Newton's first law of motion states that an object at rest or moving with constant velocity will continue to do so unless acted upon by an external force. Changing direction without changing speed is still a change in velocity and so requires a force. This force comes from the sail,,,you adjust it with the sheet. A luffing sail (no sheet tension) doesn't change the direction of the airflow and so develops no lift. Newton's third law of motion states that for every action (force) there is an equal and opposite reaction. The force needed to redirect the airflow around the sail must have an opposite reaction that acts on the sail. It is this reaction that we call "lift". When sailing upwind, the lift generated by the sailplan is oriented somewhere between dead ahead and dead abeam. Lift is a force and like all vectors it has magnitude and direction, It can be resolved into (represented by) two perpendicular components; one aligned dead ahead (the "driving force") and one oriented dead abeam (the "heeling force"). All else being equal, the ratio of driving force to heeling force improves as the boat bears away, and is optimal near a beam reach, which is why this is usually the fastest point of sail. Sorry for the physics lesson, but that's where the explanation is. Peter H23 "Raven"
One of the most comprehensive books I found on the subject is the Sail Trim manual published by North sails. You should be able to find it at your local WM store or on-line somewhere. I also found a website for WB Sails (a sailmaker in Finland) with a series of articles on trim. It also has some slick animations, wind tunnel photos and trim simulators. Click on the link below, then click on "News". North and WB both state that the two sails, when properly trimmed, should work together like a single airfoil, with the headsail acting as the front third (or thereabouts) and the mainsail functioning like the remainder. This is true regardless of whether the rig is fractional or masthead. Each type of rig has its own method for achieving this result. Now here's the high school physics refresher... A sail develops lift simply by changing the direction of the air flowing over it. Newton's first law of motion states that an object at rest or moving with constant velocity will continue to do so unless acted upon by an external force. Changing direction without changing speed is still a change in velocity and so requires a force. This force comes from the sail,,,you adjust it with the sheet. A luffing sail (no sheet tension) doesn't change the direction of the airflow and so develops no lift. Newton's third law of motion states that for every action (force) there is an equal and opposite reaction. The force needed to redirect the airflow around the sail must have an opposite reaction that acts on the sail. It is this reaction that we call "lift". When sailing upwind, the lift generated by the sailplan is oriented somewhere between dead ahead and dead abeam. Lift is a force and like all vectors it has magnitude and direction, It can be resolved into (represented by) two perpendicular components; one aligned dead ahead (the "driving force") and one oriented dead abeam (the "heeling force"). All else being equal, the ratio of driving force to heeling force improves as the boat bears away, and is optimal near a beam reach, which is why this is usually the fastest point of sail. Sorry for the physics lesson, but that's where the explanation is. Peter H23 "Raven"
Lift by the Bernoulli effect (for Jeff B)
Bernoulli's Principle states that as the speed of a moving fluid increases, the pressure within the fluid decreases. It was based on measured observations in the laboratory and is felt to be consistent with the principle of conservation of energy. I provided a link below to a website that explains the Bernoulli effect and lift in varying levels of detail and complexity. There are animations to help illustrate the principle. The classic explanation of how sails develop lift is based on the idea that air flowing around the leeward side (back) of a sail is moving faster than the air on the windward side. The pressure on the leeward side must therefore be lower and it is this difference in pressure between the two sides of the sail that generates "lift". Research (including extensive wind tunnel studies) has shown that this explanation has serious flaws. Common sense also disproves it. If the "pressure difference" were real it would easily be equalized by air flowing under the foot of the sail. If THAT were true, every headsail ever sold would be useless. Peter H23 "Raven"
Bernoulli's Principle states that as the speed of a moving fluid increases, the pressure within the fluid decreases. It was based on measured observations in the laboratory and is felt to be consistent with the principle of conservation of energy. I provided a link below to a website that explains the Bernoulli effect and lift in varying levels of detail and complexity. There are animations to help illustrate the principle. The classic explanation of how sails develop lift is based on the idea that air flowing around the leeward side (back) of a sail is moving faster than the air on the windward side. The pressure on the leeward side must therefore be lower and it is this difference in pressure between the two sides of the sail that generates "lift". Research (including extensive wind tunnel studies) has shown that this explanation has serious flaws. Common sense also disproves it. If the "pressure difference" were real it would easily be equalized by air flowing under the foot of the sail. If THAT were true, every headsail ever sold would be useless. Peter H23 "Raven"
OK, so what have we learned ?
That the jib redirects airflow, but dosen't speed up that flow (the traditional slot effect) That both sails redirect airflow. Which we already knew because a mizzin will be sheeted in far more than the head sail. That traditional explainations of "lift" may be incorrect. But, who cares. The sails still work. If we trim a mainsail without a jib, it will be trimmed to exactly the same position with a jib (Don's initial allegation - trim the Main first) I disagreed with the "Main trimmed first" theory. To carry to a furthur conclusion.... if we had three masts with the largest sail at the rear, would we still trim that sail first ? What if there were 4 masts and the largest sail was in the number 3 position. Would that one be trimmed first? If wind is redirected by the jib, without knowing or caring about whether it speeds up or not, or if upwash is present (because it is still redirected), then how can the main be properly trimmed without knowing the resultant (changed, or redirected)wind direction when the jib is brought in to play. My head hurts.....
That the jib redirects airflow, but dosen't speed up that flow (the traditional slot effect) That both sails redirect airflow. Which we already knew because a mizzin will be sheeted in far more than the head sail. That traditional explainations of "lift" may be incorrect. But, who cares. The sails still work. If we trim a mainsail without a jib, it will be trimmed to exactly the same position with a jib (Don's initial allegation - trim the Main first) I disagreed with the "Main trimmed first" theory. To carry to a furthur conclusion.... if we had three masts with the largest sail at the rear, would we still trim that sail first ? What if there were 4 masts and the largest sail was in the number 3 position. Would that one be trimmed first? If wind is redirected by the jib, without knowing or caring about whether it speeds up or not, or if upwash is present (because it is still redirected), then how can the main be properly trimmed without knowing the resultant (changed, or redirected)wind direction when the jib is brought in to play. My head hurts.....
Tell-tales !!!!!!!
" then how can the main be properly trimmed without knowing the resultant (changed, or redirected)wind direction when the jib is brought in to play." The answer is elegant, simple, aerodynamically correct: The tell-tales are flying correctly !!!!!!!! Next time that you're out sailing and the tell tales are behaving perfectly, hold course and then change the trim/shape on the mainsail .... and simply watch what happens to the tell tales on the jib !!!!!!! The tell tales dont know how to do aerodynamic calculations but simply react to the airstream flow. Ask yourself why the windward tales point ***forward*** when the boat is pinching, etc. - they are reacting to the component of circulation flow. ;-)
" then how can the main be properly trimmed without knowing the resultant (changed, or redirected)wind direction when the jib is brought in to play." The answer is elegant, simple, aerodynamically correct: The tell-tales are flying correctly !!!!!!!! Next time that you're out sailing and the tell tales are behaving perfectly, hold course and then change the trim/shape on the mainsail .... and simply watch what happens to the tell tales on the jib !!!!!!! The tell tales dont know how to do aerodynamic calculations but simply react to the airstream flow. Ask yourself why the windward tales point ***forward*** when the boat is pinching, etc. - they are reacting to the component of circulation flow. ;-)
Thanks, Peter
for suggesting something as basic as reading a book. Actually, there are some very good websites that also have moving pictures of sail flow, but I don't have the URLs for those anymore. Everyone's got a somewhat different opinion, and Bernoulli's no longer around to ask. Drats! Stu
for suggesting something as basic as reading a book. Actually, there are some very good websites that also have moving pictures of sail flow, but I don't have the URLs for those anymore. Everyone's got a somewhat different opinion, and Bernoulli's no longer around to ask. Drats! Stu
I have a question. Why not have tell-tails
on the forward part of a mainsail? Obviously back far enough from the mast so you don't get the dirty air from that. But why do we only hear about tell-tails on the leech of the mainsail? I know they are important there, but I bet many of us woulod learn alot about triming the Main if we had tell-tails about a 1/3 of the way back from the mast. Heck its easy to trim the jib, just get all the tell tails streaming correctly. I find getting the main to be perfectly in sync the difficult one.
on the forward part of a mainsail? Obviously back far enough from the mast so you don't get the dirty air from that. But why do we only hear about tell-tails on the leech of the mainsail? I know they are important there, but I bet many of us woulod learn alot about triming the Main if we had tell-tails about a 1/3 of the way back from the mast. Heck its easy to trim the jib, just get all the tell tails streaming correctly. I find getting the main to be perfectly in sync the difficult one.
One guy's answer
The airflow over the forward part of the foresail is more important than that over its leech, and the flow over the back part of the main is more important than that on its luff. On many boats the "happy bubble" of a backwinded (or whatever you want to call it) main is indicative of optimal trim with the set-up that boat has (for example, genoa track might not extend far enough aft for that size foresail.) You can put tell-tales wherever you want, and many people do (check "The Best of SAIL Trim" for some examples.) But beware of 'tell-tale fixation' - it can eat up concentration that might better be focused elsewhere.
The airflow over the forward part of the foresail is more important than that over its leech, and the flow over the back part of the main is more important than that on its luff. On many boats the "happy bubble" of a backwinded (or whatever you want to call it) main is indicative of optimal trim with the set-up that boat has (for example, genoa track might not extend far enough aft for that size foresail.) You can put tell-tales wherever you want, and many people do (check "The Best of SAIL Trim" for some examples.) But beware of 'tell-tale fixation' - it can eat up concentration that might better be focused elsewhere.
Why Study?
The more you study, the more you know, the more you know the more you forget, the more you forget, the less you know, the less you know, the less you forget, the less you forget, the more you know. Why study? With a fully battened main, I added tell-tales to the luff in the same postions as on the jib on the advice of a North Seminar instructor. They help, especially since it is hard to tell when the main would luff. His advice was that most people over trim---ease, ease, ease, prior to the point of luffing for best speed on both sails. Since I usually raise the main first, it usually gets trimmed first. But realistically, don't we usually tinker constantly with trim anyway, constantly aware of the interplay between sails? I do, until it drives the Admiral crazy, and she makes me stop, which I do until she engages in her predictable afternoon nap. Then I just have to make make sure she doesn't doze off while sitting on a traveler car control line or vang line.....
The more you study, the more you know, the more you know the more you forget, the more you forget, the less you know, the less you know, the less you forget, the less you forget, the more you know. Why study? With a fully battened main, I added tell-tales to the luff in the same postions as on the jib on the advice of a North Seminar instructor. They help, especially since it is hard to tell when the main would luff. His advice was that most people over trim---ease, ease, ease, prior to the point of luffing for best speed on both sails. Since I usually raise the main first, it usually gets trimmed first. But realistically, don't we usually tinker constantly with trim anyway, constantly aware of the interplay between sails? I do, until it drives the Admiral crazy, and she makes me stop, which I do until she engages in her predictable afternoon nap. Then I just have to make make sure she doesn't doze off while sitting on a traveler car control line or vang line.....
Tinkering with the sails
Dean: Your wife must be my wifes sister so do what I do - run all your mainsail and jib control lines back to the helm!! I even had Garhauer build me a 3' winch handle. With the winch handled and the adjustable fairlead system I've got the jib covered. On telltales - I've been on a lot of boats where the skipper tells me he does not need them. I know what I'm looking for from a sail trim standpoint and I've only met one guy who was the best at sail trim w/o telltales that I've ever seen. Even though I know what I'm looking for I can only get so far without telltales. I need them for that extra ounce I'm trying to get out of the sails. It is kind of funny you mentioned telltales because before I read your message I was sitting here thinking about a new topic and I thought about telltales so I'm glad you brought it up. The topic is going to be "who does not want to go fast?".
Dean: Your wife must be my wifes sister so do what I do - run all your mainsail and jib control lines back to the helm!! I even had Garhauer build me a 3' winch handle. With the winch handled and the adjustable fairlead system I've got the jib covered. On telltales - I've been on a lot of boats where the skipper tells me he does not need them. I know what I'm looking for from a sail trim standpoint and I've only met one guy who was the best at sail trim w/o telltales that I've ever seen. Even though I know what I'm looking for I can only get so far without telltales. I need them for that extra ounce I'm trying to get out of the sails. It is kind of funny you mentioned telltales because before I read your message I was sitting here thinking about a new topic and I thought about telltales so I'm glad you brought it up. The topic is going to be "who does not want to go fast?".
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