Talk:Sail

What
How is a sail a vertically oriented wing? A sail works by air pushing against it, a wing works by pressure differences from the wing cutting through the air.
 * That's the difference between some kinds of downwind sail-setting and all the rest: In extreme downwind sailing the sail, as an aerofoil, has indeed stalled and the wind is simply 'pushing against it' - in that case setting a spinnaker or 'tacking downwind' will improve performance and boat stability. In all other cases, from beating upwind to broad reaching, each sail works by exactly the same mechanism of pressure differences as a wing and an aerofoil. The luff is the leading edge and the leech is the trailing edge.  A well-set spinnaker or criuising chute works as an aerofoil too, but the aerofoil is vertically oriented with two leading edges beginning at the head and the foot being the trailing edge.  The same is true of square-rig sails, when off the wind.  When on the wind, a square-rigger's windward tacks are hardened down and the two side edges of the sail become leading and trailing edges respectively.  Can we work these ideas into the article somewhere? --Nigelj 10:38, 13 November 2005 (UTC)


 * I edited the Wing entry to include sails as a kind of wing, I'll try to do as you suggest NigelJ

TonyClarke 16:08, 13 November 2005 (UTC)

Sails as wings?
I think that this might be an oversimplification of the matter, as it depends largely on both the type of rigging being used and the direction (relevant to the wind direction) that one wishs to go.

For instance, many of the large square rigged ships did move essentially through the force of the wind pushing on the sail. I suppose technically the wind is piling up behind the sail (thus high pressure area) and the difference in pressure between the higher and lower pressure areas on opposite sides of the sail causes it to move, which is the same principle as that which generates lift. However, unlike in the case of aerofoils (aka wings) there is *not* a higher wind speed going across the back of the sail than the front.

In short, while the pressure differential as cause of movement remains valid, the cause of these pressure differences is not the same as for wings.

Lift (force)

Anyway, hope this helps.

I suppose another question would be for information sources explaining this. Anyone have any good sources of information to base this on? The one link provided on the page (Perfect sails or something to that effect) is a bit overtechnical, and I'm not sure about it.

Zitchas


 * Sorry, Zitchas, but this is wrong, wrong, wrong. Sails are aerofoils and, when they are not stalled, they do produce lift exactly like aircraft wings do, although often in directions other than 'up'.  When sails are stalled they produce a little lift and lots more drag, just like wings too (though the drag is often in directions other than 'backwards', and so can power a boat downwind).  Instability of the turbulent air behind a stalled sail often amplifies the rolling of a boat downwind, and is very inefficient on all other points of sail, so skippers avoid it if at all possible.  The tosh about lift resulting from higher wind speeds due to thick aerofoil shapes is fully debunked in Lift (force).  As I understand it, the benefit on aircraft of 'rounded' leading edges and 'thickness' in the aerofoils is to broaden the range of angles of attack that do not result in a stall.  This range of angles is minimal for a very thin aerofoil like a sail, although this is then mitigated slightly by the fact that the sail cloth is not rigid and so can adapt slightly (e.g. luffing).  Nonetheless, this narrow range of good angles for each sail is what keeps sail-trimmers busy when racing. --Nigelj 15:46, 10 December 2005 (UTC)

So then, wings are a  specialised type of sail ;-) Bcebul (talk) 00:51, 9 June 2011 (UTC)
 * Sails are soft (ie they can flap) and have no internal space (ie one sheet of material). Wings are hard (ie they cannot flap) and have some internal space between two surfaces of materials.  If a wing is installed on a boat to provide propulsion it is commonly referred to as a wing sail Boatman (talk) 08:01, 9 June 2011 (UTC)
 * Not that this is particularly relevant to the discussion, but the lower surface of a rigid wing is not a necessity, it just improves performance. A rigid wing consisting only of only one surface works: it can be flat or curved.  Some cheap balsa model gliders use such wings.--Gautier lebon (talk) 07:18, 10 June 2011 (UTC)
 * Birds may have something different to say about non flapping hard wings! Bcebul (talk) 21:58, 9 June 2011 (UTC)

OUTDENT. Folks, we seem to be getting into a well-intentioned editing war regarding how to explain how sails work. As most of us know, there are many different possible explanations, all correct. Some people like to model a sail as a rigid wing, others don't like that model. May I suggest that we work out a consensus text on the talk page? The consensus text should be addressed to the average reader, who presumably does not know much about physics, and should give references so that interested people can learn more. The consensus text should also mention that there are different models and different theories, each of which has its pros and cons (just as light can be usefully, and correctly, modelled as waves or particles, depending on what you are trying to explain/predict). --Gautier lebon (talk) 07:14, 10 June 2011 (UTC)

Alright then
Sounds like you know what you're talking about, so I guess I'll cede the point. What's a day if I don't learn something, after all? Thanks for the clarification.

Diagram
This article could use a simple diagram showing how a sail works. Qutezuce 08:08, 27 May 2006 (UTC)

Contradiction
I've just removed this from the article. If someone who knows about this could incorporate it back, it would be nice, but as it stands it reads like a comment and contradicts the preceeding paragraph.

''
 * The statement above is not correct.
 * As the boat moves downwind is is moving forward (relatively)and the apparent wind moves from
 * directly behind the boat to foward as indicated by streamers and indicators located at various points on the boat.
 * The sails are actually creating lift thus allowing the boat (in some cases)to move along faster than the wind.
 * The keel creates a righting moment, like gravity and the sails are resisting the forces of gravity on them,
 * that resistance is converted to a forward motion of the boat.

'' --Aioth 13:14, 30 October 2006 (UTC)

Sailing against the wind
I'd appreciate something on the history of sails, who invented them & when (I've seen Egyptians credited, c3000BC), what materials were used (canvas? silk? cotton?), when the rigid wingsail was invented & by who, so forth. Trekphiler 14:38, 21 November 2006 (UTC)

Sailing re-organization effort
Take a minute to read the comments at Talk:Sailing#Re-write effort -- non how-to et seq. Some of us a working on re-organizing the sailing-related articles. See if you agree with our approach and give us some help. Mrees1997 19:41, 29 December 2006 (UTC)

Scaling
I have the impression, that new boats have larger sails. In the past many small sails were used, now two big one suffice? Where is the limit? Arnero 21:02, 7 July 2007 (UTC)

My two cent
First of all, I'd like to ask, where the bugger is the square rig? Square riggings where used in a large part of the history of sailing in Europe and also in the medderterainan till the bysantins where beaten by the Arabs that where using Latin sails... And as the sqear riggings are main competitors to the fore and aft rigs it should atleast be mentioned in a article about sailing.

As for the scaling part of everything... The square rigs have one major disadvantage compared to fore and aft rigging, and that is that you require a larger and more experienced crew on a ship with that rig to be able to perform comparable with a ship with a fore and aft rigging. The larger the sails where the harder they where to handle so at least in the beginnings it was usual to have small sails as each sail then becomes manageable with a smaller crew. This also was a advantage in naval battles as losing one sail was afecting the overall performance of the ship less, you hopefully had other sails remaining. Later one people invented new ways to manage the sails new ways using ropes and stuff.. And later then that the fore and after rigs being more managable by a small crew also al owed a larger sail. Well that's what I can think of any ways.. might not be what you where looking after thou... Luredreier 19:09, 5 October 2007 (UTC)

Windmill sails
A sail is any type of surface intended to generate thrust by being placed in a wind—in essence a vertically-oriented wing.

Isn't that exactly what a windmill sail does? The sail is so designed that the thrust produced is converted to rotary motion. Does this need adding to this article or as a new article? —Preceding unsigned comment added by Mjroots (talk • contribs) 09:51, 21 January 2008 (UTC)

And..... A wing generates lift. A sail is pushed on directly. This is like saying a plane sails straight up with vertical winds... —Preceding unsigned comment added by 141.109.108.119 (talk) 11:45, 23 November 2008 (UTC)

Sails with motors?
Something to clarify: No sail has any bits of engine or motor? --Menchi 02:32 8 Jun 2003 (UTC)


 * Flettner rotors (I may not have that spelled right) do have motors, but they are rarely used on purely sailing vessels. The are found (when found at all) on hybrid motor/sailing vessels that use the windpower to increase efficiency.  The rotors work much like a golf ball; they are cylinders with a dimpled surface that is rotated at high speed.  As the wind passes across the moving surface, the side going with the wind pulls the air further than the side going against the wind, which generates lift at 90 degrees to the wind.  Reverse the direction of rotation, and you reverse the direction of lift.  I don't know that any energy is lost (other than normal frictional losses) when generating the lift; if there is no additional energy loss, then the motor is not putting any energy into the generation of lift, and you coud consider the rotors to be "pure" sails.  scot 14:09, 22 Apr 2005 (UTC)

Pressure?
Just a second, what does air pressure have to do with simple pushing? I'm not creating a difference in pressure on something when i kick it, am i?


 * Pressure being force over area, yes you are, if only for a short time. PeteVerdon 10:14, 1 November 2005 (UTC)

Triangular sails
In the history section, it is claimed that ships with triangular sails didn't appear until the 17th century, however this other article claims otherwise: Lateen

Arabs invented sails??
How can "The Arabs [have] invented the sail in about 2,000 BCE" be true when "The first written attestation of the ethnonym "Arab" occurs in an Assyrian inscription of 853 BCE" (from wiki page on Arabs). I believe that the Arabs invented lateen (triangular) sails but did it much later - square sails had been around for a while. —Preceding unsigned comment added by Laetoli (talk • contribs) 23:03, 14 June 2010 (UTC)

Comments
Hi, everyone. I'm James T Phelan and I know nothing about sailing and I came to this page by accident. I totally support the concept of Wikipedia and hope to contribute where I can but it seems to me that this article highlights two main problems: inconsistent information and bad grammar. Ignoring for the moment the unnecessary use of "had", the article says "The Arabs had invented the sail in about 2,000 BCE in an attempt to establish trading routes around the Persian Gulf. The Chinese had designed sails around 3,000 BCE, and can still be seen on traditional wooden ships sailing off the coast of Vietnam in Ha Long Bay."

What this says is that (1)the Arabs invented sails but the Chinese designed them 1000 years before the Arabs invented them; (2)Chinese people can still be seen on traditional wooden ships.

And how come a company - Glowfast - is allowed to have blatant advertising in the article? James T Phelan (talk) 01:10, 27 June 2010 (UTC)


 * Hi James. Thanks for you comments. I have tried to improve some of the clunky grammar in the History section. I have also changed the commercial puff into a more useful reference. While I was there, I added something about tell-tales, as these are related and probably more common.


 * Per your comments, and those in the 2 sections just above, I am not sure about the facts as presented in the History section either. As I said in my edit commentary, some references there would be good, per WP:V. Some of that section is almost certainly either WP:UNDUE weight, or at least a bit muddled. I am no expert, but I will look out for some reference works that may clarify the key points of the development and history of sails and sailing worldwide.


 * Lastly, it's true that a top-level article like this attracts a lot of cruft and sometimes well-meaning but confused additions by random individuals. It is a job to keep up with all this and it's always helpful to be given a heads-up when things are below their best. So, thanks again. --Nigelj (talk) 10:43, 27 June 2010 (UTC)

Not just a wing
OK, I understand very little about sails, but I see something wrong with the opening statement: "A sail is any type of surface intended to generate thrust by being placed in a wind—in essence a vertically-oriented wing." As I understand it, sails usually function that way, but not always. What about spinnakers? Square rigged ships sailing before the wind? Isaac Rabinovitch (talk) 06:38, 15 September 2010 (UTC)
 * There is ususally a bit of spill (laminar flow) even in those circumstances, so the opening statement is correct: note the qualification in essence. No laminar flow at all (completely stalled surface) is an exception.--Gautier lebon (talk) 07:21, 15 September 2010 (UTC)
 * Agreed. Both spinnakers and square sails off the wind are usually rigged to encourage top-to-bottom flow. This not only stabilises the forces and helps prevent rolling, but provides some actual (vertical) lift, to help keep the vessel's bow out of the water and reduce drag. Should we make this more clear in the article? --Nigelj (talk) 09:00, 15 September 2010 (UTC)
 * I think it is already there, in the section on sail aerodynamics. But clarification and repetion are always helpful, so I would support adding something. I didn't do it myself because I couldn't see where to add anything, but maybe somebody else can.--Gautier lebon (talk) 14:14, 15 September 2010 (UTC)
 * While it's true that square rigged sails act a bit like wings, this is a secondary effect. The primary phenomenon when going down wind is that the sail stops the air rather than deflecting it to produce lift so I'd disagree with the phrase "in essence". In essence, it's a barn door. Mr swordfish (talk) 14:07, 15 September 2010 (UTC)
 * No, in essence a modern sail is a wing. It acts like a barn door only in exceptional circumstances.  That is also true of square rigs.  They were rarely used in the pure "barn door" configuration, which is very inefficient.  There was usually some laminar flow, as Nigel says above.--Gautier lebon (talk) 14:14, 15 September 2010 (UTC)
 * Is a wing still a wing when it's stalled?  I think so.  But does it "act" as a wing when it's stalled?  Sails are intended to be used in stalled-mode some of the time, and I'm not sure how useful it is to think of them as "wings" in this scenario.  The article talks about the two distinct ways sails work - perhaps the "vertically oriented wing" should be applied only to the second. Mr swordfish (talk) 14:07, 15 September 2010 (UTC)
 * Yes, a wind is a wing even when it is stalled. It just isn't very efficient at generating lift when it is stalled.  Sails are NOT intended to be used in stall-mode some of the time, they just wind up in that mode because there is no choice.  Whenever you have a choice, you use it in the laminar flow mode.  The laminar flow mode is the preferred mode, so "in essence" appears correct to me.--Gautier lebon (talk) 14:14, 15 September 2010 (UTC)
 * > Sails are NOT intended to be used in stall-mode some of the time
 * Really? I don't recall seeing a label on my sails that said "WARNING this sail is not intended for going dead down wind."  Of course sails are intended to be used in stall mode - it may not be the primary design criteria, but the fact is that boats go downwind and sail makers are well aware of this fact.


 * I'm skeptical that it's a useful metaphor to think of a typical sloop rig as acting like a "wing" when it's going dead downwind. Mr swordfish (talk) 14:04, 16 September 2010 (UTC)


 * But the point is that hardly anybody goes dead downwind with a typical sloop rig, because it is almost always faster to tack (gybe) downwind. Even with a spinnaker.  And if you are using a spinnaker there is some laminar flow even if you decided to go dead downwind, as stated above.  So most of the time the sail does act as a non-stalled wing.  And sails (especially modern sails) are indeed not designed to be used when stalled, otherwise they wouldn't have built-in curvature.  A sail designed (intended) to be used in stall mode would be perfectly flat.  I haven't seen many of those on contemporary boats.  Anyway, this discussion might be more productive if you were to propose an actual edit to the text of the article.  We could then discuss the merits of the proposed edit.--Gautier lebon (talk) 15:23, 16 September 2010 (UTC)


 * > hardly anybody goes dead downwind with a typical sloop rig, because it is almost always faster to tack (gybe) downwind


 * This depends on the boat. Modern sportboats make better VMG dead downwind by sailing hotter angles, but many traditional sloops do not.  Anyway,  regardless of the popularity or utility of dead downwind sailing, it exists and when it occurs the sail acts in a way that is fundamentally different than when the sail is not stalled.  For this mode of sailing, the wing metaphor is not terribly useful.


 * Actually, I question the usefulness of the wing metaphor at all, since it assumes that the reader understands how wings work, and that's hardly a given - most people don't have a clue how wings work.  All that said, I don't feel strongly enough about it to remove the "vertical wing" explanation from the article, but I do think Isaac Rabinovitch has a point.  —Preceding unsigned comment added by Mr swordfish (talk • contribs) 19:36, 16 September 2010 (UTC)
 * I would dispute your statement that traditional sloops cannot make better downwind VMG by gybing downwind, but I don't have references at my fingertips. The purpose of the wing analogy, as I see it, is precisly to alert readers to the fact that the way a sail functions may be quite different from what they thought, and to motivate them to find out how a wing works.  But I guess this discussion is closed, since there are no proposals for actual changes to the text of the article.--Gautier lebon (talk) 09:48, 17 September 2010 (UTC)::
 * The purpose of all statements in an article is to inform. If a statement isn't objectively true, it shouldn't be in the article. If you want to alert readers about the fact that a sail isn't as much like a barn door as people assume, I suggest pulling the "in essence" statement and adding a new, short, paragraph summarizing the wing-like and door-like behavior of sails. Isaac Rabinovitch (talk) 12:02, 17 September 2010 (UTC)
 * But in my opinion the statement is objectively true and I don't really see how to improve it. Nevertheless, I would welcome specific suggestions for new text.--Gautier lebon (talk) 11:02, 18 September 2010 (UTC)

Thrust?
Dear Swordfish,

Where in the sail aerodynamic literature  is  the  term "thrust" used? For example, I  cannot find  it  in   CA  Marchaj's  work  except to refer  to force applied on fish fins. Bcebul (talk) 23:14, 8 June 2011 (UTC)


 * Thrust in the strict physics definition is basically any Force which results from Newtons 2nd and 3rd laws, so I think using the term is apt here. (Airplane propellers generate thrust by pushing air backwards.  Boat propellers generate thrust by pushing water backwards.  Canoe paddles generate thrust by pushing water backwards.  Sails generate thrust by pushing air backwards.)  OTOH, I have no particular affinity for the term and have no objection to the current recasting of the article to avoid the term.


 * Like all English words, "Thrust" has several meanings, and its narrow definition in aerodynamics as the force from the engines (see http://www.grc.nasa.gov/WWW/k-12/airplane/thrust1.html) may imply to some users that thrust only comes from engines. If this causes confusion on the part of some readers, then that's a good reason for avoiding the term. Mr swordfish (talk) 14:04, 9 June 2011 (UTC)


 * Reference the article and Sails generate thrust by pushing air backwards. referenced above. Sails do not generate thrust/lift by pushing air backwards (whatever that actually means!!). In very simple terms, thrust/lift is generated on a beat/reach by the difference in speeds of the airflow across the back of the sail compared with the airflow across the front of the sail. The speed differential creates a force called lift at c90 degrees to the sail. The centreboard/keel reduces the sideways component of the lift and the forward component of the lift provides forward motion. A boat sails faster on a reach than a beat because the lift generated by the sail becomes more parallel to the direction of the boat.  Standard terminology is that a wing or sail produces lift. Boatman (talk) 14:43, 9 June 2011 (UTC)


 * I would suggest reading the talk section under Lift where this argument has been done to death. Bottom line is that there are several ways to explain lift, none of which has a monopoly on truth. Since this is an article about sails (not lift) it is appropriate to use the simplest explanation of lift and give the reader a pointer to a more thorough discussion. Mr swordfish (talk) 16:14, 9 June 2011 (UTC)
 * Totally agree but the current simple statement '....the boat is driven forward as air is redirected backwards....' is completely incorrect.  Also the simple statement '....the sails acting as airfoils propel the boat by redirecting the wind coming in from the side towards the rear......' is also incorrect?? These explanations here are completely incorrect. Some work needs to be done here. (my preference is that it is done by others who have been involved in this discussion longer than I) Thanks Boatman (talk) 13:05, 12 June 2011 (UTC)
 * I guess people didn't see the comment that I posted under "sails as wings above". What I said was that we seem to be getting into a well-intentioned editing war regarding how to explain how sails work. As most of us know, there are many different possible explanations, all correct. Some people like to model a sail as a rigid wing, others don't like that model. May I suggest that we work out a consensus text on the talk page? The consensus text should be addressed to the average reader, who presumably does not know much about physics, and should give references so that interested people can learn more. The consensus text should also mention that there are different models and different theories, each of which has its pros and cons (just as light can be usefully, and correctly, modelled as waves or particles, depending on what you are trying to explain/predict).  Regarding Boatman's comment above, no, the statements are not incorrect, but they may confuse the non-initiate.  As Swordfish says, there are many ways to explain this, all correct, but some harder to understand than others.--Gautier lebon (talk) 07:10, 13 June 2011 (UTC)
 * Apologies, I did not know that there were different theories each with pros and cons as it all seemed very staightforward to me when I did my Maths degree (albeit a long time ago!!). I will leave it to you guys to develop a simple statement for the non-expert. Thanks, Boatman (talk) 10:15, 13 June 2011 (UTC)
 * Well, what is straighforward depends on what your starting point is. Increasing use of overlapping jibs led to the popularization of explanations derived from airplane wing aerodyanamics (as in the slot effect).  May I request that you post here your straightforward explanation from the old days, we can then work on that to develop consensus text?--Gautier lebon (talk) 07:44, 14 June 2011 (UTC)

Does sail plane (glider) theory deal with "thrust" except when talking about take off engines? Bcebul (talk) —Preceding undated comment added 23:18, 8 June 2011 (UTC).

Well, I came in this morning with all the references needed to propose a consensus text. But first I looked at the current text of the article and I find that it is fine: the section on Sail seems to me to be just fine as it stands. I looked through the article, and I could find only one use of "thrust". I have replaced that with "driving force". So I don't think that any further edits are required.--Gautier lebon (talk) 10:54, 16 June 2011 (UTC)
 * Are you 100% sure that this statement is correct: the boat is driven forward as air is redirected backwards.  Thanks, Boatman (talk) 16:01, 16 June 2011 (UTC)
 * Yes, that is the simplest way to describe how any aerofoil works: aircraft go up and then stay in the air due to the mass of air being continuously deflected downwards by their wings. In the same way, on any point of sail, if the boat is being driven forward by the sails, some amount of air is being captured in their curves and is being moved to some point further aft (relative to the boat) all the time. All this is well explained in a number of ways at Lift (force), but this by far the easiest to explain without mathematics or the use of any other physics theory. Each cubic foot of air that was deflected by a sail keeps moving on downwind away from the boat, but it does so further 'aft' than it would have been if the sails hadn't been there. It may well be further to port or starboard too (with reference to the boat's 'coordinates'). The point about being further aft is that the air has mass, and so the force needed to move it aft is left with the boat, and moves it forward. Especially after the keel and underwater shape take care of the sideways forces, so we get the squeezing-the-soap, or the cherry-pip, effect when sailing on the wind. --Nigelj (talk) 16:41, 16 June 2011 (UTC)
 * A sail acts like a plane's wing. The aerofoil shape of the sail causes the airflow to flow faster on one side of the sail than the other causing an effect or force at appoximately 90 degrees to the sail known as lift. The sideways component of the force is nullified by the centreboard/keel resisting sideways motion of the boat and the forward component of the force pushes the sail and hence the boat forward. When sailing on a beam reach the sail is at approximately 90 degrees to the boat so most of the lift is parallel to the boat and 100% utilized to push the boat forward.  A boat sails more slowly when sailing close hauled with the sail at an angle of approximately 40 degrees to the boat because most of the lift is now trying to push the boat sideways reducing the amount of lift available to push the boat forward. To me summarizing this as the boat is driven forward as air is redirected backwards leads me to think the principle has similarities to a Florida air boat which I don't think it does!.  For me the description I drafted above with appropriate tweaks is of encyclopedia quality and accuracy and undserstandable to the layman. What do you guys think? Thanks, Boatman (talk)
 * The main difference in your description ("The aerofoil shape of the sail causes the airflow to flow faster on one side of the sail than the other") is discussed at Lift (force). The explanation I have given is related to what that article says at Lift (force). It's true that it goes on there to say, "The theory, while correct in as far as it goes, is not sufficient to allow one to do engineering". In this article we want only to get the idea across, not to teach people to 'do engineering' and calculations. Reminding readers of a bit of 'school science' that is actually wrong, without needing to have mentioned it (and without the time or the space here to explain all the complexities) is counter productive when we link to the full descriptions anyway. What do others think? --Nigelj (talk) 22:15, 16 June 2011 (UTC)


 * Nigel, I think you have it basically correct. Mr swordfish (talk) 16:36, 17 June 2011 (UTC)


 * boatman:  To me summarizing this as the boat is driven forward as air is redirected backwards leads me to think the principle has similarities to a Florida air boat which I don't think it does!.  


 * Actually, the principles behind how an airboat moves and how a sailboat moves are  basically the same. If a sailboat were to somehow accelerate forward without some other mass being simultaneously accelerated backwards this would constitute a violation of the law of conservation of momentum. Saiboats are not magical vessels that obey their own laws of physics, rather they follow Newtons laws and conservation of momentum just like rockets, rowboats, baseballs, airboats, etc.  Just like everything else in the known universe, in order to move forward a sailboat must push something else backwards.


 * Anyone who regularly races sailboats knows about "dirty air" behind and to leeward of another boat. Frank Beckwaith's High Performance Sailing shows that the airflow in the vicinity of a typical racing sloop is deflected by about 5 degrees and slowed by about 5%.  That's why you can't point as high or go as fast when another boat is ahead and to windward - the deflected air is a very real and noticeable phenomenon.


 * boatman: The aerofoil shape of the sail causes the airflow to flow faster on one side of the sail than the other...


 * The problem that I see with this explanation is that it's not at all clear why the airflow is faster on one side than the other. In all my research, I've yet to see a simple and correct explanation of why the airflow is faster on one side than the other.  Either the explanation involves the discredited Equal Transit Time Fallacy (simple but wrong) or it involves solving partial differential equations and applying boundary conditions to obtain a vector field representing fluid flow (not at all simple but correct).  If someone can come up with a simple and correct reason for the speed difference I'd be happy to use that explanation.  For a general interest article I don't think we should be burying the reader in advanced calculus, nor should we be giving an explanation that is incorrect.  The alternative, if we're going to base the explanation on speed differences, is to just state that they are there without saying why - but this is not very satisfying and closer to magic than science.


 * Thus, since we seem to be unable to simply explain lift via speed differences and pressure differences here, we should just present the simple explanation and point the user to the more thorough treatment at Lift(Force) Mr swordfish (talk) 09:15, 17 June 2011 (UTC)


 * As I've said before, there are different ways to model this mathematically, and different ways to explain those models in words. All are correct, but some are eaiser to understand than others.  I agree with Nigel, the current explanation is simple and correct.  I also agree with Swordfish: those who wish to know more can go and read the cited articles.  To Boatmans point: in my experience, more people are confused than enlightened by the differential airflow and "sucking the boat forward" models.  I think that the plain old Newtonian action-reaction model is easier to understand for the non-initiate.--Gautier lebon (talk) 14:29, 17 June 2011 (UTC)


 * Gautier, while I am in general agreement with your comments here, I have to take exception to the assertion that "all are correct". In fact, there are several "theories" that are not correct, for instance the Equal Transit Time Theory. Unfortunately, this incorrect explanation appears in many tertiary sources (schoolbooks, museum displays, encyclopedias, etc) and is perhaps the most prevalent and common explanation out there.  It's not the place of this article to debunk it however, so I don't think we have a substantive disagreement. Mr swordfish (talk) 16:36, 17 June 2011 (UTC)


 * What I am trying to do here is have a simple sentence(s) which explains to a non-sailor non-mathematician layman how a sail generates forward motion for the boat The article says:- In accordance with the law of conservation of momentum, the boat is driven forward as air is redirected backwards. This driving force is called lift and the redirected air is called downwash.. I will now read the above as a layman. The two sentences say to me that the boat is driven forward as air is directed backwards - OK, the redirected air is called backwash - OK so the 'thing' that drives the boat forward is called backwash, the driving force is called lift - Confused now because I thought the message was that the boat is driven forward by redirected air called backwash. Please reply as if to a layman as for me this is the best way forward.  Thanks for all your constructive comments above. Boatman (talk) 14:46, 17 June 2011 (UTC)
 * Any thoughts on the query that I outlined above? Thanks Boatman (talk) 16:52, 19 June 2011 (UTC)
 * Swordfish: you are of course correct, not all of the published explanations are correct. Boatman: I see your point.  How about shortening the current text, so that it simply reads: "The other way sails propel the boat occurs when the boat is traveling across or into the wind. In these situations, the sails acting as airfoils propel the boat by redirecting the wind coming in from the side towards the rear. This redirection results in force on the sails (sometimes called lift) which can be used to drive the boat forwards.[7][8]"--Gautier lebon (talk) 08:24, 20 June 2011 (UTC)


 * Gautier, I agree that shortening the text as you propose would improve the article, however I think we should cite either conservation of momentum or Newton's action-reaction to explain why air being redirected implies a forward force. For instance, something like:


 * "The other way sails propel the boat occurs when the boat is traveling across or into the wind. In these situations, the sails acting as airfoils propel the boat by redirecting the wind coming in from the side towards the rear. In accordance with the action-reaction law this redirection results in force on the sails (sometimes called lift) which can be used to drive the boat forward.[7][8]"


 * Mr swordfish (talk) 15:19, 20 June 2011 (UTC)
 * I support Swordfish's proposal. Boatman: what do you think? Does this address your concern?--Gautier lebon (talk) 07:07, 21 June 2011 (UTC)


 * Upon reflection and a bit of research, I'm hesitant to invoke the action-reaction (Newton's 3rd) law here. While it's a correct usage, readers may think we are invoking the "skipping stone" theory as discussed at  http://www.grc.nasa.gov/WWW/k-12/airplane/wrong2.html and this may cause some confusion or calls for further edits.  I propose we go back to the Conservation of Momentum explanation that's been on the page for 5 years now (until recently).


 * "The other way sails propel the boat occurs when the boat is traveling across the wind or into the wind.  In this situation, the sails propel the boat by redirecting the wind coming in from the side towards the rear.  In accordance with the law of conservation of momentum, air is redirected backwards making the boat go forward. This driving force is called lift". 


 * Mr swordfish (talk) 14:03, 21 June 2011 (UTC)


 * This is also OK for me.--Gautier lebon (talk) 07:04, 22 June 2011 (UTC)
 * hi,
 * i had same issue on wp:fr, so i create a specific article on this : effort sur une voile.
 * i agree with a simple explanation that could be not exact, and you could add a redirection on a more detail wikipedia article Forces on sails for example.
 * best regards Erwan1972 (talk) 08:34, 22 June 2011 (UTC)

Frequently on the NASA 'wrong' pages linked above, they mention 'flow turning'. There is a page about it at http://www.grc.nasa.gov/WWW/k-12/airplane/right2.html. I think there is a big difference between understanding that something happens, and understanding the mathematical model that describes why it happens. If you put your hand, palm-down, out of a car window and rotate your wrist, you do not need differential equations, Bernouilly, or conservation of momentum, to tell you that your hand is pushed up and down by the airflow. It is similar for the forces felt if an oar is held vertically in the water from a boat and rotated either side of slicing through the moving flow. That's all we need to do here - avoid telling people anything that is mathematically wrong, while reminding them of the physical reality with which they are probably already familiar. Flow turning, or 'redirection of the wind', produces a force in practice. Why, and how much force is outside the scope of this article, as Erwan says. --Nigelj (talk) 14:41, 22 June 2011 (UTC)

Regarding the Sail aerodynamics section: I have been following this discussion and  making  edits  which I think  concur with the gist of the consensus about explaining sailing upwind or on a reach for  this  article. The ideas are to keep things simple and within the  article's scope while making  appropriate supporting and expanding links and not saying anything incorrect. It is a  challenge  not  to  mislead or  confuse the  reader. See the current text and my edit comments. I have found everyone's comments and edits most helpful. Bcebul (talk) 02:04, 23 June 2011 (UTC)
 * I am OK with the current text, or with the following simplified version: "The other way sails propel the boat occurs when the boat is traveling across or into the wind. In this situation, the sails propel the boat by redirecting the wind coming in from the side towards the rear. In accordance with the law of conservation of momentum, air is redirected backwards making the boat go forward. Air pressure differences across the sail area result in forces on sails including drag and lift; a component of the lift is the main driving force.[7][8][9]."--Gautier lebon (talk) 08:54, 23 June 2011 (UTC)
 * "...as the boat goes forward..." is more correct because the sail "makes" the air go back AND/WHILE the air "makes" the sail go in an opposite way as per Newton and equal/opposite transfer of momentum.  What  "causes" this   transfer is  beyond  this  article. But "air pressure differences" and  links  to in  depth  physics point  the  way. The boat  actually heels and  drifts as  well as going forward. Which is  why I wrote as I did. Your  last  phrase about  "...component of the  lift..." is   less  awkward than  mine. I  think  all  the  links  are helpful  to  the  reader. Bcebul (talk) 10:26, 23 June 2011 (UTC)


 * Thanks to all who have participated in this productive discussion, especially Gautier who suggested we proceed on the talk page and Bcebul who has made many positive contributions to the article. I'm in favor of Gautier's latest proposal - it says more or less the same thing as Bcebul's current (very good) version, but is a bit more readable and conversational. I also like the practice of moving the citations to the end of the paragraph - they're less distractive when they're not in the middle of the prose.  If there are no objections, I'll edit the article to accomodate that change.  Mr swordfish (talk) 14:04, 23 June 2011 (UTC)
 * Bcebul: indeed the "lift" also engenders heel and drift; as you say, your sentence was correct, and I thank you for your compliments on my rephrasing. All: I think that we can give ourselves a collective pat on the back for what is, in my opinion, a textbook example of how to work cooperatively to improve Wikepedia.  I would like to thank all involved.--Gautier lebon (talk) 06:55, 24 June 2011 (UTC)

Introductory definition
The first sentence of this page is unhelpful, and I feel a more readable imtroduction would be useful. As it is, it reminds me of the Dickensian horse, " Quadruped. Graminivorous. Forty teeth, namely twenty-four grinders, four eye-teeth, and twelve incisive. Sheds coat in the spring; in marshy countries, sheds hoofs, too. Hoofs hard, but requiring to be shod with iron. Age known by marks in mouth.' Thus (and much more) ". Arrivisto (talk) 22:35, 31 August 2012 (UTC)

recent changes to sail aerodynamics section
The differences can be seen here: https://en.wikipedia.org/w/index.php?title=Sail&diff=593265260&oldid=590826912

I do not find that the edits, taken as a whole, improve the article. In particular, the first sentence "Air viscosity, acting parallel to the sail surface, and air pressure differences acting perpendicular to the sail surface are related to aerodynamic" is difficult to parse and doesn't seem to advance the article. Other opinions? Mr. Swordfish (talk) 17:14, 31 January 2014 (UTC)


 * I agree with Swordfish.--Gautier lebon (talk) 13:51, 1 February 2014 (UTC)


 * Seeing no disagreement, I'm going to revert the changes. Mr. Swordfish (talk) 18:35, 6 February 2014 (UTC)

Recent unexplained mass deletion of material
New user D1ggg has recently made a bunch of unexplained deletions. I have asked him or her to take it to talk since I don't understand the reasoning.

I'm undoing the changes. Let's discuss here and not get into an edit war. thanks. Mr. Swordfish (talk) 18:37, 26 October 2017 (UTC)
 * I don't know every styling detail but I know this one:
 * "As a general rule, the "See also" section should not repeat links that appear in the article's body or its navigation boxes" - MOS:NOTSEEALSO
 * That's why duplicate links were removed.
 * Duplicate links often against MOS:DUPLINK D1gggg (talk) 23:17, 9 November 2017 (UTC)


 * Agreed. . A simple note explaining that the edit involved removing duplicate links would have been helpful.  Edits that without an explanatory note invites reverting - those of us with hundreds of articles on our watchlist don't always take the time to review unexplained edits.  See WP:ES.   Mr. Swordfish (talk) 12:41, 10 November 2017 (UTC)

Moveable sails
The reference on the section "Movable sails" does not seem very expert. The information does not make sense. Something on Kite rigs may belong here, if User:HopsonRoad agrees, but unless this section can be re-written and re-sourced to make sense, it needs to be removed. HLHJ (talk) 05:19, 27 November 2017 (UTC)
 * I concur with your assessment, HLHJ. Clearly Egyptian sails could move well before the date cited. Also, the source cited does not appear to be reliable—it's a puff piece. As to kite rigs, they are mentioned in the lead as being beyond the scope of this article, but have two links to take the interested party to that topic. Thanks for discussing this matter here, first, before deleting a good-faith contribution Cheers, User:HopsonRoad 14:56, 27 November 2017 (UTC)

Genoa jib Legend
If I have understood it correctly, but I am not native in English, the legend of the Genoa Jib, which now is in a section of the page after "See also", is not in the correct order. For example in the Clew in the figure is number 12, but in the legend is number 10.

In the page Genoa (sail) the same figure seems to have the correct legend (with some different wording).

Also it could be better to have the legend just below the figure instead in a far away section.

Can someone with better knowledge in the subject fix it, or should I do it myself? --AnyFile (talk) 19:53, 12 March 2022 (UTC)


 * Agree that the legend should be right under the picture rather than having to click away to read it. Not sure how to fix, but it should be fixed. If no one gets to it soon I'll give it a try. If you know how, go for it.
 * As for whether it's mislabeled, let's put it next to the picture so we can easily see and go from there. Mr. Swordfish (talk) 22:46, 12 March 2022 (UTC)


 * I checked each number on both drawings against both legends. They correspond. In the Genoa article, the numbers aren't consecutive in the legend, because they are grouped by edge or corner of the sail. The numbering in Genoa is confusing as to what number belongs to what label.
 * As to whether the legend should be in the body of the image or not, here are three considerations:
 * The image is intended to illustrate cross-cut construction, not to be a detailed guide to every part.
 * Adding the legend within the body takes up a lot of real estate, crowding out images in lower sections.
 * For those wishing to see the nomenclature that corresponds to a number, the legend appears by mousing over the word "Legend" on my browser and by touching the word on my tablet, obviating the need to cross-check between sections. Mr. Swordfish, AnyFile does the mouse-over feature not work on your platforms?
 * HopsonRoad (talk) 00:30, 14 March 2022 (UTC)
 * Yes, the mouse over displays the legend, but it covers up the picture so it's hard to use. Also, I'm not sure how many users know to use the mouse over functionality. I'd advocate for an old-fashioned legend that's simple text under the picture, but don't feel strongly enough about it to do the edit myself.
 * If the image is intended to illustrate cross-cut construction, perhaps we can find a better image without all the numbers. That would seem to solve the problem. Mr. Swordfish (talk) 20:39, 15 March 2022 (UTC)
 * That's a good idea to look for alternative images. I looked in the Jib, Genoa and Mainsail Categories in Wikimedia Commons and didn't find anything remotely suitable. HopsonRoad (talk) 21:30, 15 March 2022 (UTC)
 * I went with a cross-cut/bi-radial/tri-radial comparison. More appropriate and less confusing for this section. Thanks for highlighting this problem! HopsonRoad (talk) 00:37, 16 March 2022 (UTC)

Proposed merge of Bunt (sail)
The article Bunt (sail) is a short dicdef which I propose would be better served being incorporated somewhere in this article, with an appropriate section redirect. Cheers! BD2412 T 13:42, 15 August 2023 (UTC)
 * I've looked at ways to merge this material but we already have a reasonable amount of this info at Clewlines and buntlines, with more recent references. What do you say to just a straight redirect to that page? -- Euryalus (talk) 07:49, 25 October 2023 (UTC)
 * Pinging as creator of the "Bunt" article, as they're still active and might have a view. -- Euryalus (talk) 07:51, 25 October 2023 (UTC) :: No objection. I leave it to the subject-matter experts to determine the most appropriate resolution. Cheers!  BD2412  T 13:37, 25 October 2023 (UTC)
 * Since both Bunt (sail) and Clewlines and buntlines have just one reference between them, with that reference not confirming much of the article content, it seems counterproductive to merge them. (Frustratingly, Clewlines and buntlines is a rather good explanation of the subject.) If we were starting from scratch, it would make sense to have a master article to which all these defined components could be directed. The obvious one is Square rig, but that article is deficient in that it hardly says anything about a very large subject. What we don't want is for Square rig to end up as an unplanned accumulation of stuff. There are many sources to bring together for a revision of that article, so there is no overnight solution here.
 * In the short term, Bunt (sail) could simply be pointed at Glossary of nautical terms (A–L) – which at least does have a reference (which I have not checked, yet). ThoughtIdRetired (talk) 19:02, 25 October 2023 (UTC)

An unreferenced part of the article
Types of sail that can be part of a sail plan can be broadly classed by how they are attached to the sailing craft:... and its associated following text is unreferenced. The immediate problem is the statement that jibs are fastened to a stay. Whilst that is true on many modern yachts, it is not universally the case on older vessels, nor on modern-built craft of a traditional type. Jibs may be set flying, especially when set from the end of a bowsprit or jib-boom. (Looking quickly for a reference showing a jib set flying in a modern, plastic-hulled, Bermuda-rigged vessel, I find a Wayfarer (dinghy) set up for cruising with a genoa rolled on the forestay and a smaller jib which is set flying in stronger winds: The Dinghy Cruising Companion by Roger Barnes, pg 126.) That calls into question the validity of the rest of the text. I question how common the categorisation of sail types is. Hence, it would be nice to see a reference. At a minimum I would question whether the categories even work. Where, for instance, would you put gaff rig? The sail is set with a spar at its head and is fastened to a mast. The spinnaker seems to be simplified to just how its head is supported, completely ignoring the need for a spinnaker pole. Overall, it just does not seem to come together as a satisfactory explanation. ThoughtIdRetired (talk) 10:12, 30 October 2023 (UTC)


 * Your concern is valid, User:ThoughtIdRetired. I have attempted to address the problematic claim of a "classification" for which I take blame. What's left relies on the content of the blue-linked articles for validation. See if this is a useful cure. Cheers, HopsonRoad (talk) 22:37, 30 October 2023 (UTC)
 * Thanks for your attention to this. The only immediate thought is that a spritsail is attached more to the mast than to the sprit. See or . It is certainly unlike lateen or a dipping lug, where there is no connection between the sail and the mast. I am not sure where a standing lug would feature in this classification system, as that relies (for efficient operation) on a tack downhaul which is generally fastened to the foot of the mast. (A reference for that is, much to my amusement, Swallows and Amazons – the book itself, not the article herein. More serious references are available.)
 * And just to be extreme with the nit-picking, this part of the article is unreferenced. Whilst it is now a relatively reasonable description of how things work, I am not sure it is down to Wikipedia to invent a classification system. Is there a reference available for this system – even if it is not immediately to hand? ThoughtIdRetired (talk) 14:13, 31 October 2023 (UTC)
 * Here is a picture that clearly shows a spritsail laced to the mast ThoughtIdRetired (talk) 14:18, 31 October 2023 (UTC)

Problem statement
The article states: The square rig is aerodynamically most efficient when running (sailing downwind). This really perpetuates a common misconception.

First, the reference for this statement: Sloop of War, pg 288. According to Amazon, this book only has 256 pages – so the page number immediately looks wrong. I have an electronic version of this book (without print edition page numbers) and various searches do not reveal anything to confirm the statement in the article. (There is some discussion about the problem of balance with two masted square rigs, but that is as close as I can get to finding something relevant.) I am not saying the source does not support the article, but it certainly needs checking.

Second, the general principle. When the two rigs, fore-and-aft and square, are compared, it is important to compare similar hull shapes, sizes and, most importantly, dates. The fact that a modern fore-and-aft rigged high performance yacht sails better to windward than a 19th century square rigger with natural fibre sails, a bluff-bowed hull and either a large cargo or lots of heavy guns is, at best, unhelpful. We do not have modern square riggers, so the comparison has to be historic. For that we have the opinion of James Cook and Frederick Marryat (who, as following reference states, is taken to be an RS on ships of that era by maritime historians). Both thought that a brig had better performance than a schooner, including to windward. This is a view that was widely held. It is discussed in a book review, where the reviewer (reasonably emphatically) supports the author's view to this effect. To explain further, it is not so much that one rig was better than the other to windward, it was that fore-and-aft rig was not very good for long downwind passages. Firstly you got a lot more chafe with fore-and-aft. Then there was the ever-present risk of an unintended gybe. (Those who sailed the huge multi-masted schooners lived in terror of this.)

Thirdly, the exact article content is plain wrong as square rig is actually at its most efficient when reaching (?just like for-and-aft?). This is because you get the least amount of blanketing of the various sails. I would hope the aerodynamics is pretty obvious.

Does anyone want to make a case for what the article's reference says before this is fixed? ThoughtIdRetired (talk) 22:16, 1 January 2024 (UTC)


 * I concur. The link to the reference includes no statement, supporting the claim. Unless there is a reference that discusses efficiency of the rig on various points of sail, I recommend that the entire sentence be removed. Any discussion of efficiency of sails on various points of sail should encompass a range of sail types, be discussed in the body of the article (not solely the lead section) and be supported. by references. Cheers, HopsonRoad (talk) 15:21, 2 January 2024 (UTC)


 * Comment from User:HopsonRoad noted and largely agreed. However, this is not the lead, but the section after the lead which seeks to separate sails into two categories: square rig and fore-and-aft rig. So the difference between the two does need to he covered in the article. It is simply a case of coming up with a concise explanation based on some good quality references. So there is a little bit of homework to do there before making any changes. ThoughtIdRetired (talk) 14:06, 6 January 2024 (UTC)


 * I have gone ahead and removed the seriously wrong statement from the article. This section is the place to explain the differences between square and fore-and-aft rig, which needs sourcing. ThoughtIdRetired (talk) 14:10, 6 January 2024 (UTC)