Talk:Sail

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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)

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)

Contents

[edit] 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)

[edit] 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)#Common misconception. 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)

[edit] 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.

[edit] Diagram

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

[edit] 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)

[edit] 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)

[edit] 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)

[edit] 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)


[edit] 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)

[edit] 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)