If the wind is blowing hard enough to make a sailing vessel go really fast, then which way would the flag be blowing- ahead or behind?
assuming you mean wind blowing from behind. . .it depends on which is traveling faster.
boat>wind reverse
boat<wind forward
boat=wind not moving anywhere
chances are that the flag will be pointed somewhere to the side.
It would depend on the direction of the wind, and how closely the ship is sailing to the wind. Sailing ships don’t just sail with the direction the wind is blowing - the sails are rigged so the ship can sail at angles to the wind.
boat velocity>wind velocity, flag moves back
wind velocity>boat velocity, flag is forward
wind velocity and boat velocity are equal, flag falls down.
that chart was confusing as it stood
The flag would fly in the direction of the apparent wind*. This would be the direction of the wind as seen from the ship. Solving for this would be a maneuvering board problem, which I once wrote a description of for SingleDad (poster here last year). The information, which deals with plotting an intercept course, can be found at http://www.rpi.edu/intercept
Wind problems are kinda similar. Basically, it’s vector math.
[sub]* - Actually, it would be flying in the direction opposite the apparent wind, as wind direction refers to the direction the wind is coming from. Thus, a wind with a direction of north would blow a flag south. However, this way of looking at things seems rather backwards to someone who isn’t a sailor, I think.
My understanding is that sailing ships are fastest when the wind is blowing from the side - they can sail faster than the wind. So the flag would be pointing back and somewhat to the side.
Uh, that link should be: http://www.rpi.edu/~waterj2/intercept/
What waterj2 said - the flag indicates the apparent wind. Most sailboats have a little weather vane called a “windex” on top of the mast which also shows you the apparent wind, and is a great help, although you should be able to do without it. You trim sails according to the apparent wind, which makes sense when you think about it.
You can actually be moving over the water with an apparent wind from any direction except the “no-go” or “in irons” zone either side of directly into the wind[sup]1[/sup]. The windex usually has two little indicator posts for this region, just to warn you, though it’s only a guess, and if you point a small sailboat too far up into the wind, you find out damn quick anyway - they have a very abrupt transition from “close hauled” (heeled over sailing as close to the wind as you can) to sitting upright luffing.
“fastest when wind is blowing from the side” - when you are sailing at a 90 degree angle to the wind, you are on a point of sail known as a “beam reach”, and indeed, this is generally the fastest point of sail for a fore-and-aft rigged vessel. Old square-rigged sailing ships performed best on a “broad reach” - that’s with the wind coming from behind you at an appreciable angle (more or less DIRECTLY behind you is “running”).
Often, there will be very little apparent wind when running, since you are going in the same direction the wind is - nevertheless, this is where you want to REALLY be attentive to wind direction because of the danger of an accidental jibe should you cross the wind.
In the “close reach” and “close hauled” points of sail, where you are sailing at an angle against the wind, the apparent wind will have greater velocity than the true wind.
Some background: http://www.sailnet.com/collections/learningtosail/theory/index.cfm
[sup]1[/sup]The actual angle of this region will vary, but a good estimate for most small sailboats is that you can sail at about a 45 degree angle to the TRUE wind - this is convenient, because when you tack, you will change yuour heading 90 degrees and be pointed in a direction at a right angle to your current course. If you look at the angle on the region marked on the windex, it will be more like a sixty degree region, reflecting the fact that the apparent wind will be ahead of the true wind.
On an old time sailing ship, which I assume is what you are asking about, there could be flags and pennants flapping in all sorts of directions. This is because of eddies and wind breaks created by and right around the sails. For the most part the tall masted ships sailed better with a quartering wind, that is, with the wind blowing from the right or left of straight to the rear. If the wind were blowing directly from the rear, the sail at the back of the ship would block the wind from the more forward sails.
Thanks for the great answers (Sounds like some of you definitely have sea legs!) I hadn’t thought of wind hitting the boat from the side.