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Old 03-11-2012, 00:00   #1
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Sails use apparent wind?

In close reach, sails are using apparent wind, correct? So you can sort of rely on the masthead fly?
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Old 03-11-2012, 00:12   #2
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Re: Sails use apparent wind?

Sails use apparent wind at *all* points of sail. That's sort of the definition of apparent wind: it's the wind relative to the boat. The masthead windex is the proper indicator, although the wind isn't always uniform from sea-level to mast-top.
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Old 03-11-2012, 00:18   #3
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Re: Sails use apparent wind?

The windex is a good start to get the sails set. Once you've gotten on your course you adjust the sails, "dial them in" by watching the sails themselves. The tails are great indicators that can show you how the wind changes from high to low.
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Old 03-11-2012, 04:11   #4
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Re: Sails use apparent wind?

Apparent wind is the only wind for trim. Once moving true wind does not matter.
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Old 03-11-2012, 05:56   #5
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Re: Sails use apparent wind?

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Originally Posted by darsunt View Post
In close reach, sails are using apparent wind, correct? So you can sort of rely on the masthead fly?

"Apparent wind" is every bit as "real" as what mother nature is providing. The simplest way to understand apparent wind is to get on a bike and ride. No matter what direction you ride, you will feel "wind" in your face. Unless you are riding directly into Mother Nature's wind direction, it is apparent wind you feel -- although Mother Nature's wind is still affecting you. You feel it because you are moving faster than the wind. If you're riding DDW at 10 mph and the wind is 10 mph, you won't feel any wind, but if the wind is 5 mph it will feel like 5 mph wind "on your face." Most sailboats can't go faster than Mother Nature's wind DDW, so the air will seem to be still. Great on a cold day but can be miserable on a hot day because any kind of wind on a hot day helps evaporate your perspiration, and hence, cools you off.

The wind indicator at the top of the mast helps you tack by pointing into "mother Nature's wind." (the wings on either side give you a pretty good idea of where to stop and start your tack -- you start with the arrow at one wing, and stop when the arrow has crossed to the other wing).

Apparent wind can confuse you when you're tacking. I don't have a wind indicator, but I can tell from the feel on my face where it is. I've just developed that feeling for true wind and have no trouble tacking. If you don't have a wind indicator you have to develop that feel for true wind, or you'll tack like a crazy person.

But unless you're tacking or absolutely DDW, your boat is responding to apparent wind.
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Old 03-11-2012, 06:47   #6
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Re: Sails use apparent wind?

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Originally Posted by Rakuflames View Post
The wind indicator at the top of the mast helps you tack by pointing into "mother Nature's wind."

But unless you're tacking or absolutely DDW, your boat is responding to apparent wind.
True and apparent wind can get confusing even without considering true and ground wind.
What is felt on the boat, sails, crew or wind indicator at the top of mast is always apparent wind. No exceptions.
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Old 03-11-2012, 07:50   #7
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Re: Sails use apparent wind?

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In close reach, sails are using apparent wind, correct? So you can sort of rely on the masthead fly?
Yes the masthead will tell you the apparent wind. But it wont tell you if your sails are working efficiently. IMHO telltales on the Luffs and Leaches are more important that any masthead vane. (disclaimer- except for running and broad reaching when the tales wont be working.)
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Old 03-11-2012, 15:53   #8
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Re: Sails use apparent wind?

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IMHO telltales on the Luffs and Leaches are more important that any masthead vane.
BINGO! Telltales are what you really need, to understand what is happening to the wind that is passing on either side of your sail.

Just one small disagreement, ozskipper... My opinion is not the least bit humble!
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Old 03-11-2012, 16:00   #9
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Re: Sails use apparent wind?

Sails use true wind, the boat's motion is apparant. errr,.... maybe it's a relativity issue! If you raise the sails tied to the dock... are the sails seeing apparant wind..?
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Old 03-11-2012, 16:33   #10
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Re: Sails use apparent wind?

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Sails use true wind, the boat's motion is apparant. errr,.... maybe it's a relativity issue! If you raise the sails tied to the dock... are the sails seeing apparant wind..?
The answer is yes, it's just that the induced wind vector is zero in that case, so apparent wind = true wind.
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Old 04-11-2012, 02:30   #11
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Quote:
Originally Posted by darsunt
In close reach, sails are using apparent wind, correct? So you can sort of rely on the masthead fly?
What is prompting this question?

The backstory is always interesting...
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Old 04-11-2012, 03:39   #12
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Re: Sails use apparent wind?

The only times the masthead vane is misleading as to the direction of the apparent wind are too subtle to worry about

(one is differential velocity with height - strength and/or direction, as implied by post #2
the other is the effect on the apparent wind of rolling. This induces a cyclical swing in the apparent wind which increase steadily up the rig, to a maximum at the masthead - so the vane exaggerates the apparent effect)

However, even setting this aside:

as most others have said, telltales on the sail are (once you get used to their peculiarities) better guides than the vane to the exact interaction of the sails with the wind.

early on, though, the vane helps a lot with making sense of what the telltales are telling you.

An easy rule of thumb regarding using headsail telltales to dictate your helming, when sailing hard on the wind at almost the right angle, with the sail correctly trimmed:

turn the boat (gently!) so as to present more wind to the side of the sail on which the telltales are not streaming nicely. The aim is to have them streaming nicely on both sides, most of the time.

PS: 1 more vote for sails NEVER see the true wind, unless you're tied to land. When you're moving, they see the true wind direction only when you're pointing the boat's bow or stern directly at the wind. (assuming no cross tide, for any pedants reading this!)
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Old 04-11-2012, 03:53   #13
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Re: Sails use apparent wind?

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Originally Posted by denverd0n View Post
BINGO! Telltales are what you really need, to understand what is happening to the wind that is passing on either side of your sail.

Just one small disagreement, ozskipper... My opinion is not the least bit humble!
Lol.. thats ok. Youre welcome. :-D
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Old 04-11-2012, 03:58   #14
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Re: Sails use apparent wind?

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Originally Posted by ozskipper View Post
Yes the masthead will tell you the apparent wind. But it wont tell you if your sails are working efficiently. IMHO telltales on the Luffs and Leaches are more important that any masthead vane. (disclaimer- except for running and broad reaching when the tales wont be working.)
One other thing, the Vane is subject to is the inertia of the boats movement in lighter winds, this means that if the boat is hit by waves, it will respond erratically. making it even less important.

In very light to calm conditions, when even the telltales wont work, your best friend is a smoker (there i said it). Cigarette smoke will never go directly up when outdoors- it will always be affected by the lightest zephyr- even if the day appears totally calm.

< smiles and lights up >
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Old 04-11-2012, 04:13   #15
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Re: Sails use apparent wind?

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Originally Posted by Andrew Troup View Post
PS: 1 more vote for sails NEVER see the true wind, unless you're tied to land.
If we are going to be pedantic, and why not its an Internet forum
When tied to land the sails will see apparant wind "ground wind" not true wind. ( unless the current is zero)
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