Point of Sail
- Thread starter charliegrau
- Start date
Your boat speed is much more limited when sailing close hauled. You don't change course...you control boat speed. Use your tell tales and the compass. Head up till the windward tell flutters and then back off... the boat will slow down... your compass course will deviate 5 degrees either way... but your average course will stay at 315..... if you notice it changing.... to 320 for example.... true wind direction is shifting... you're in a lift.
I'm hoping I didn't read this incorrectly... didn't you mean to say "as the true wind speed builds?" The apparent wind direction moves aft as the true wind speed increases.
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Yep.
As you note, changes in apparent are much more complex because it is a 2nd order effect that also involves boat speed.
When the breeze increases with the same angle, the boat benefits from a 'velocity lift', even thought the angle did not change.
More important to note is when the breeze falls off while this angle does not change; the resulting velocity header (made worse by the boat moving faster that the current breeze would allows) often has newer sailors tack into the true header. Honor the knock and adjust to the new breeze.
I'm not forgetting...I disagree. In my experience if the apparent wind is forward of the beam, then it moves farther forward and increases as boat speed increases. If the apparent wind is abaft the beam, it moves aft and decreases as boat speed increases. In either case, I have to adjust my sails as the changes occur.
My boat can't see true wind...it only sees the net effect of true wind, set and drift, leeway, which manifests as apparent wind. True wind obviously has an effect, and has to be considered to determine your heading, taking into acount the boat's sailing characteristics, current, obstacles, crew comfort, waves, etc.
I always trim my sails to apparent wind. What other methods are there?
I do agree that boat speed can improve you pointing ability because of lift from the keel and rudder. That may account for your decreased angle as speed increases. When you are going from 44deg to 36deg in relation to true wind as true wind increases, how is your apparent wind affected?
You're just looking at it wrong.
You say:
How did that happen? The boat is getting faster. True wind must have come UP.
If you are close hauled in say 6 knots. 44 True wind angle. 4 knots boatspeed.
Wind comes up to 10. Apparent shifts AFT.
East sails to match the aft breeze.
Turn UP to match the new wind.
Trim in to harden up again.
Now you are sailing at 6 knots, true wind angle 41 degrees. Apparent wind even tighter.
None, that's what you should do. But HOW and WHERE they end up is a function of TRUE wind.
More boat speed generates more lift and yes that helps windward ability against TRUE. The better your keel and rudder the more help you get.
But when the true wind INCREASES, the apparent wind goes AFT. You can head up. Its a fundamental part of sailing. Plug numbers into the apparent wind calculator.
http://www.sailingcourse.com/keelboat/true_wind_calculator.htm
I've been following this thread and, wow, it has legs. So, to summarize the relevant point here, I would say that you will have difficulty in distinguishing a velocity lift from a wind shift lift if you rely on the apparent wind. Either looks the same to the tell tails. The velocity shift calls for the ease, head up, trim response for optimum performance. The real wind shift lift doesn't. Since the wind velocity remained constant you merely follow your tell tails to a course more directly towards destination (Mark.) So you trim sails for the apparent wind but your response to a lift, or a knock, depends on the true wind. Is that a fair statement?
I would say the relevant point here is:
You trim to apparent, but you always sail in true.
Full stop. TRUE wind is your horsepower. And it determines where you can go. Where you do go, and what sails you choose 'creates' your apparent.
Now, noting a velocity shift (or header) is only important if you are trying to makes absolutely best progress to windward (racing?) by staying on the lifted board. In any case you always sail to your telltails, but if you are trying to track true mean wind direction it helps to know why a lift or header happened.
I used your calculator and it showed that when the boat speed increased from 4 to 6 knots, the apparent wind moved forward....if you just change boat speed and keep wind speed and direction constant. Of course you change the equation if you add in changes to other variables such as wind speed or direction.
As I accellerate from a tack, my boat speed increases and apparent wind increases even if true wind remains constant. Sometimes in lighter winds I will fall off a little bit after I tack to build up boat speed and apparent wind speed as I pinch back up wind.
I pulled some excerpts from your post and added parenthetical comments/questions below:
"How did that happen? The boat is getting faster. True wind must have come UP."
(Not necessarily, my boat starts out at less than full speed and accellerates. As it gains speed, apparent wind changes.)
If you are close hauled in say 6 knots. 44 True wind angle. 4 knots boatspeed.
Wind comes up to 10. Apparent shifts AFT. (yes, if boat speed doesn't change)
East sails to match the aft breeze. (Not if I am working my way windward, I turn to windward and sail to the current trim of the sails, as in your next two steps.)
Turn UP to match the new wind.
Trim in to harden up again.
Now you are sailing at 6 knots, true wind angle 41 degrees (why is it now 41 vice 44 degress..did the wind shift?). Apparent wind even tighter. (as you say, apparent wind "tighter" due to increased boat speed....that's what I said...so where's the disagreement?)
As I accellerate from a tack, my boat speed increases and apparent wind increases even if true wind remains constant. Sometimes in lighter winds I will fall off a little bit after I tack to build up boat speed and apparent wind speed as I pinch back up wind.
I pulled some excerpts from your post and added parenthetical comments/questions below:
"How did that happen? The boat is getting faster. True wind must have come UP."
(Not necessarily, my boat starts out at less than full speed and accellerates. As it gains speed, apparent wind changes.)
If you are close hauled in say 6 knots. 44 True wind angle. 4 knots boatspeed.
Wind comes up to 10. Apparent shifts AFT. (yes, if boat speed doesn't change)
East sails to match the aft breeze. (Not if I am working my way windward, I turn to windward and sail to the current trim of the sails, as in your next two steps.)
Turn UP to match the new wind.
Trim in to harden up again.
Now you are sailing at 6 knots, true wind angle 41 degrees (why is it now 41 vice 44 degress..did the wind shift?). Apparent wind even tighter. (as you say, apparent wind "tighter" due to increased boat speed....that's what I said...so where's the disagreement?)
Wind vane is all you need to know
When you look up at the wind vane you are seeing the apparent wind direction. That is what you set your sails to. Nothing else matters.
When you look up at the wind vane you are seeing the apparent wind direction. That is what you set your sails to. Nothing else matters.
Sure. If you are a POWERBOAT. Try it with the WIND changing speed. That's what happens to us sailors.
Try it with a constant true wind angle say 45. And a boat speed of 4.
Run it with a true wind of of 6 knots. Apparent Wind of 27.5 degrees.
Now re-run with a puff of 10 knots. Apparent wind goes to 32. AFT!
I can't believe I'm having this discussion.
This is why every sailor should be required to start sailing in dinghys. You learn this FAST, or you get wet often. In a puff, the wind goes aft. Ease sail. Turn up. Trim in.
Sheesh, I never disagreed with you regarding the effects of an increase in wind speed. I merely stated the effect of changes in boat speed on apparent wind....and, yes, those changes would apply to a powerboat as well.
I'm not trying to be a hard case about this.
But you said:
That statement is overlooking how sailboats work at a very fundamental level.
Sailboats sailing to windward only speed up if the wind comes up. When that happens, the apparent wind goes aft. Now after than happens, the boat will speed up (slightly), and that moves the wind slightly forward. But never is the net change (breeze pushing it aft - boatspeed pushing it aft) result in the apparent going forward.
You have to remember that the apparent wind direction [and speed] is the vector sum of the true wind velocity (= speed & direction) and the boat velocity (also speed & direction). That is what vectors quantify (magnitude & direction). If the boat heading (direction) and true wind direction are not changed, the wind speed [increase] needed to push the boat faster along its course HAS TO BE GREATER than the boat speed at that time. So the vector sum will favor the true wind direction and cause the apparent wind to shift aft; even if the [sail] boat speeds up some.
Then with all due respect, you are doing the thread a disservice by thinking out loud.
The ONLY way your statement can be true is if the boat is:
1) Powered by a motor, or
2) Has first been hit with more wind, which as pushed the apparent wind aft.
I hoped this thread would educate people. Your attempt to 'explain' your statement is probably confusing them. Apparent wind going aft in breeze is a fundamental part of the physics of sailing. Why would you try and confuse that? My guess is that you didn't know, and are now trying to cover it up.
Maybe we need a refresher in vector algebra before discussing the physics of sailing?
I agree with you if you are starting with your boat up to speed. Once you are sailing pretty much as fast as the wind and conditions will allow, there is nothing to increase boat speed unless some additional factor comes into play. .. could be wind, could be current, could be starting your engine in order to achieve a desired course (or generate apparent wind). If you are just setting your sails or coming out of a tack with low boat speed, and have wind forward of the beam, the apparent wind moves forward as you accelerate. I'm not sure the wind has to be greater than boat speed, unless you limit the discussion to non-planing boats. The AC72's sail downwind at about twice true wind speed...."running" with sails trimmed as if close hauled. So much depends on conditions, boat characteristics. That's why I tried to keep my statement simple.
charlie, I think you're confusing the issue by dealing with coming out of a tack. Stay with Jack for awhile, he's right. ONLY consider what happens when you're already OUT of a tack and just ailing along. A puff hits. You have two choices:
1. Head up and LEAVE your sails just as they are
2. Maintain course and adjust your sails
Does this make it simpler?
1. Head up and LEAVE your sails just as they are
2. Maintain course and adjust your sails
Does this make it simpler?