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Old 27-04-2010, 11:45   #1
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Wind Indicator: True or Apparent ?

Do you keep your instruments set to indicate true or apparent wind (especially when trying to make maximum windward progress), and how does the size of your "no-go" vector change in one versus the other? Been trying to deduce this while on the boat, as well as on paper, but can't seem to come to a conclusion on my own. thanks, pete
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Old 27-04-2010, 12:28   #2
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Apparent wind indications are closest to what you feel. If you started on small boats that has become an integral part of how you sail. True wind data is more valuable for fine-tuning your performance on a big, close-winded sailboat, but it may require you to re-educate some of your unconscious habits.

I don't race, and when I did it was on cats, so I bow to more precise knowledge soon to follow!
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Old 27-04-2010, 12:41   #3
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You can play with apparent vs true speed and direction using this calculator
True and Apparent Wind Calculator

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Old 27-04-2010, 12:49   #4
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I find apparent wind direction is the most useful most of the time. When the telltales are hard to see (night or whatever) the apparent wind direction tells me (1) if I'm roughly pointed in the right direction going upwind, and (2) if the sails are trimmed somewhere close to properly when off the wind (sailing a compass course or to a particular destination). Obviously the telltales give you the real story in either situation. Going straight downwind apparent wind direction warns of a potential gybe, or you can look at the masthead fly.

True wind direction can be useful for thinking about "grand strategy" for going somewhere, and it can also help for picking up windshifts over, for example, the course of an afternoon. True wind speed is nice for picking the headsail / desired reef before turning upwind at the end of a long downwind leg, and for telling your friends how hard it was blowing (without lying) when you get back in.
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Old 27-04-2010, 12:50   #5
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Thanks, I did start out on small boats (sailboards, the smallest, and everything from Lasers to Flying Scots), and I can quite easily calculate apparent wind using true wind and induced wind. That's really not my question, though. I am asking whether people who do have wind indicators on their boats find true or apparent wind to be a more useful metric, and asking opinions on whether the no-go zone appears to change (gets narrower or wider) when going from true to apparent. thanks again, pete
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Old 27-04-2010, 13:24   #6
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Sorry Kevkal: you must have been writing at the same time as I was! thanks for your response.
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Old 27-04-2010, 14:43   #7
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Quote:
Originally Posted by kevkal View Post
I find apparent wind direction is the most useful most of the time. When the telltales are hard to see (night or whatever) the apparent wind direction tells me (1) if I'm roughly pointed in the right direction going upwind, and (2) if the sails are trimmed somewhere close to properly when off the wind (sailing a compass course or to a particular destination). Obviously the telltales give you the real story in either situation. Going straight downwind apparent wind direction warns of a potential gybe, or you can look at the masthead fly.

True wind direction can be useful for thinking about "grand strategy" for going somewhere, and it can also help for picking up windshifts over, for example, the course of an afternoon. True wind speed is nice for picking the headsail / desired reef before turning upwind at the end of a long downwind leg, and for telling your friends how hard it was blowing (without lying) when you get back in.
Exactly what he said.

I have two wind instruments --a regular ST60 wind instrument and an ST60 close hauled wind gauge. If I'm beating, I keep the close hauled gauge on Apparent and watch that most of all. I will then keep the regular wind gauge on True for the sake of "grand strategy". On other points of sail, the other way around.

If you only have one wind instrument, then its natural state should be Apparent, for all the reasons stsated above.
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Old 27-04-2010, 15:03   #8
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Originally Posted by pete33458 View Post
Thanks, I did start out on small boats (sailboards, the smallest, and everything from Lasers to Flying Scots), and I can quite easily calculate apparent wind using true wind and induced wind. That's really not my question, though. I am asking whether people who do have wind indicators on their boats find true or apparent wind to be a more useful metric, and asking opinions on whether the no-go zone appears to change (gets narrower or wider) when going from true to apparent. thanks again, pete
Pete,
One issue on using true wind is that it requires that your instruments be carefully calibrated - course, speed and wind. On most boats this isn't true, so the true wind displays have a lot of error in them. I don't understand your question on the no-go zone. It is exactly the same for the boat whether you are looking at instruments in true, apparent or not looking at the instruments.

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Old 27-04-2010, 15:36   #9
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For working to windward you'll need good sail trim and then hold the apparent 'working' angle to make best VMG. Most of the time in the busy Solent it's hard to maintain the best course so I try to keep sail trim flexible, reducing tweaks to the required course rather than the wind.
On more open passages it's point the boat at the destination and trim to suit. Then sail to apparent wind angle for best boat speed on that heading. If course drifts off too much it's a case of re-trimming for the change of heading.
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Old 27-04-2010, 16:40   #10
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I don't understand your question on the no-go zone. It is exactly the same for the boat whether you are looking at instruments in true, apparent or not looking at the instruments.

Paul L
Yeah, this is kind of the issue, I don't think it is the same. I seem to be able to sail impossibly high (as in, like, 30 degrees off the wind using a low aspect ratio, negative roach, in-mast furling main sail) when I use the apparent setting; the true wind angle seems (roughly) as it should be. I can kind of understand this: if you're close reaching (for instance) on a starboard tack, the true wind vector should be aft of, and thus at a greater relative angle than, the apparent wind vector. I'm just trying to figure out roughly how much higher I can actually sail, or more accurately, how much higher to the apparent wind other people find they can actually sail (if this is the case). It just makes me nervous seeing that I'm sailing at 30 degrees to the apparent wind, you know, pinching and all that. pete
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Old 27-04-2010, 17:06   #11
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If you want to know how close to the wind you are actually sailing, then go close hauled on one tack and read the compass. Tack and go close hauled on the other tack, read the compass. Subtract the difference and divide by 2. That is the true angle that you are pointing (barring current) and including leeway.

Taking your example. Let's say you are seeing 30* apparent as close hauled. 12 knots of apparent wind and 6 knots of boat speed. That equals a TWA of 54*. So 30* apparent is not sailing that high.

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Old 27-04-2010, 18:24   #12
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Apparent wind is what the boat and sails see, much more useful than true wind.
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Old 27-04-2010, 19:16   #13
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DotDun said exactly what I was going to say. You sail by the apparent wind so that's what I'd set it for.
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Old 27-04-2010, 19:33   #14
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As Paul said you can go to the US sailing site and play with the program. Racing we sailed to a target speed. If you were supposed to be doing 7.3 upwind in 12 knots that is what you tried to sail. If you were faster then you were sailing fat, is slow then you were high.

Racing is racing and cruising is cruising, I wouldn't worry to much about it but if you want to know, contact the maker and ask for a polar and try to sail to it.

Cheers,

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Old 28-04-2010, 13:13   #15
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If you want to select "true wind", then you will have to feed the boat speed into the computer and you will be faced with another dilemma: speed through water (from speed log) or speed over ground (from GPS). There has been a heated discussion about this on the forum.

So, it's better to stick to "apparent wind".

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