OK, thanks all again who participated... in my questions on the other thread.
now if you read through the other post you can get an idea of what apparent wind is... it is what the sail (or your face) feels as the wind.. and you need to sail to that.
it is my understanding and method:
the way to build your apparent wind is to go faster.. the faster you go.. the more you move the wind direction
an example is: riding a bike with a breeze that is blowing in your ear to start .. will move to your cheek and eventually straight your nose when you hit enough speed (similar to the car example)...
but this doesn't mean much if you dont know how to maximize apparent wind.. and the physics also dont mean much if it isn't utilized.
now i am no expert, and as i said.. as of last year.. i had no clue. it wasn't until i was sailing with a 74 year old and he told me when i had it and when i lost it.
I had heard of it, and had the concept down.. but couldn't recognize when i was taking advantage of it, or when i lost it...
SO ... what i do.. is build my speed up to move the apparent wind (or move it forward) and then i fall off.. and slowly point up.. and repeat. this is much more obvious (or APPARENT) downwind... as you point higher.. you go faster.. then fall off.. and enjoy the speed... and repeat..if done correctly.. you can keep that going until you are going faster than the actual wind...
here are 2 links.. 1 is for kids and makes sense,. the other is for rocket scientists.. and puts me into a coma...
http://boatsafe.com/kids/bramp1099.htm
http://londonarea.ms-sc.o…rt2/sail/BasicTheory.doc
please edit or add your own thoughts / corrections...
edited by: andrewscott, Sep 24, 2009 - 04:51 PM
how to maximize apparent wind....
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Posted: Sep 24, 2009 - 04:29 PM
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Posted: Sep 24, 2009 - 11:42 PM
OK so here's the part I've not been able to get. And it is described the same way you describe it in other references.
When running you point towards the wind (say 20 degrees off of downwind or so) to build up speed therefore increasing the apparent wind. Then you bear further downwind a bit (say to 15 degrees off downwind). Wash and repeat.
So are you constantly changing course to go a bit upwind and then bearing downwind as your speed comes up? What does that accomplish? Why wouldn't you just point a bit upwind and leave it there for a while, then jibe to the same point on the other side?
I know I'm missing something here, if you can figure out what I would be greatly appreciative. My downwind sailing has sucked so far.
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Dave Bonin
1981 Nacra 5.2 "Lucile"
1986 Nacra 5.7 "Belle"
Winnipeg, Manitoba, Canada
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Posted: Sep 25, 2009 - 03:20 AM
the process of continually changing course a little, to build speed, and then using that speed to nip a little closer to your destination is well described in "catamaran racing for the 90's"
think of it as riding a bicycle and finding you balance by moving a little left and then a little right
without this little balancing act on the rudders you end up with less than ideal vmg -
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Posted: Sep 25, 2009 - 09:22 AM
by moving off the wind a little and then back up a little.. you increase the speed (faster than the actual wind speed)...in the long run you will make up the extra distance traveled by realizing a faster speed that in the long run will get you there faster than if you just go straight i.e. VMG (velocity made good) -
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Posted: Sep 25, 2009 - 09:24 AM
From the Hobie forums:
In his book, Catamaran Sailing from Start to Finish Phil Berman has this to say (in his intermediate sailing section)
Quote:
DOWNWIND SAIL TRIM
With an understanding of how tell-tales work, you can keep your sails working at their optimum, especially when you?re tacking downwind. The course that gives the most speed for the least extra distance is about 135 degrees from the wind, or about 90 degrees from the apparent wind (figure 6).
When your shroud yarns are streaming directly across your cat, you?ve got a 90-degree apparent wind. If you sail higher than 90 degrees (to 70 or 80 degrees) the shroud yarns will angle forward of the beam. And if you sail too low (100 to 110 degrees off the wind) the shroud yarns will angle behind the beam. So, to keep the wind at 90 degrees, watching the shroud yarns is critical. You want to sail as low on the wind as you can without cutting off the flow of air across the backside of your sail(s). A good way to get at this trim is to start the run with your sail(s), traveler(s) and/or barber hauler all the way out. From this point, slowly trim the sail(s) in and head up .until the leeward tell-tale begins to lift and flow aft. If the shroud yarns don?t indicate a 90-degree apparent wind, you have to either alter your course or sail trim until they do. Remember, you can?t get a 90-degree apparent wind if your sails are not receiving air flow across their Leeward sides.
Reaching downwind in a series of tacks is something most catamarans do with no problem. However, una-rigged cats with Less than 130 square feet of sail area cannot sail effectively by tacking downqwind with the wind at 90 degrees. Small unarigs just can?t generate enough speed with the wind at 90 degrees to justify the extra distance sailed.
I am interested in your take on this.
That's it for going downwind fast, especially on a H18 (or Alfred's H16). DON'T LOSE FLOW ON THE LEE SIDE OF THE SAIL! You lose flow and Bob Curry says you lose five boat lengths getting flow re-established!
How do you see flow on the back side? Use the black beauty tell tales, and put one 4 to 6 inches above or below the opposite one, this will help you see the lee tale "through" a colored sail panel. Still can't see the lee tales? Have your crew call flow on the back side. Keeping the boat at 90 degrees (apparent wind) gets easier with practice. You'll develop a feel for it and will be able to feel the boat slow and head up to KEEP FLOW, and head down in the puffs, sailing an 'S' pattern. Time on tiller... Oh, and gybe back into those puffs.
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In my last few sails, I have found I am much more able to maintain the flow on both sides and keep the apparent wind direction 90 degrees. Unfortunately, its more intuitive than something I can explain how to do. I just keep tinkering with course and sheeting in until things are optimal.
Thank you for continuing this discussion. To utilize a stop light, you don't need to understand electricity or light theory, you just have to know what to do based on the information you have (red or green). The same is true of apparent wind, except you have control over what you see. With experimentation, you will find the right combination so you "see green instead of red."
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