aparent wind pop quiz

[extremely_ed]

Hello everyone<br /><br />I am a high school student. This is my 2nd day of school my teacher says "ok, in 2 days you will get a quiz on aparent wind and how it makes sail boats beable to travel faster then wind".<br />She says to obtain tops marks we must beable to explain it with diagrams also.<br />Soo I've done searching around and havent found anything that will help me.<br />Can any of you?<br />It would be greatly appreciated.<br />Thanks<br />Ed

 

[sloopy]

Re: aparent wind pop quiz

HI edd!!!! I am also in High school, and sail, the topic o apearent wind is to much to talk about, go to sailnet.com and go to the learn to sail section and use there search feature, you might also want to know that the keel and center of effort is what makes the boat go faser then wind, you also got to facter in the water line length, and sail area, but sailnet should help you get the basic answers. apparent wind is also the wind relevent to the movement of the boat so do a sailnet search and check with your teacher

 

[naughtybynature]

Re: aparent wind pop quiz

in a nutshell... apparent wind is the movement of air across the airfoil (sail) created by movement of the boat. the movement is caused be the actaul wind, then as the boat reaches true windspeed, the airfoil will start to realize the benefit of apparent wind. most sialboats will never really reach this point as hull speed will handicap them, but windsurfers and iceboats thrive on this theory. have you seen a windsurfer do 40 knots in 25 knots of wind? this is because the windsurfer is creating its own wind after true max windspeed thus creating more lift and further wind speed across the sail as the board moves faster and faster across the water. get? got it? good.

 

[Knoxes]

Re: aparent wind pop quiz

Well, if I can add one more thing, here's how it feels. You're walking in a straight line at a slow pace, the wind is blowing directly from left to right. You can feel the wind on your left side. If you begin to run, you feel the wind on your face, as tho it had shifted and is now blowing from in front to back of you, when in fact it hasn't shifted, but since you are now moving quickly, thru the air, you have "created" wind in addition to that which is still blowing from left to right. That's what it feels like. Similar to the idea that if you stick your head out the window of a moving car, the wind isn't moving at 65mph, you are. If it were blowing in your same direction at the same speed, you wouldn't feel it, right? For a more detailed explanation, take Sloopy's suggestion, and go to sailnet.com.

 

[SCO]

Re: aparent wind pop quiz

Caution, to conclude that apparent wind creates more lift which in turn creates more speed...is a common misconception on par with the theory of perpetual motion. The apparent wind is the vector sum of the negative boat velocity and the true wind velocity. On a beam reach, with true wind coming perpendicular to the boat, the only thing pushing the boat fwd is the true wind component of the apparent wind. The boat speed component of the apparent wind is pure drag. Trust me on this, I know what I'm talking about. What an ice boat sees is wind coming from almost straight fwd, but the key is almost. As the boat accelerates to top speed from a stop, with true wind from the beam, the apparent wind clocks fwd until equilibrium is reached. That equilibrium apparent wind is farthest fwd with the iceboat.

 

[extremely_ed]

Re: aparent wind pop quiz

Hello and thanks everyone alot for the quick replies. The little quiz will probobly take place tommorw, so i want to get this all straight.<br />Ok from what she said, all we have to do it write a discription on how apparent wind makes the sail boat capable of going faster then the wind. with a diagram. So I have a diagram now.. but im not sure how to really say it.. because ive read soo many articals about it... <br /><br />Well i have a diagram, but do not know how to send it here but I have it saved from paint <br /><br />Could someone tell me how to word it soo it is true and im not confusing myself writeing untrue things.<br /> thanks again to you who have helped!<br />Ed

 

[Knoxes]

Re: aparent wind pop quiz

Well, I kinda hesistate to do this, because I don't want to give the answers away . That's why I posted on how it feels, so you can get an understanding of how it works - I'm sure thats the point of her lesson. So, simply put, it's a combination of the true wind, and the boat speed wind (combo depending on other variables), which, combined, is more than the true wind, so with more wind, more speed (in theory), so the boat can actually surpass the true wind speed.

 

[SCO]

Re: aparent wind pop quiz

Ed, my problem is that people conclude that the increase in apparent wind speed is the cause of the boat going faster and faster. It is an effect, not a cause. Were I you, I would understand it and present it correctly. Ill give you the 2 answers, first what the teacher seems to believe from the phrasing of the question ..that the apparent wind causes the boat to go faster, and 2nd the real thing. <br /><br />1) teachers version <br />As the boat starts from a stop with wind from a beam, the boat accelerates and the speed of the boat vectorally combines with the true wind speed to create an apparent wind of greater magnitude than the true wind speed. This greater apparent wind, the wind that the boat experiences, in turn propels the boat to a greater speed resulting in an even greater apparent wind speed. This process continues until the drag on the boat can no longer be overcome by the force on the sail. <br /><br />2) the real thang:<br />As the boat starts from a stop with wind from a beam, the boat accelerates and the speed of the boat vectorally combines with the true wind speed to create an apparent wind of greater magnitude than the true wind speed. Many think that this increase in apparent wind is the cause for the boat to continue accelerating to a speed greater than the the wind velocity. I submit that the increase of the apparent wind is an effect, not a cause of the acceleration. The argument that a boat creates its own wind seems to imply a manufacture of energy to accelerate the boat from nothing. All speed and acceleration of the boat is gained by changing the direction of the true wind with the sail. In the case of the beam reach, the true wind approaches the boat path at right angles, regardless of the speed of the boat, so the speed of the boat can be increased infinitely theoretically in the case of no drag acting on the boat from wind or water and some kind of perfect sail. In the real world there is drag and imperfection. As the boat accelerates, the apparent wind increases and moves forward. The forward( vs beam) component of the apparent wind increases drag on the boat. To adjust for the increased speed the sail is sheeted in to allow for continued turning of the true wind and extraction of force for acceleration of the boat. The acceleration continues until forward force derived from turning the true wind is equal to the rearward drag from water and wind.

 

[SCO]

Re: aparent wind pop quiz

Ed , if you are still out there, tell us what you did and what happened. Also , I have no intent to be critical of anyone here, especially the teacher. This just happens to be a pet issue with me, and I thought a good opportunity to explore the concept. I am surprized no one else posted back