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| Can someone explain De-powering to me http://www.hobie.com/au/en/forums/viewtopic.php?f=13&t=9627 |
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| Author: | JSWoerner [ Wed Jun 04, 2008 5:39 pm ] |
| Post subject: | Can someone explain De-powering to me |
The more I read the less I understand. Why does de-powering make me faster? I grew up in the era of muscle cars and watched Tim "the toolman" Taylor exult "MORE POWER" Obviously when the wind and waves pick up I reef the jib and sail conservatively home but within the realm of safe sailing why do I want to de-power the sail. |
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| Author: | OlderBowman [ Wed Jun 04, 2008 6:37 pm ] |
| Post subject: | |
power in a sail is defined by its draft, the depth of the chamber of the sails. When the wind picks up to where the boat becomes hard to manage, you make adjustments to downhaul, mast rotation, outhaul... all to flatten the sail, making the draft less. This is depowering the sail. |
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| Author: | MUST5429 [ Wed Jun 04, 2008 7:01 pm ] |
| Post subject: | |
A full sail shape is like First gear in a car. Lots of power, not much speed. Used when the winds are light and/or when you are sailing "heavy" As you get overpowered, as evidenced by the inability to keep the hull from popping up out of the water, you start "shifting" into a higher gear by flattening the sail (depowering) and going for a "speed shape Think of the wing of an airplane. At takeoff, they extend the flaps for a full sail shape. Once they get up to cruising speed, they retract the flaps for speed, flat sail shape. A sail is nothing more or less than a verical wing. that is why pilots are usually such good sailors, they understand aerodynamics and sail shape. Not the best worded or complete explaination, but hopefully you get the drift. ( no pun intended) Stephen |
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| Author: | MUST5429 [ Wed Jun 04, 2008 7:45 pm ] |
| Post subject: | |
The only adjustment Older Bowman left out is Traveller. If you have downhauled, over rotated, outhauled, sheeted in hard, to the point of being over sheeted, and with those adjustments, gotten the sail shape as flat as you possibly can, the next step is to start bleeding the traveller out until you can keep the hull from popping up. You want to sail with the windward hull just kissing the top of the waves. When you allow the boat to heel more than that, the wind is spilling off the top of the sail, and you actually go slower. Altho, when not racing, knowing how to fly it high and in control is great fun. I call it "showboating for the tourists". Also, it is great fun to fly it high and make the girls squeel. Between the replys from Older Bowman and me, you got some information on both the how and the why, hopefully you got the information you were looking for. |
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| Author: | srm [ Thu Jun 05, 2008 5:34 am ] |
| Post subject: | |
An important mechanism to consider for depowering the sail is twist. This is controlled primarily by downhaul tension and mainsheet tension (the two controls that induce bend in the top of the mast). Twisting the upper portion of a sail relative to the apparant wind direction lowers the center of effort of the sail. This allows the sail to produce more power lower down. For a quick example, imagine a 10ft wide boat with a 300lb crew, and a 30ft tall rig. If the center of effort of the rig was located at the top of the mast (30ft), the maximum force the rig could produce sailing upwind would be 100lb. If the sail is twisted and the C.E. is lowered to say 10ft up from the base of the mast, the same rig & crew can now produce 300lb of force or 3 times the drive. (This is an extreme example, obviously the CE can't be located at the top of the mast). So in higher winds, be sure to pull a lot of tension on your downhaul to help flatten and twist the main. sm |
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