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Old 02-18-2010, 11:23 PM
Gary Baigent Gary Baigent is offline
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Join Date: Jul 2005
Rep: 485 Posts: 2,431
Location: auckland nz
Someone said they were dumping ballast from the LEEWARD hull at one stage in the second race on the reaching legs - perhaps to gain more buoyancy and lift that fairly well immersed hull up to reduce drag, maybe. Or maybe to lighten the boat so the windward hull flew more steadily, without dumping. This may just be gossip. In the first race they dumped a huge quantity from the windward one when doing the downwind leg, when the wind lightened - and from then on A5 held the gap between BMW-O steady. The real difference between the two boats was that BMW-O could crank far more power into their wing main and although A5's looked better than the flat board used in race 1, it was still very flat - and that would not have helped their hull balancing tight rope act either. It would be fascinating to see a compiled research of the two boats logs? in a book - if ever they allow that information to be released. It would be a good seller to those who want to be enlightened - and who are just guessing and surmising at the moment.
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Old 02-19-2010, 05:01 AM
booster booster is offline
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Join Date: Apr 2009
Rep: 24 Posts: 188
Location: Sweden
Note that the massinertia is proportional to the square of the lever arm (times the mass). Any pitch (roll or yaw) thus is strongly depending of the hull geometry and where the ballast tanks are located. Increasing the massinertia lowers the frequency of the system (and increases the its period). Alinghi seemed to have lower pith frequency than BMW Oracle, indicating more distributed mass, and longer lever arms. Regarding free surfaces anti-sloshing material has been used for long time in the automotive industry. When the hula-NZ lost the Cup some of the challangers simply used the sailbags as kind of anti-slosh devices.
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