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Old 07-04-2007
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There is more than one LWL for each boat.
Some manufacturers even publish "static" and "dynamic" LWL.
When you are sitting flat in the water you can probably see that the stern is not touching the watter - there is some overhang. When you move (motor for example to eliminate heel from experiment) you can notice, than the faster you go the deeper the stern sinks and higher the water rises - extending the water length. Add heel and it is a bit longer again. Also the formula is not accurate for all boats. The narrow stern boats should use a bit smaller factor as the narrow stern can not support the weight of the boat even before the wave is at the end of the boat, so the stern sinks.
The boats with relative wide sterns can use larger factor because even when the wave is almost at the end of the stern it can still support the weight of the boat.
The factor is some sort of average for traditional design boats.

Of course very light boats with large sail plan are powerful enough to climb over their bow wave and start planning (most hi.perf. racers like America cup boats or Giu's boats), but than that is no longer displacement sailing.
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Beneteau Oceanis 473

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