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Go Back   SailNet Community > General Interest > General Discussion (sailing related)
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  #21  
Old 07-04-2007
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The CCA boats have long overhangs. So as the boat approches hull speed it sinks further into the bow wave. As it does this, the overhangs are submerged, increasing the LWL even more.
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  #22  
Old 07-04-2007
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The CCA design was simply a 'ratings rule beater' and although the effective waterline (hull speed) did increase with boat speed, those large overhangs also produced a pronounced 'hobby-horse' motion when in waves ... which tend to slow down a boat.
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  #23  
Old 07-04-2007
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Giulietta is just really nice Giulietta is just really nice Giulietta is just really nice Giulietta is just really nice Giulietta is just really nice
but man...are they beautifull....
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  #24  
Old 07-04-2007
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The long ends of the CCA style of boat also adds buoyancy in the ends and flattens out the buttocks at the ends which helps to keep you from being pooped while running. Also another characteristic of the style is narrow beam with slack bilges and a curve of area that is more symmetrical forward and aft then modern boats. Makes for a gentle motion at sea and promotes easy steering. In fact a lot of CCA boats will self-steer while very few modern boats will do this for more then a few minuets at a time.
All the best,
Robert Gainer
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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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  #26  
Old 07-05-2007
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It has been my experience that hull speed is really just a useful guideline. I have been able to average higher than hull speed on some trips.
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Old 07-05-2007
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So with fresh water being lower density than salt water, boats will float lower in fresh water. This gives them more water line. Will hull speed be greater in fresh water than in salt water?
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Old 07-05-2007
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Not due to density but freshwater has a lower absolute viscosity (and lower surface tension) than seawater ... therefore faster in fresh water.
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Old 07-06-2007
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But if they sink further in the fresh water, they will have a lot more wetted surface and slow down.
pigslo
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Old 07-06-2007
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When you sail fast boats (like a CS) in salt water you have to be careful because the boat moves through the water so fast that the friction makes the water boil and vaporise leaving salt crystals on your hull that slow it down....
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