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  #21  
Old 07-23-2010
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When pulled in towards the centerline the barber hauler allows precision distance between the jib & main so that the correct aerodynamic 'dumping velocity' occurs at the exit of the 'slot' .... where the boats resultant speed and pointing ability (best VMG) is optimized. many ways to 'barber haul' ... multiple jib tracks and transverse tracks/travellers, etc.

As regards a 'happy bubble' ..... totally OK if the max boat velocity is attained as the 'bubble' is only a vectorial 'cancellation' of the aerodynamic circulation flow around both sails within the 'so called' slot, where the forward flow component of circulation on the windward side of the jib is greater than the aft direction flow over the lee of the main .... and the jib flow is predominating. The speedo (& VMG) is the validating instrument when the circulation flows are showing a 'happy bubble'.

Article that explains 'dumping velocity' for the layman: http://www.arvelgentry.com/techs/The...nteraction.pdf

Last edited by RichH; 07-23-2010 at 09:22 AM.
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  #22  
Old 12-05-2010
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Quote:
Originally Posted by Hartley18 View Post
Good post, Allene - and welcome to Sailnet.

..though I, for one, am not convinced that "the small bubble is fast" idea is the BEST anyone can do.

From what I've read and am seeing down-under, many crack racing yachts are going away from overlapping genoas (that cause the bubble in the fist place) back to almost self-tacking jibs - the theory being that, for anything other than really light winds, a smaller headsail will allow ALL the main to work - not just 90% of it - whilst getting a better rating.

Cheers,
I have been reading that a large genoa does not make the boat faster since it actually interferes with the pressure distribution on the lee side of the main. The majority of the power in a headsail or a mainsail is near the luff, since that is where the pressure is most negative. I have much more to read about that though.
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Old 12-05-2010
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Quote:
Originally Posted by RichH View Post
When pulled in towards the centerline the barber hauler allows precision distance between the jib & main so that the correct aerodynamic 'dumping velocity' occurs at the exit of the 'slot' .... where the boats resultant speed and pointing ability (best VMG) is optimized. many ways to 'barber haul' ... multiple jib tracks and transverse tracks/travellers, etc.

As regards a 'happy bubble' ..... totally OK if the max boat velocity is attained as the 'bubble' is only a vectorial 'cancellation' of the aerodynamic circulation flow around both sails within the 'so called' slot, where the forward flow component of circulation on the windward side of the jib is greater than the aft direction flow over the lee of the main .... and the jib flow is predominating. The speedo (& VMG) is the validating instrument when the circulation flows are showing a 'happy bubble'.

Article that explains 'dumping velocity' for the layman: http://www.arvelgentry.com/techs/The...nteraction.pdf
Excellent post!

Wow, dig the analog plotter in the photo of that article!

On my Star Class boat, the barber haul is a track athwartships that carries the jib block, with more modern Stars having another track perpendicular nearest the centerline of the boat for moving the first track fore and aft.
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Old 12-07-2010
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Quote:
Originally Posted by Starheart View Post
I have been reading that a large genoa does not make the boat faster since it actually interferes with the pressure distribution on the lee side of the main. The majority of the power in a headsail or a mainsail is near the luff, since that is where the pressure is most negative.
That may be true in theory, but in practice
an overlapping genoa is often faster.
There is a trend towards non-overlapping headsails,
partially driven by IRC ,in the latest generation
of Gran Prix boats. But even these boats will use
a Code Zero or Mashead genoa upwind in light air.
You may also note that the BMW Oracle tri, likely
the most refined sailing craft ever, often
used headsails with quite a bit of overlap.
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Old 12-07-2010
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Quote:
Originally Posted by COOL View Post
That may be true in theory, but in practice
an overlapping genoa is often faster.
There is a trend towards non-overlapping headsails,
partially driven by IRC ,in the latest generation
of Gran Prix boats. But even these boats will use
a Code Zero or Mashead genoa upwind in light air.
You may also note that the BMW Oracle tri, likely
the most refined sailing craft ever, often
used headsails with quite a bit of overlap.
Yeah, I'm still reading a lot about this stuff, mostly Arvel Gentry's articles. I don't know where I got the idea that a genoa is not faster than a normal jib.
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Old 12-07-2010
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What you may have heard and been thinking is that a large genoa is less efficient (meaning more heeling and drag for the same amount of drive), but in lighter air or deeper sailing angles it may be faster.

The way that modern race boats are designed, they start out with a comparatively large and efficient standing sail plan relative to their drag and so rarely need more sail area beating or even close reaching even in light air, but they generally fly large reaching sails as soon as they are broad off the wind.

Jeff
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  #27  
Old 12-07-2010
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Quote:
Originally Posted by Jeff_H View Post
What you may have heard and been thinking is that a large genoa is less efficient (meaning more heeling and drag for the same amount of drive), but in lighter air or deeper sailing angles it may be faster.

The way that modern race boats are designed, they start out with a comparatively large and efficient standing sail plan relative to their drag and so rarely need more sail area beating or even close reaching even in light air, but they generally fly large reaching sails as soon as they are broad off the wind.

Jeff
I guess the drive from something like an asymmetrical spinnaker is greater than the drag also otherwise they wouldn't use them.
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