: thanks Matthew, that explained what they are supposed to do quite well.
: in practice, do they work?
: daren.......

Uuhhh. Well? I like `em......But I`m the last person one should ask about hydrodynamics (whatever happened to that George guy?) I would however, point out that most of the big companies (and my idol Joe Greenley) make them that way, so I suspect that shape must have some benefit.