Martin, "end plate effect" is what I was thinking about. The deck is the end plate for a sweeper.
Joel On Wed, May 7, 2014 at 1:32 PM, Martin DeYoung via CnC-List < cnc-list@cnc-list.com> wrote: > Calypso's headsails were also cut for a furler with the higher foot, now > about 18" off the deck. > > We still get a significant "speed bubble" in the main at the mid to upper > wind range for the light and heavy #1s. The bubble shows up 6' to 25' (off > the deck) on the mainsail. > > From my miss-spent youth crewing with serious race programs I expect there > to be an advantage to the deck sweeper type headsails, more so for the > early IOR type sail plans with big fore triangles and smaller mainsails. > The engineers may reference something about an end plate effect. > > Over the last 10 years of club racing Calypso with roller furling > headsails we see a significant decrease in performance at the low end of > the wind range, especially in acceleration. Side by side with another C&C > 43 that had newer, non-furling headsails Calypso was left in the dust as > the wind built from calm to 5 knots. Once the TWS was above 7 knots the > speed difference was much less but the newer sails still pointed higher. > > After reading about your +6 per mile for the roller furler I need to take > a close look at the PHRF-NW book and re-file Calypso's data. We are still > using the old IMS/IOR type measurements. > > Martin > Calypso > 1971 C&C 43 > Seattle > > -----Original Message----- > From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Dennis > C. via CnC-List > Sent: Wednesday, May 07, 2014 5:51 AM > To: cnc-list@cnc-list.com > Subject: Stus-List Technical sail discussion > > I recently re-filed my PHRF certificate to get +6 seconds for a roller > furler. Subsequently, I just had the luff my Mylar/Kevlar 155 cut down to > fit on the furler. My sail maker cut a bunch off the foot. > > I was chatting about losing the sail area with one of the really good > sailors in the club. He said it may actually be a good thing that the foot > is higher off the deck. He said with the older narrow IOR designs, deck > sweeper genoas may cause the slot to be less efficient. Might increase the > bubble in the main. > > In my simplistic mind I kinda see where he's coming from. The slot gets > restricted at the deck by the cabin. The lower part of the air flow would > get pushed upward into the bottom of the main. A higher foot allows some > flow to escape and keep the air flow lines smooth in the lower slot. > > Does this make sense? > > Dennis C. > Touché 35-1 #83 > MandevilleLA > > Sent from my iPhone > _______________________________________________ > This List is provided by the C&C Photo Album http://www.cncphotoalbum.com > CnC-List@cnc-list.com > _______________________________________________ > This List is provided by the C&C Photo Album > http://www.cncphotoalbum.com > CnC-List@cnc-list.com > -- Joel 301 541 8551
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