All of this is based on a old (actually getting very old) coefficient that does not take into account that the waterline length is not static, the waterline length increases as the boat heal and gain speed. Moreover, as the prismatic coefficient is now better understood, recent boat designs with wide transom can easily go above the theoretical speed. My new boat (Alubat 36) can easily achieve speed in the 9-11 knots range under spinnaker. On my C&C 30, I consider my true hull speed to be 7,4 knots. I good winds, I will reach speed above 7 knots, but 7,4 seems to always be the limit for a sustained speed.
Antoine C&C 30 Cousin > Le 19 mai 2017 à 17:47, Bruce Whitmore via CnC-List <cnc-list@cnc-list.com> a > écrit : > > Hi all, > > Keep in mind that the hull speed is not the "maximum" speed that the boat > will acheive. It is the maximum speed at which the amount of energy needed > to cause the boat to go fast increases, and yes, it is a steep increase in > energy input from the sails. > > That said, our C&C 27 MKIII regularly sailed above the 6.4 kts. in > theoretical hull speed. That was measured by GPS, and of course, that > measures speed over ground which can be significantly affected by current. > That said, my sailing experiences on that boat were on Lake Michigan, in all > kinds of conditions. > > GPS sustained recorded hull speeds (meaning more than just a surf, but > lasting more than a minute at a time) would exceed 7.0 knots multiple times > in every season. Usually this required 12 - 15 knots of speed on an apparent > beam reach. > > On a couple transits between Chicago and Milwaukee, with apparent deep > reaches and sustained 15 - 20 kt winds, we had sustained 8.5 kt speeds, and > on one memorable night, we had sustained 10's, tracked by a friend's > permanently tracked GPS speeds (not just looking at the numbers). I'm not > sure I can dig up that log, but he might be able to find it. I'm not sure > I've heard of a current exceeding 2 kts on Lake Michigan, but others may know > better. > > And, no, even with heal, you might be increasing your waterline length by > 10%, but not much more, and considering the formula, that doesn't equate to a > 10% faster boat. > > So, its a guideline, not an absolute maximum. > > Hope you find this helpful (though you might find in unbelievable) > > Kindest Regards, > > Bruce Whitmore > > (847) 404-5092 (mobile) > bwhitm...@sbcglobal.net <mailto:bwhitm...@sbcglobal.net> > > > From: RANDY via CnC-List <cnc-list@cnc-list.com > <mailto:cnc-list@cnc-list.com>> > To: cnc-list <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com>> > Cc: RANDY <randy.staff...@comcast.net <mailto:randy.staff...@comcast.net>> > Sent: Friday, May 19, 2017 3:03 PM > Subject: Re: Stus-List Fun Race Last Night > > Ok that made me laugh :D > > That's why I first noticed that speed via the replay. I sure as hell am not > looking at my iPhone in the middle of that kind of chaos :) In fact this > past Wednesday night when I finally got a rail in the water, I even forgot to > look at my clinometer in all the excitement - but I suspect she was heeling > around 30 degrees. I know 25 degrees isn't enough to get the rail wet. > > Cheers, > Randy > > From: "Gary Nylander via CnC-List" <cnc-list@cnc-list.com > <mailto:cnc-list@cnc-list.com>> > To: "cnc-list" <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com>> > Cc: "Gary Nylander" <gnylan...@atlanticbb.net > <mailto:gnylan...@atlanticbb.net>> > Sent: Friday, May 19, 2017 12:11:53 PM > Subject: Re: Stus-List Fun Race Last Night > > I remember that Randy is on a lake in Colorado. More than likely his burst of > speed is the hull settling into the water as it goes faster and thus > increasing the waterline – and/or being heeled over which also increases the > waterline. When my 30-1 gets the rail in the water in 20-30 knots of wind, I > am generally too busy to look at the speed. > > I’m sure all of you nautical types remember the war stories about clipper > ships going so fast they literally bury themselves as the make a bigger and > bigger hole in the water. I am not interested in trying that. > > Oh well. > Gary > > From: CnC-List [mailto:cnc-list-boun...@cnc-list.com > <mailto:cnc-list-boun...@cnc-list.com>] On Behalf Of Gary Russell via CnC-List > Sent: Friday, May 19, 2017 2:01 PM > To: C&C List <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com>> > Cc: Gary Russell <captnga...@gmail.com <mailto:captnga...@gmail.com>> > Subject: Re: Stus-List Fun Race Last Night > > Remember your GPS gives you speed over ground, while Hull Speed is speed over > the water. A one knot favorable current can easily explain the difference. > > Gary > S/V Kaylarah > '90 C&C 37+ > East Greenwich, RI, USA > > ~~~~~~~_/)~~~~~~ > > On Fri, May 19, 2017 at 1:16 PM, Ronald B. Frerker via CnC-List > <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com>> wrote: > GPS is usually in miles per hour IIRC. Knots is faster by about 15%, so > 6.7kt times 1.15 would be about 7.7mph. > Unless your GPS is set in kt in which case this is all wrong. > Ron > Wild Cheri > C&C 30-1 > STL > > > > From: RANDY via CnC-List <cnc-list@cnc-list.com > <mailto:cnc-list@cnc-list.com>> > To: cnc-list <cnc-list@cnc-list.com <mailto:cnc-list@cnc-list.com>> > Cc: RANDY <randy.staff...@comcast.net <mailto:randy.staff...@comcast.net>> > Sent: Thursday, May 18, 2017 3:52 PM > Subject: Re: Stus-List Fun Race Last Night > > I'm just as surprised as anyone. I know that 1.34 times the square root of > 24.75 (Grenadine's waterline in feet) is 6.67 knots. But apparently that's > only a very general rule - see > http://www.boats.com/reviews/crunching-numbers-hull-speed-boat-length > <http://www.boats.com/reviews/crunching-numbers-hull-speed-boat-length/#.WR4GQccnuq0> > and https://en.wikipedia.org/wiki/Hull_speed > <https://en.wikipedia.org/wiki/Hull_speed>. At 9,000 pounds displacement I > guarantee I'm not planing :) > > But I assume GPS doesn't lie. On June 22nd last year I was using RaceQs > during a race. I forgot to switch it off after finishing, so it recorded > Grenadine sailing for fun in the 25-33mph gusts that piped up after the race, > under full main and 150% genoa (which tore that night, before I could get a > rail in the water). If you watch this replay from 19:42:50-19:43:00 local > time, you'll see Grenadine going 7.5 knots over ground according to RaceQs > GPS-based iPhone app: > http://raceqs.com/tv-beta/tv.htm#userId=1032518&divisionId=41508&updatedAt=2016-06-23T03:05:38Z&dt=2016-06-22T18:08:05-06:00..2016-06-22T21:05:54-06:00&boat=Grenadine > > <http://raceqs.com/tv-beta/tv.htm#userId=1032518&divisionId=41508&updatedAt=2016-06-23T03:05:38Z&dt=2016-06-22T18:08:05-06:00..2016-06-22T21:05:54-06:00&boat=Grenadine> > > I'm not one to look a gift horse in the mouth :) Maybe at 25 degrees of heel > my waterline length is appreciably longer than 24.75 feet. Or maybe I just > have to give credit to George Cassian, George Cuthbertson, and Rob Ball for > designing a faster-than-predicted hull form. > > Cheers, > Randy > > From: "David Knecht via CnC-List" <cnc-list@cnc-list.com > <mailto:cnc-list@cnc-list.com>> > To: "CnC CnC discussion list" <cnc-list@cnc-list.com > <mailto:cnc-list@cnc-list.com>> > Cc: "David Knecht" <davidakne...@gmail.com <mailto:davidakne...@gmail.com>> > Sent: Thursday, May 18, 2017 1:25:19 PM > Subject: Re: Stus-List Fun Race Last Night > > Theoretical hull speed of a C&C 30 is 6.7 knots (based on 25’ water line). > How are you hitting 7.6-8? Foils? Dave > > > > _______________________________________________ > > This list is supported by the generous donations of our members. If you wish > to make a contribution to offset our costs, please go to: > https://www.paypal.me/stumurray <https://www.paypal.me/stumurray> > > All Contributions are greatly appreciated! > > > _______________________________________________ > > This list is supported by the generous donations of our members. If you wish > to make a contribution to offset our costs, please go to: > https://www.paypal.me/stumurray <https://www.paypal.me/stumurray> > > All Contributions are greatly appreciated! > > _______________________________________________ > > This list is supported by the generous donations of our members. If you wish > to make a contribution to offset our costs, please go to: > https://www.paypal.me/stumurray <https://www.paypal.me/stumurray> > > All Contributions are greatly appreciated! > > > _______________________________________________ > > This list is supported by the generous donations of our members. 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