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.RonWild CheriC&C 30-1STL
From: RANDY via CnC-List <cnc-list@cnc-list.com>
To: cnc-list <cnc-list@cnc-list.com>
Cc: RANDY <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 and
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
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>
To: "CnC CnC discussion list" <cnc-list@cnc-list.com>
Cc: "David Knecht" <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
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