I don't believe there is any measurable current in Chatfield Reservoir. It's a J-shaped inland flood control reservoir of about 2.33 square miles surface area and 27,000 acre-feet normal volume, on the South Platte River (also fed by the smaller Plum Creek). The U.S. Army Corps of Engineers generally controls outflow to first avoid downstream flooding, then keep the water level at 5,432' (full pool, ~75' max depth over riverbed) down to 5,423' in a drought. Right now there's 289 cfs flowing in and 120 cfs flowing out. It would be exceedingly rare for outflow to significantly exceed inflow, which would be the most probable way of causing any measurable surface-level current.
I know the RaceQs phone app reads out in knots. Available evidence indicates the website replays read out in knots as well, but I'm confirming with the company. I'm also trying to confirm the phone app's speed measurement algorithm. I assume it samples the phone's GPS position at some frequency, computes the distance between position samples, divides by the sampling period to yield speed, then does unit conversion to nautical miles per hour. Cheers, Randy ----- Original Message ----- From: "Gary Russell via CnC-List" <cnc-list@cnc-list.com> To: "C&C List" <cnc-list@cnc-list.com> Cc: "Gary Russell" <captnga...@gmail.com> Sent: Friday, May 19, 2017 12:00:40 PM 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 > 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 > 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 _______________________________________________ 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 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 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 All Contributions are greatly appreciated!
