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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
FW: Barrels was DR thread from Nov-Dec '04
From: Doug Royer
Date: 2005 Feb 1, 10:42 -0800
From: Doug Royer
Date: 2005 Feb 1, 10:42 -0800
Doug George posted a plausible explanation of the cube method, but I have not seen your posting on how a merchant marine would solve the problem. Any hope I will see another way to skin the cat from you? Bill Here you go: s = old speed S = new speed c = old consumption C = new consuption w = pld displacement W = new displacement r = rpm at s R = rpm at S Ve = calculated speed by rpm Vo = observed speed De = calculated distance by rpm Do = observed distance Slip - slip = vessel speed outruns screw speed + slip = screw speed outruns vessel speed by speed % slip = ((Ve - Vo)/Ve) x 100 by distance % slip = ((Do - De)/De) x 100 Fuel Consumption by displacement log C = (log c + 2/3 log W)- 2/3 log c by speed C =(c x S cubed)/s cubed Speed by RPM speed in Kts = (60 x rpm x pitch x (1 - % slip))/6080 rpm at given speed rpm = 6080/((pitch/1 + % slip) x 60) x speed in Kts rpm needed for new speed rpm = (r x S)/s