To: "Donald C. Burdick" <burdickd@email.msn.com> Cc: trawler-world-list@samurai.com Subject: Re: TWL: Re: Hull Speed It is my understanding that it not a particularly accurate rule that one can multiply the sq root of the waterline length times 1.34 to find the max speed of a displacement hull. The actual max speed is a function of the hull design. (It will be approximately available by this calculation) Stated another way, the S/L is the sq root of the length times the maximum hull speed, but not a final determiner of actual hull speed of any given boat. (or at any speed for that matter). I suspect the only truly accurate way for a boat owner to arrive at maximum mileage is to use a fuel measuring device such as Flowscan and make accurate runs knowing current and bottom condition of the hull. Regarding my Nordic Tug, I have studied Cummins's fuel burn curves at given RPM which has Nordic Tug's speed rates overlaid (not very accurate) and have come close to finding efficient points of operation, but there are so many conditions that enter into how efficiently a given hull moves thru the water as to make any estimate with less than a 10% accuracy almost a single boat type of deal. Robert Murch Endeavor, Deer Harbor, WA Donald C. Burdick wrote: > >The bottom line is that every boat has a hull speed. > > ... Yet, I > believe our most fuel efficient speed is about 8.5 knots (1700 rpm's with > 24" diameter three blade 16" pitch propellers). This is slightly less than > the theoretical hull speed of 8.67 knots as calculated by the square root of > our waterline in feet times 1.34. > > But, others tell me the most efficient full displacement rate of travel is > only 70% of theoretical hull speed. For our vessel, that calculates to 6.07 > knots. > > Where do I find Grand Banks data, or from any other manufacturers of full > displacement or semi-displacement hulls, addressing fuel efficiency to > maximize cruising range? There must be some published chart curves out > there.