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Additional diesel fuel tank |
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While diesel is used in the main engine to turn the propeller and provide propulsion, there is no standard “miles per gallon” type of measurement as is used in cars. Actually, mileage is so bad in sailboats compared to cars that the ratio is better expressed as “gallons per mile”, fuel efficiency only happens with very large cargo vessels - while these can burn tons of fuel per hour, their sheer size gives them an incredible efficiency in terms of fuel used per ton of cargo carried per mile. I remember paying more for trucking items 200Km to the port than for transporting them to the Caribbean!
Unlike in cars where road conditions generally remain the same over long stretches and thus a measure of “Miles/Gallon” is meaningful, in a boat the sea and wind conditions plus sail use play a major factor in determining what speed the boat travels for a given engine RPM. Thus in boating one uses Gallons/Hour (or Litres/Hour) for a given engine RPM and then one can figure out the mileage for the actual conditions at sea. The main fuel tank on Zanshin holds 420 litres of diesel, which is a pretty good amount for a production boat, but at a consumption of 4 litres per hour this would only allow for approximately 105 hours of motoring (4 days).
With the conversion of one water tank with a capacity of 310 litres to diesel and installation of a fuel transfer pump the total fuel capacity goes up to 730 litres, or 182 hour (7.5 days) of motoring at 4 litres per hour. I am not quite sure of the exact values, but I believe 4 litres per hour is about 2000 RPM and that gives me a good 6-8 knots in calm conditions. Usually when running under engine one is trying to get out of the way of inclement weather and if I use 6 knots to account for waves, then an optimistic range would be 6 * 182 = 1092 nautical miles. While I don't plan on using this range, it is nice to have sufficient fuel for motoring when necessary plus reserves for using the generator as much as one would like.
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