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.

Second fuel tank The black rotomolded tank for an additional 310 liters of diesel replaces a blue water tank of the same size in the same location. Since I've got a watermaker I don't need all that extra water and prefer to have diesel aboard.
(2014-02-08 16:50:31 NIKON D7100 with a "18.0-250.0 mm f/3.5-6.3" lens. [f/3.5, 1/25s] ISO 100)
Second fuel tank
Rotomolded second fuel Tank This black tank replaces an identically sized blue water tank on Zanshin in order to boost the diesel capacity by 310 liters.
(2014-02-08 16:49:57 NIKON D7100 with a "18.0-250.0 mm f/3.5-6.3" lens. [f/3.8, 1/60s] ISO 100)
Rotomolded second fuel Tank
Fuel transfer running The transfer of fuel from the 1/4 full second fuel tank to the 3/4 full primary fuel tank is running. If the valve is not closed, the fuel will slowly trickle back to the secondary tank over time.
(2014-02-08 16:49:41 NIKON D7100 with a "18.0-250.0 mm f/3.5-6.3" lens. [f/4.2, 1/60s] ISO 100)
Fuel transfer running
Fuel transfer process finished The STOP means that the sensor shows that the main tank is full and the transfer process has been stopped.
(2014-02-08 16:51:15 NIKON D7100 with a "18.0-250.0 mm f/3.5-6.3" lens. [f/5.3, 1/60s] ISO 100)
Fuel transfer process finished
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