Diesel Fuel Consumption ?

Discussion in 'Sailboats' started by SCUBASailer, Nov 2, 2018.

  1. SCUBASailer
    Joined: Nov 2018
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    Location: Middletown, CA

    SCUBASailer New Member

    Likely there are those here that have either operated or chatted with those that have.
    I'm considering a Gulfstar 47 SM w/Perkins 135hp, and I'm curious what the fuel consumption is going to look like on a long passage at a conservative 5-6 knots.

    Just need a fairly close ballpark figure to see if I'm going to need to reduce the water storage and increase the fuel capacity.
  2. Barry
    Joined: Mar 2002
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    Barry Senior Member

  3. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    About 1.5 GPH.
  4. Barry
    Joined: Mar 2002
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    Barry Senior Member


    Attached is the Perkins fuel consumption table. The lower blue line is a representative prop that hits the 135hp rating of the engine at 2600 rpm. The upper line is the max hp you can get out of the engine at specific rpm
    1 Litre per hour = .26 US gallons per hour
    So depending upon the rpm that you are running, you can use up to 28 litres per hour, or 7 gallons per hour. Remember these are factory specs, new engine.

    So I would take the boat out for a spin, make a table of rpm vs speed. See if the prop maxes out at 2600 rpm, (so you know that this graph with this prop curve is representative) and you could come back to the graph, pick the speed that you want to know about, take this rpm and compare it to the table, convert Lph to USgph and it should get you close.
    This will then get you a fuel consumption of say 2 US gallons per hour, at 5 knots, so it would take .4 gallons to go 1 nautical mile at that speed, divide your fuel tank capacity by .4 and you will get your range. Allow a bit for reserve as it is unlikely that you would get every drop out of the tank, allow a bit more for the condition of the engine and you should be close.

    If you buy the boat, you should create your own graph, speed vs fuel usage or range as it obviously varies
    Last edited: Nov 4, 2018
  5. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    You can count on 2 gph or better, assuming it’s running well and fairly clean.
    Keep track of hours and gallons used and it won’t take long to refine your numbers.
    Top it off frequently for faster compilation of data.
  6. goodwilltoall
    Joined: Jul 2010
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    Location: nation of Ohio

    goodwilltoall Senior Member

    135 hp is a large engine, 1 gal. will do 15 to 20 hp which to get it down to doing 2 gph will vastly underload it
  7. Barry
    Joined: Mar 2002
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    Barry Senior Member

    fuel consumption formulas and tables https://barringtondieselclub.co.za/technical/fuel-consumption.html

    Attached is a site that tabulates fuel consumption per hour required for various horsepower values for naturally aspirated engines as well as turbo'd engines

    The value in this graph is that you can actually determine what the engine is producing in horsepower based on the fuel consumption used.

    Ie at 2 US gallons per hour, the engine is producing 35 horsepower

    at 4 usgph, the engine is producing about 70 horsepower

    Your max engine rated horsepower is 135 so therefore (theoretically) at max load of 135 hp at the corresponding rpm, your engine should burn about 7.5 gph

    Note though that most engines that give a specified rating such as 135 hp at 2600 rpm will normally use more at the max output conditions than what this graph might say because when the manufacturer prints the
    max hp rating, they are not concerned about fuel consumption at this max rating. Most engines when topped out have excess fuel available, EGT's can go through the roof, exhaust and inlet
    air velocities can be inefficient and incomplete combustion usually presents.

    Irrespective if these table values are 100 percent accurate, they are probably indicative of gallons per hour burned to horsepower produced

  8. SCUBASailer
    Joined: Nov 2018
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    Location: Middletown, CA

    SCUBASailer New Member

    Thank you ALL very much for sharing your wisdom and knowledge.
    Your responses give me a pretty good idea what to expect.
    Prop could be of course changed out to whatever is most efficient on the market at this time.
    If I understand this correctly, if I was to make a direct course (motoring) passage from Los Angeles to Catalina (~25 nm), and did so at a speed of
    5 knots, that would likely cost me about 10 gallons (20 gal round trip)... (?)
    Or am I all wet on that, and showing my ignorance...
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