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Can anyone give me an idea on fuel consumption of a 51' Symbol

Discussion in 'Symbol Yacht' started by jeff stauffer, Nov 12, 2017.

  1. jeff stauffer, Nov 12, 2017
    #1
    jeff stauffer

    jeff stauffer New Member

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    I am considering the purchase of a 51' Symbol with two Caterpillar 3208 engines. At say 7-8 kn/hr does anyone have an estimation of how many gallons of diesel I would use? If it is outrageous, I may have to consider another boat.
    Thanks.
  2. Capt Ralph, Nov 12, 2017
    #2
    Capt Ralph

    Capt Ralph Senior Member

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    Could you offer the engine tune? Natural, turbo, turbo & after cooled (TA) and final horse power?
    With that, you or us can find the fuel burn per rpm.
  3. Capt Fred, Nov 12, 2017
    #3
    Capt Fred

    Capt Fred Senior Member

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    The estimate can be fine tuned by the specifics but you should burn about 3 to 4 gallons per engine for a total of 6 to 8 gallons/ hour at 7 to 8 knots. After 8 knots the burn rate goes up significantly.
  4. jeff stauffer, Nov 12, 2017
    #4
    jeff stauffer

    jeff stauffer New Member

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    Thank you very much. Much appreciated. I went looking for HP of that engine and found out that there are many versions. From what you are saying, it's about a gallon per mile. Would there be any benefit to running one at a time. I believe that is a viable option on a Catamaran. It may be a dumb question but I am just throwing it out there. Thanks again for the help. Really appreciated.
  5. Capt Fred, Nov 12, 2017
    #5
    Capt Fred

    Capt Fred Senior Member

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    One to perhaps as high as 1.25 kt/gallon. The benefits of running on one engine is unique to each boat. I think generally it will be less efficient because there is such a crab angle created by the thrust misalignment and counter rudder. However you will save on engine hours and oil changes. Also need to consider if your transmission will allow for continuous free wheeling. That again is unique to the transmission some do and others do not. You will have to get the tranny model number and search if the tranny permits free wheeling.
  6. Capt J, Nov 12, 2017
    #6
    Capt J

    Capt J Senior Member

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    No and NO. Running on one engine on a yacht OR catamaran puts the engine in a VERY overloaded state (as the vessel is propped based on both engines) and you're going to burn more fuel for the speed because you're crabbing. If you're this cheap you shouldn't buy a yacht.
  7. Capt J, Nov 12, 2017
    #7
    Capt J

    Capt J Senior Member

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    AND lower your engine lifespan dramatically. The engine is in a very overloaded state running on one engine when it is propped based on 2 engines......the load level at each RPM point is about twice as high as the engines propeller curve.
  8. 30West, Nov 14, 2017
    #8
    30West

    30West Member

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    He mentioned 7-8kts, is he likely to be overloading his engine at hull speed, or just getting it into the bottom of efficient output?

    Most marine transmissions in that size boat are fine for freewheeling, some boats are moored in a channel with a current and they freewheel constantly. Still good to verify. If you are running dripless shaft seals, verify those are provided cooling water from both engines with a cross-tie between seals. Most seals have a second port to connect them to each other.

    It does seem like a catamaran will have more asymmetric thrust and more drag from rudders compensating, but that depends on how much the hulls tend to track straight and size of rudders and all that. Only way to know is try it out.