Running single on a twin to save fuel

Discussion in 'Diesel Engines' started by Easy Rider, Oct 23, 2010.

  1. Icebreaker
    Joined: Feb 2011
    Posts: 10
    Likes: 1, Points: 0, Legacy Rep: 11
    Location: Thailand

    Icebreaker Junior Member

    Here we go

    Displacement hull 66 tons
    Gross loaded tons 65
    Net tons 33
    Hull Speed 9.4

    2 Volvo 225 HP diesel engines Model TMD100Ak
    1 Gear Box SCG MF16-11c
    1 Saffle adjustable Pitch Prop

    Running both engines in calm seas with SOG of 8 knots uses 60 litres/hour

    How many litres/hour with 1 engine ?? at say 7 kts in calm seas ??????
     
  2. powerabout
    Joined: Nov 2007
    Posts: 2,913
    Likes: 62, Points: 48, Legacy Rep: 719
    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    I have done a few tests on displacement megayachts 40 to 50
    metre and they all used way less fuel on one engine at less than full speed
    I guess it depends on the power to move the hull versus the gph with the 3412 or 3508's running with very little load before they start to get much boost.
    The problem is you can overload a single engine if you nail it and usually the gearbox is not designed to windmill unless supplied with prop side oil pump.
    Was handy to know at what rpm you went to overload just in case you did need to run hard on one engine
    Was also interesting to know that it was always at a different rpm ( by a few hundred) on each engine due to one gearbox going the other way.
     
  3. Icebreaker
    Joined: Feb 2011
    Posts: 10
    Likes: 1, Points: 0, Legacy Rep: 11
    Location: Thailand

    Icebreaker Junior Member

    To Clarify:
    The vessel has only ONE Gearbox, One Propeller

    "
    The Vessel
    62.5 ft LOA
    49ft LWL
    Displacement hull 66 tons
    Gross loaded tons 65
    Net tons 33
    Hull Speed 9.4

    2 Volvo 225 HP diesel engines Model TMD100Ak
    1 Gear Box SCG MF16-11c
    1 Saffle adjustable Pitch Prop

    Running both engines in calm seas with SOG of 8 knots uses 60 litres/hour
    The Question :-
    How many litres/hour with 1 engine ?? at say 7 kts in calm seas ????
    "
     
  4. FAST FRED
    Joined: Oct 2002
    Posts: 4,519
    Likes: 109, Points: 63, Legacy Rep: 1009
    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    How many litres/hour with 1 engine ?? at say 7 kts in calm seas ????

    If your displacement is correct at 66long tons , and the number is not the registered tonnage , which is volume not displacement .

    2HP per ton , perhaps 2.5 should do the job, so the question becomes how efficiently does the single engine create 150-160HP ?

    The simplest solution , that IS worth the bucks is to install a Flow Scan that hooks to both engines and the GPS.

    This will give instant reading of MPG. www.floscan.com/

    FF
     
    1 person likes this.

  5. powerabout
    Joined: Nov 2007
    Posts: 2,913
    Likes: 62, Points: 48, Legacy Rep: 719
    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    f you have the fuel flow you just need to spec sheets of the engine to work out how much load they are under at that speed.
    If the BSFC goes down at a higher rev then you would be better off with one engine thats an easy one.
    To work out anything else you would need the load curve ( some call that the prop curve) of the vessel
     
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