Fuel Consumption Question Silverton 31

Discussion in 'Powerboats' started by derf, May 12, 2008.

  1. derf
    Joined: May 2008
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    derf New Member

    I am consider purchasing a 1986 Silverton 31 Convertible aproximately 12000 lbs powered by twin vortec EFI 325 Hp and Bravo outdrives. Does anyone have a rough idea of fuel consumtion when operating on plane and when in displacement mode. Any rough guesses from similar boats will help. Thanks
     
  2. charmc
    Joined: Jan 2007
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    charmc Senior Member

    Not exactly equal, but this is from a recent test of a newer Silverton 33' flying bridge convertible similar to yours. The boat is 16,000 lbs and engines are a bit more powerful than yours. A good guesstimate would have your boat getting 20-25% better mileage.

    RPM MPH/KTS GPH MPG/NMPG SM RANGE NM RANGE Db TRIMĀ°
    1000 5.8/5.0 1.8 3.19/2.78 575 500 66 0.5
    1500 7.9/6.8 3.0 2.62/2.28 471 410 73 0.5
    2000 10.9/9.4 6.2 1.75/1.52 315 274 77 2.0
    2500 12.4/10.7 11.8 1.05/0.91 188 164 82 4.5
    3000 13.4/11.7 19.2 0.70/0.61 126 109 83 7.0
    3500 19.4/16.6 27.8 0.69/0.60 124 108 85 10.0
    4000 23.2/20.2 36.2 0.64/0.56 115 100 85 7.0
    4500 31.1/27.0 44.2 0.70/0.61 127 110 91 6.0
    5000 33.4/29.0 48.2 0.69/0.60 125 108 92 5.0
    5400 35.6/31.0 50.8 0.70/0.61 126 119 92 4.0
     
  3. RockLaker

    RockLaker Previous Member

    Again, not the same boat but could help compare, my uncle had a 1990 34' Silverton Express Cruiser with twin 454s. Back in the day when it was new he said at WOT it got 1 mpg per engine. I know that's not proper fuel talk for boats, but the boat did about 40-43 knots at WOT. By the way, that's going by 4.54 litres in an imperial gallon.




    RL.
     
  4. Mik the stick
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    Mik the stick Senior Member

    DERF
    I know more about aircraft than boats but engines are engines. petrol engines use about 0.48lbs per hour per horsepower and diesels about 0.26lbs. If your boat is a 325hp petrol job and it does 43 knots flat out, it might cruise at 36 knots on 240hp. If this were a fact you would use 325 x 0.48 = 156lbs of petrol. 152/7.2lbs per imp Gall means you get 43knots (distance) in an hour using max power and 21.1 galls of fuel. In the cruise you would get 36knots and use only 16 imp galls.
     
  5. jonr
    Joined: Sep 2008
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    jonr Senior Member

    > 0.48lbs per hour per horsepower and diesels about 0.26lbs

    Perhaps a typo - .48 and .36 are more typical.
     
  6. Wavewacker
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    Wavewacker Senior Member


    I'm scratching my head here, what aircraft burns diesel? Avgas I know, JP4 I know but diesel?

    But I do know there is no compairson between aircraft and a boat even if they had the same engine, a tail wind only helps if the sails are full and I've not seen a plane in 6' seas or calm waters....LOL :D
     
  7. CDK
    Joined: Aug 2007
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    CDK retired engineer

    Derf wrote his only post on 5-13-2008 and never looked back....
     

  8. Mik the stick
    Joined: Dec 2012
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    Mik the stick Senior Member

    Typo? Yes, I have worked out the Specific Fuel Consumption of some WW2 submarines to be about .4 lbs/hp/hr. it very much depends on the engine and its condition.
    Trust me there are a few diesel engines available for light aircraft.
    SFC is the pounds of fuel used each hour to produce the required horsepower, driving a car on the road, a boat in the water, an aircraft in the sky, it makes no difference. in a steam powered ship that fuel might be wood, coal, or heavy oil.
    mik the stick
     
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