LDL hull vs 70kts rib

Discussion in 'Boat Design' started by veradotrips, Apr 15, 2015.

  1. veradotrips
    Joined: Apr 2015
    Posts: 1
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    Location: Sweden

    veradotrips New Member

    Hello this is my first post here. I am a big fan of the whole ldl concept both for smaller boats eg Nigel Erens and larger boats like the Steves FPB series.

    But i looked at Nigel evens site where he specifies the fuel consumption of the Range Boat 39 which according to him would be 1,2 L/NM at 14 knots.

    Range Boat 39 fuel consumption:
    http://www.nigelirens.com/boats/power-boats/rangeboat


    Does this not seem kind of high? 1,2 L/NM is very close to the fuel consumption of the Goldfish 38 Supersport, which is a 38 ft rib with twin 370 hp Mercury diesels which pretty much breaks the sound barrier compared to the range boat, with a top speed of 68 knots. At 40 knots this boat consumes just 1,4 L/NM. and with the smaller 300 hp Mercury diesels it comes down to 1,2 L/NM.

    Goldfish 38 supersport fuel consumption:
    http://build.goldfishboat.com/drivetrains/model/4/drivetrain/3/

    Goldfish 38 supersport:
    http://www.goldfishboat.com/individuals/buy/boats/38-supersport/

    The Goldfish is a notorious treehugger high speed powerboat but it should not be this close, right? Have i misunderstood something here?
     
  2. Rurudyne
    Joined: Mar 2014
    Posts: 1,162
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    Location: North Texas

    Rurudyne Senior Member

    I'm guessing the 3000 lb displacement difference has a lot to do with it. One thing I'm sure about, as you'll be aware, with the LDL boat backing off the throttle a couple kts will really drop the power, maybe half or maybe less. So that may be something like 70% better economy at 12 kt? Does that sound about right?

    The Rangeboat isn't an unusually narrow boat, not even 4:1 LBR, not like a Bolger Wyoming that displaces about the same but is 50' x 8', so while it is benefitting from the low displacement/length aspect it is not picking up economy, or giving up elbow room, from/to a high length to beam ratio that might enable it to sip less fuel still.

    ... and it's a whole lot prettier.
     
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