Contra-rotating surface drives

Discussion in 'Surface Drives' started by Martin Tilbrook, Oct 30, 2006.

  1. yipster
    Joined: Oct 2002
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    yipster designer

    [​IMG]
    here a pic of apearantly normal DPX volvo surface props
    amazing your faster on regulars
     
  2. longliner45
    Joined: Dec 2005
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    longliner45 Senior Member

    verytricky..I think they are going on physicis,, and not boat application,but phyisics does requir the entire equasion to get a true answer,,,,,,I hope I spelled physicis right....longliner
     
  3. jehardiman
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    jehardiman Senior Member


    Not to take away from your truly laudable achievements, but the V24 class is designed around stock components for cost reasons, not overall efficency which was the start of this thread. A lot of speed problems can be solved by throwing horsepower at it, i.e. why the really fast guys run GT's.

    If we compare the modern V24 class (24', ~1150 kg multi-step, 320 nominal hp, 80 mph) with the original circa 1980 developmental Arneson (18' Arena Craft, ~1000 kg no step, 260 nominal hp, 78 mph) we can see that the single prop Arenson is slightly better in the efficency department ( 0.55 R/W vice 0.58) , even using a non-chopper blade. Big reason is that the Arneson can turn a bigger wheel, which always improves efficency. CR props are only advantagously used when it is needed to deliver more power with a fixed prop diameter, which is not the absolute case here.
     
  4. Verytricky
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    Verytricky Large Member

    Found it...
    On Volvo Pentas website. They claim the DPX was designed for speeds over 50 knots.....

    http://www.volvo.com/NR/rdonlyres/E...7CE5C1D9249C/0/DPX385_PD_DPX_my97_1996_en.pdf
     
  5. Verytricky
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    Verytricky Large Member

    1490kg....
     
  6. jehardiman
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    jehardiman Senior Member

    Wow, you're way over class weight....Have you ever considered leaving the trailer off....it might let you go faster....:D

    Class website (www.v24powerboats.co.uk) reports 1150 kg dry with a on trailer weight in the box of ~1500 kg. Ok so add in the 180 ltrs fuel for a wet weight ~1350kg
     

  7. Verytricky
    Joined: Oct 2005
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    Verytricky Large Member

    UIM rules since 2004.
    Since Pascoe got the rights to build, he could not get the strength required on the canopy by the UIM unless he made the boat heavier. So in 2003 the change was made, effective January 2004 that the weight of the boat as raced, at the end of the race, dry of water should be 1490Kg

    I actually lost a second place in Sweden in 2004 by being 4 Kg underweight, and was disqualified! The official results show 1486Kg ( DQ )
    :mad:


    The class website is (www.v24Club.com)

    The website (www.v24powerboats.co.uk) is a marketing website by the people who sell the boats.

    Both are out of date, but the class website (www.v24Club.com) has at least the 2005 rules.

    The latest rules are on the UIM website, but they list 1490 as the required weight.

    ( FWIW, I was weighed at the record attempt and was found to be exactly 1500kg! Exactly, not over nor under.. )
     
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