Small beachcat design

Discussion in 'Multihulls' started by nacrajon, Jan 10, 2009.

  1. nacrajon
    Joined: Jan 2009
    Posts: 18
    Likes: 1, Points: 3, Legacy Rep: 13
    Location: Australia

    nacrajon Junior Member

    Boat | NACRA 4.5 | NACRA 5 | NACRA F17
    Length | 4.50 | 5.0m | 5.2
    Width | 2.44m | 2.44m | 2.44
    Weight | 120kg | 130kg | 156 kg
    Sail area | 17.5m^2 | 19m^2 | 15.25m^2
    Spinnaker | Option | No | 17/19m^2
    People | 1-2 | 2 | 1
    Design | Skeg | Skeg | Dagger
    VYC Yardstick| 88 (no spin) | 81 | 72.5

    What's the primary reason the F17 is 15.5 minutes faster around the buoys than a 4.5 in 100 minute race?

    1. Waterline length
    2. Only 15% heavier with both having one crew, but spinnaker makes up for it
    3. Much faster to tack due to daggerboards
    4. Dagger boards allow it to point higher
    5. Higher aspect ratio sail
    6. F17 has experienced sailors, 4.5 a beginners boat
    Last edited: Jan 10, 2009
  2. robherc
    Joined: Dec 2008
    Posts: 432
    Likes: 5, Points: 0, Legacy Rep: 102
    Location: US/TX

    robherc Designer/Hobbyist

    I think #1 has a LOT to do with it (though maybe not a 25% boost!), and the longer waterline will help make up for a lot of weight difference with VERY minimal losses.
    I'm guessing that 3, 5, and expecially 6 prob. had a lot to do with it too though ;)
  3. Fanie
    Joined: Oct 2007
    Posts: 4,603
    Likes: 174, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    Longer boats are faster than shorter ones.

  4. cleblanc
    Joined: Dec 2004
    Posts: 26
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Sept-Iles, Quebec, Canada

    cleblanc Junior Member

    In this specific case, the waterline length has little impact on the speed around the course.

    The main reason that the F-17 is faster around the race course is that it is design to be fast on the upwind legs and on the downwind legs, the Nacra 4.5 and 5 are design as recreational boats.

    The high aspect ratio sails and daggerboards explain the improved upwind performance

    Hull design and Spinnaker explain the downwind performance.

    So points 5, 4 and 2

    On a beam reach the Nacra 5 would probably have a similar speed.

    You can look at the Texel rating page for some information on how the parameter are included into the handicap calculation

    The Portsmouth rating allows some modifiers
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