A72 Maximum Weight Limit Rationale

Discussion in 'Sailboats' started by DCockey, Jul 11, 2013.

  1. DCockey
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    DCockey Senior Member

    What is the rationale for the maximum weight limitation in the AC72 class rules?

    Do other development classes or box rule classes have a maximum weight limitation?
     
  2. Doug Lord
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    Doug Lord Flight Ready

    Might get better response in the "multihulls" forum? Probably limiting maximum righting moment......
     
  3. sharpii2
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    sharpii2 Senior Member

    I don't think they mean maximum weight. I think they mean minimum weight.

    Only one number is posted, probably because it is assumed that everyone will make their boats as light as possible.

    A heavier multihull has no advantage over a lighter one of the same dimensions.
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    I must say Doug, I am shocked by your reply. For someone who keeps referring to ‘rules’ or ‘facts’ and quotes by those in the AC Fraternity as being the oracle of such information, surely something as basic as this should be known to you?

    It is rather like an outspoken TV football pundit on a weekly football round up show being asked to explain what is the offside rule, yet simply hasn’t a clue how to respond! :eek:
     
  5. Doug Lord
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    Doug Lord Flight Ready

    sharpii2, the limit is on maximum weight(and minimum weight). In fact, the new rules which were just thrown out had something like a 200kg INCREASE in the maximum weight. Limiting maximum weight limits maximum RM.
     

    Attached Files:

  6. daiquiri
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    daiquiri Engineering and Design

    Section B, item 5.10 of the AC72 Class rule:
    "The sailing weight shall be between 5720 kg and 5920 kg."​

    It has to be read together with the sail area limit, and with the limitations on length and beam.
    When you put them all together, they are telling "we want to see boats as similar as possible, yet not a one-design."

    Cheers
     
  7. sharpii2
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    sharpii2 Senior Member

    Thanks for the link.

    Though it is true, maximum righting moment increases with with more weight, especially on a multi, a muli's speed, like that of most sailboats under most conditions, is a function of RM/W.

    A boat with a high RM and low weight will almost always be faster than one with a high weight and consequently higher RM, if the boats are both either mono's or multi's and are of roughly the same length.

    In choppy conditions, the heavier boat sometimes has an advantage, as it has the momentum to plow through the chop. But this is of little comfort on a down wind run, when the lighter boat blasts past you.
     
  8. tspeer
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    tspeer Senior Member

    The reason was to avoid wide disparities in righting moment, which could lead to wide disparities in speed. The intent of the AC72 class rule is to control all of the major speed-determining factors so that the racing would be close.

    San Francisco, being a windy venue, could make having a heavier boat be faster, especially as the AC72 is over-powered to begin with. If the boat was under-powered, like the C-class catamarans, then the premium would be on achieving minimum weight.
     
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  9. jehardiman
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    jehardiman Senior Member

    Very true.
     

  10. MikeJohns
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    MikeJohns Senior Member


    ULDB multihulls particularly have a detrimental Pitch RAO in common wave spectra that can slow them considerably.
     
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