How bad are these hardchined catamaran hulls?

Discussion in 'Multihulls' started by Brorsan, May 2, 2012.

  1. Brorsan
    Joined: Nov 2007
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    Brorsan Junior Member

    I'm considering to buy a Dacapo 21 catamaran, a rather slow but cheap catamaran of 7.5m x 3.7m (and probably around 900kg). There are similar boats with rounded hulls and I wonder if i sacrefice much by these hard chined ones. Guess the water will not allways flow in the direction of the chine.
    I've been told by the seller of the cat that this is an evolution of the rounded version (dacapo 20) to get a faster boat, but it doesnt sound logical to me.

    Appreciate any thoughts and comments.

    /Brorsan



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  2. Richard Woods
    Joined: Jun 2006
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    Richard Woods Woods Designs

    I don't think you will sacrifice much speed. But you will sacrifice a lot of time and money fixing rot (at least as far as I can tell from the photos). It had better be really cheap and I hope you only plan to daysail on gentle days

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
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  3. Petros
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    Petros Senior Member

    There is not a lot of difference in performance in similar designs of hard chine vs. round. There have even been a few instances of the hard chine version of the same boat being faster (less drag).

    The theory is round hulls will have less whetted area for the same displacement (and less drag). But I suspect there are often unrecognized advantages (besides being easier to build), that may give a performance improvement in certain conditions.

    Hard chines can direct splash away from the side of the hull in rough conditions for example, and result in less drag when at speed. I know from tanks tests that different shape hulls of otherwise identical designs will have very different performance when in smooth vs. rough water. Also, hard chines will come up on plane much faster with less drag than round hull boats. Not likely to happen in a heavy cruiser, but still something to consider about over generalizations about hull design.

    So it is hard to make a blanket rule. If the boat you are buying is well designed and well built, it will perform fine and serve you well no matter hard chine of round hull. A few fractions of a knot difference will not even matter unless you are hard racing identical boats, for recreation use, I would not worry about it.

    It is not a reason to buy or not buy a boat.
     
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  4. Brorsan
    Joined: Nov 2007
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    Brorsan Junior Member

    Thank you for fast and good replies.

    /Brorsan
     
  5. garydierking
    Joined: Sep 2004
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    garydierking Senior Member

    I would worry much more about the underwing clearance than the chines.
     
  6. warwick
    Joined: Jan 2012
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    Location: papakura south auckland new zealand

    warwick Senior Member

    Would the bridge deck clearance also to do with the size of the boat at 7.5m. You just do not have the length for a high bridge deck clearance. Unless you want a tower block on water.

    Would it be dependant on intended use.
     

  7. Brorsan
    Joined: Nov 2007
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    Brorsan Junior Member

    Yes, the bridgedeck clearence is the biggest consern (low buoyency in the bows is another),
    But with a limited budget and very few used multihull-designs in the swedish market there is not many options. The boat is not rotten, just dirty with badly maintained finnish.

    Some boats have made the bows longer to increase forward buoyency, but i guess it is not possible to increase bridgedeck clearence without mayor surgery.
     
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