Round full blunt bow on a cruising catamaran

Discussion in 'Multihulls' started by valery gaulin, Jan 20, 2017.

  1. valery gaulin
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    valery gaulin Senior Member

    I would like to know if someone has experience with a round full blunt bow on a cruising catamaran. A bow kind of like the new mini 6.5m bow or the dutch barge bow. Basically inceasing the prismatic coefficient. I know there is an optimum primatic coefficient for a centain hull speed to be repected for efficiency but i also have red that overshooting prismatic coefficient is not that armfull for a catamaran.

    It seams to be something to try to increase loading capacity for a small 30ft crusing catamaran. Prevent hobby horsing and also pitching.

    Could it be enought to help surfing? Maybe!!! Adding some fun...

    It probably would push more the water than slice it.The penalty might be worth the confort and advantage for a small cruising catamaran.

    Just want to know if someone was bold enought to try it?

    Catamaran hull size in mind is about 30foot long x 3.75foot beam with a blunt round bow with a prismatic coefficient of around 0.8.
     
  2. upchurchmr
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    upchurchmr Senior Member

    You are going to get a big shock when you hit a wave and a big pitch moment.
     
  3. waikikin
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    waikikin Senior Member

    & then for limited cost as a void area just make it 32-33' long & pointier....
    Then be the proud owner/designer of something much more good..
    Jeff.
     
  4. valery gaulin
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    valery gaulin Senior Member

    @waikikin: Hahahaha good reply! But 3 more foot of marima fees!!!

    When someone is thinking about a 30 foot x 14 foot beam cruising catamaran it is because budget is an issue. Otherwise i would just get a 45 foot long x 20 foot beam crusing catamaran!!!

    I was just wondering if someone tried to make a full round bow catamaran to see the behavior of such a design on a catamaran. It seams to work well for the mini 6.5 sailboat.

    Someone must of tried it somwhere on a catamaran! I am just trying to learn from other people mistake before I make them myself.
     
  5. upchurchmr
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    upchurchmr Senior Member

    No one has any experience because this is a really bad idea.

    I suggest you make your own test.

    Make yourself a 16' canoe with the same shape and see how it paddles. You can always find a more conventional canoe to test against.
    This will be really cheap compared to making the full size boat.

    IMHO, you would get a better boat and more interior space with a monohull. Probably faster also.
     
  6. redreuben
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    redreuben redreuben

  7. Mr Efficiency
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    Mr Efficiency Senior Member

    The resident catamaran expert Ad Hoc is always at pains to point out the much lesser importance of bow shape to resistance, than such things as length/displacement ratio and length/beam ratio, so I doubt there will be a dramatic effect with a blunt bow, particularly at modest speeds.
     
  8. waynemarlow
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    waynemarlow Senior Member

    The LR6 designed by Richard Roache is just such a design that pushes the shape at the bow into a very full but hydrodynamic shape. The idea being that it will wave pierce but due to the shape will act as a foil when immersed.

    http://lindahlcompositedesign.weebly.com/lr-6.html

    [​IMG]

    [​IMG]
     
  9. valery gaulin
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    valery gaulin Senior Member

    This is what I have in mind for round blunt bow, for a small cruising 30ft X 14ft catamaran. ''Cruising'' Not Racing!!! High volume, so that it does not suffer too much from overloading. Bow entry would not pierce the water like a pointy hull but rather try to climb up on top of the water or push the water at slow speed. The hull shape might be able to go up on surf while going down a wave on a beam reach. This hull shape would not allow a lot of lateral resistance therefore it needs a very good daggerboard or centerboard to counter leeway and give a somewhat descent upwind sailing capability.

    Now would this shape be prone to heavy pounding??? My intuition would be that if the wave frequency is short, yes. But if the wave frequency is high, No.

    I think that this hull shape would be outperform for sure in flat water by a nice fine entry bow shaped hull but the lost in efficiency in flat calm water might be worth the extra loading capacity of a small cruising Catamaran.

    I was watching a comparison on youtube about SUP displacement hull vs SUP planning hull. The conclusion was that in flat water the displacement SUP was faster while only paddling but as soon as the wave and wind pick up the planning SUP would be able to surf for certain stretch because the bow would not burry under water and the wider beam of the board. At the end the planning SUP was a better choice when wave and wind pick up. I hope everybody understand that you can't really plane on a SUP by only paddling, it needs to be a combination of paddling, wind and going down a wave. Therefore the comparison might be good since I don't think it is really possible to plane with a cruising catamran, but might be able to get a little bit on a surf if the beam of the hull is enought while going down a wave similar to the SUP planning hull regime.

    Also it probably would not be prone to hobby horsing and/or nose pitching being a full round blunt bow.

    Having no experience at all in catamaran design, am i totally out of wack thincking this behavior of such a hull.



    Capture d’e?cran 2017-01-22 a? 1.44.27 PM.jpg

    Capture d’e?cran 2017-01-22 a? 1.44.39 PM.jpg

    Capture d’e?cran 2017-01-22 a? 1.44.48 PM.jpg

    Capture d’e?cran 2017-01-22 a? 1.44.55 PM.jpg
     
  10. upchurchmr
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    upchurchmr Senior Member

    Yes you are.
     
  11. Tom.151
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    Tom.151 Senior Member

    Perhaps you could help us understand better why you need such an extreme departure from proven, safe proportions in what you prescribe.

    Since people cross the Atlantic with a 21' catamarans, and go around the world (via the Panama route) in 30 foot cruising cats -- what is it about you perception of your needs for extremely high load carrying capacity for your intended use?

    For sure, when sailing, most skippers would never load the ends of their boats (especially multihulls) with gear, and no one would enjoy sleeping in the ends either.

    PS... the use of the blunt bow in some Mini6650 boats is a very distinctly different situation. Look at sailing pictures of those successful boats and you'll see that the sailing waterline is well aft of the blunt bow. So it is doing nothing for load carrying - which is what you're trying to apply it to. Apples and oranges.

    Cheers,
     
  12. UpOnStands
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    UpOnStands Senior Member

    voila, the marine box for 2
     

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  13. valery gaulin
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    valery gaulin Senior Member

    UpOnStands Awsome!!! Can you make it for 4??
     
  14. UpOnStands
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    UpOnStands Senior Member

    that is one hull so two hulls plus deck = 4
    sleep head to head in each hull.
    only works as a catamaran of course. :D
     

  15. valery gaulin
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    valery gaulin Senior Member

    UpOnStands imagine a trimaran, 3 hulls = 6
     
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