McGowan's 23' Tri 'Zip '

Discussion in 'Multihulls' started by Marvout, Sep 4, 2010.

  1. Marvout
    Joined: Aug 2010
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    Marvout Junior Member

    I just stumbled onto McGowan's 23' Tri - Zip. Nice renders of an interesting hull.

    http://www.mcgowanmarinedesign.com/Zip_Tri.html

    I'm curious about his main hull. Why is that I don't see more main hulls with that kind of shape. I speaking particularly to the straight line from the waterline to the deck line. I think the SeaRunners and the Constant Cambers have that similar kind of constant flare of the main hull. Buccaneers and Kurt Hugh's have a very vertical/straight hull with no flare and a wide cabin placed on top. Farrier's and Kendrick's have a more elaborate concave sides that flare out quite significantly at the top of the hull. Is there a significant advantage to a concave main hull side? I'm wondering why I don't see more Trimarans with a constant flared hull like McGowan has drawn?

    Marvin
     
  2. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    Thanks for the link! Interesting boat designed to fly the main hull-thats cool. Not being able to trailer it may hurt sales...


    LOA 23'

    rendering from McGowan site in post#1:
    (click on image)
     

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  3. idkfa
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    idkfa Senior Member

    Marvout, imo there will be little performance difference in flat seas, but once the waves were riding up the sides of the hull, then wave drag will increase to that of a monohull ie wider hull.
     
  4. Doug Lord
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    Doug Lord Flight Ready

    Designed to Fly

    By that time it will probably be flying the main hull....... I would think that would eliminate any problems associated with the flare.
     
  5. idkfa
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    idkfa Senior Member

    Sorry Doug, but foils don't work as advertised in waves either.
     
  6. Doug Lord
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    Doug Lord Flight Ready

    Designed to Fly

    Well, lets see: Banque Populaire, Sodebo, Groupama, USA 17, and almost every single ORMA Tri used/uses curved foils for ocean racing. I wouldn't think that whether this particular boat had curved foils in the ama's or not would make a huge difference on whether it flew the main hull or not. Probably goes faster with the foils and maybe flys the main hull slightly earlier with the foils but it is the flying of the main hull due to heeling that keeps the flared sections out of the water a whole lot of the time-probably especially in waves.
    Again, the foils are not the reason the McGowan boat flys the main hull..

    BMW-O with curved foils, IDEC with curved foils, Sodebo before it had curved foils:
     

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  7. jamez
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    jamez Senior Member

    The main hull shape you refer to is not uncommon. Its is similar to the L7. http://www.multimarine.com/designdetail.php?id=1

    A hull flare or step gives increased interior room but still allows a reasonably narrow waterline. Downside is thet they are more complex shapes to build which adds time/money and may require a particular building technique. The seaclipper 28 is another design that has a similar config., has small interior space, but is reportedly a really straight-forward build. Ya makes ya choice, all boats are compromises.

    Edit:6 Sept; SC 28 similar config other than the flat bottom.
     
  8. Marvout
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    Marvout Junior Member

    I wish I could see better drawings of the L7. I see quite a bit of mention of it, but I find it quite hard to compare it to other boats if all I can see is 3/4 view renders. Plans/Profiles anywhere?

    For comparison, at rest it looks like a Scarab 22 has about 9 1/2" before it begins to flare and an F22 has 8 1/4". So after waves of about a foot, these boats would begin to encounter increased resistance. I wonder at that point and above, how different the resistance would be for a constant flared hull that would imply a constant increase in resistance and a concave flared hull that would imply a dramatic increase in resistance when the water start smashing into the upper parts of the body after it has had that extra free running space.

    Marvin
     
  9. pogo
    Joined: Mar 2010
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    pogo ingenious dilletante

    No.
    The Zip`s flares are underwater, that`s totally uncommon.
    It`s weired.
    The designer calls them "sprayrails".
    Nice idea, but.....
    Have you noticed the rocker of the floats and mainhull ?
    The sprayrails in the aft-sections have a negative angle of attack.
    Does the designer wants the boat to sail always in a bow-up attitude ( with the help of the bananafoils ), planing on the aft sections/sprayrails ?

    A boat with a lot of contradictions.


    pogo
     
  10. luckystrike
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    luckystrike Power Kraut

    Rockerline of the Amas

    A friendly Hello to Everybody!

    I don' see the problem of this Tri in the flared mainhull with trapezoid bulkheads. This may work, even if there is a little more resistence in a choppy wave. Eric Lerouge ist designing them the also. I count on, that the main hull WL length/beam Ratio is 9:1 or better.

    What I fear is that the rockerline of the ama has to much curve in it, so that there is not enough longitudial stability in it to preserve hobby horsing or even nosediving when flying the main hull. Make compares to the catri foilers with there foiling systems that work quite well in flat waters. They have a second foil at the stern of there amas to stabilise the boat.

    Assisting foils on small multihulls may cause bigger problems than on a 60' Tri, because the main problem of foils is ventilation and therefore the total loss of its lift. A 2' wave for a 60 footer is nothing but a 23 footer will jump out of the water from it.

    If I'am going to put thousends of hours and Euros into a boat to build it, I would choose a real experienced multihulldesigner and not someone who reguarly designs traditional character boats coming up with questionably design details.

    Grrreetings from the North Sea Coast, Michel
     
  11. jamez
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    jamez Senior Member

    I was referring to the overall shape of the hull which is flared from the waterline out to the gunwale in a similar fashion to a CC26, or the other boats mentioned. To be honest I hadn't even noticed the little spray rail. I don't see the point in having one under the waterline. It strikes me as extra work for little return and i would assume add drag until the main hull starts to lift. Hopefully someone will build one and we can all see how it goes.
     
  12. pogo
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    pogo ingenious dilletante

    Not really.
    A small trimaran with the same empty weight, sailing on one Ama , supported by a foil, with the crew trapezing, will have much less comfort and look like this boat (designed in 2006 ; pre-bananafoil era):

    http://www.exploder.info/eng/content/view/19/125/

    pogo
     
  13. Doug Lord
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    Doug Lord Flight Ready

    ------------------------
    Not sure I understand what you mean by "Not really." Please help me to understand.
    While I've always liked the Exploder it does have a very high angle of heel when the main hull is just barely flying.
    I don't have enough other detail about the new boat(Zip) to check the designers claims much further so based on those claims "it is designed to fly the main hull" and I think that is cool. I was able to determine that with the rig shown on the site it would take a lot of wind to fly the main hull. I don't know about that on the Exploder-I'll check the specs again when I have time.
    The Exploder is trailerable-and I like that-what ever happened to that project-do you know?
    Neither boat has the crew trapezing??
    One thing is absolutely for sure: a tri that flys the main hull does not have to be uncomfortable.....

    ---------------
    Zip=28sq.m upwind SA
    Exploder=65sq.m upwind SA(!)

    Picture-Exploder with folding seat for skipper:
     

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  14. Eralnd44
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    Eralnd44 Wanderer

    This is told many times here. why such importance to fly main hull? Does it not make danger more closer. boat can also be fast having no cares of this flight. perhaps to much making of the one thing.

    Eral
     

  15. pogo
    Joined: Mar 2010
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    pogo ingenious dilletante

    All Tris that are designed to fly their mainhulls for longer periods have less comfort than normal tris of the same size. In smaller sizes they are mostly also designed for calmer/coastal waters.
    For flying the mainhull constantly the boat must be very light (or thru excessive sailarea very nervous), that doesn`t match with comfort, will result in a racer.

    By the way, have you ever sailed a not uncomfortable tri , flying the mainhull constantly ?

    pogo
     
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