Is this too much flam??

Discussion in 'Sailboats' started by mcm, Apr 18, 2017.

  1. graywolf
    Joined: Dec 2014
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    graywolf Junior Member

    Actually, flam and flare refer to the bow of the boat, at least according to Howard Chapelle.

    Flam is that rounded shape, while flare is the tulip shape.

    If you look at photos of Lymon boats of the 1950's you see flam, while Lymons of the 1960's are flared. According to Chapelle flam is more seaworthy in heavy seas, and flare deals better with chop. The reason is because the rounded bows raise quickly to the waves, while the flared bow cuts through chop better because of the finer lines. In a two-foot chop flam will pound your fillings out, and in six-foot waves flare will bury your foredeck.

    Quite obviously a boat running around at high speeds on small lakes needs to deal with chop. Boats running offshore need to be able to deal with high seas. Now, I guess from a designers point of view, what is the best compromise is the question?
     
  2. messabout
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    messabout Senior Member

    Posted by Graywolf; If you look at photos of Lymon boats of the 1950's you see flam, while Lymons of the 1960's are flared. According to Chapelle, flam is more seaworthy in heavy seas, and flare deals better with chop. The reason is because the rounded bows raise quickly to the waves, while the flared bow cuts through chop better because of the finer lines. In a two-foot chop flam will pound your fillings out, and in six-foot waves flare will bury your foredeck.

    I am not one to argue with the likes of Chapelle. However, a blanket statement such as the above flam/flare analysis is humbug. There are so many variables in dimension and section form as to make such claims a bit reckless.
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    The "flare" being referred to must be hollow flare, concave in section, and the "flam" just straight sectioned, but with an angle to the vertical. As Messabout says, it is not much to go on, in the whole picture. Some boats that are quite full bowed down low, still have substantial hollow flare, like the old Bertrams. One possible objection to hollow flared bows on fast boats is the generation of unwanted aerodynamic lift right forward, and there is also the ability to gain a little more interior space by dispensing with the hollow. Hollow flare has been out of fashion for some time on planing boats, a well raked bow acts to dampen spray, as well or better than a more plumb bow with hollow flare, too.
     
  4. Dolfiman
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    Dolfiman Senior Member

  5. Dolfiman
    Joined: Aug 2017
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    Location: France

    Dolfiman Senior Member

     
  6. Dolfiman
    Joined: Aug 2017
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    Dolfiman Senior Member

    Here is my own tentative to draw your mid section and the hull itself with your data, using my application "Gene-Hull VE double ended" (dedicated to the generation of hull for double ended sailing yacht, a geometric+parametric approach for early stage design that I have just finished to develop).
    I can respect all your figures, Boa 2,74 m, Bwl 1,98 m, Free board at mid section 0,84m, draft hull body 0,61 m and quite same beam at 1' below the waterline : I obtain 1,57 m close to your 1,56. For the hull itself, I took Lwl 15m + some overhangs for an Loa of 16,5m (?), a light displacement (with standard keel and rudder) of 8,25 t (a bit below yours 9t, >> Lwl/D(2/3) = 7,6) and a mid-range Cp of 56,4 %.
    At 25° heel angle (in hydrostatic conditions, iso displacement, fixed trim 0°) , the elevation of the hull is 5 cm, the transverse offset of the CB is 19 cm a bit less than yours 24 cm, the longitudinal offset of CB is very low as you expected (6 cm backward >> 0,39% Lwl). Other data in the document joined, I put also the application itself and the User guide.

    As regard dynamic behaviour and seaworthy, I just can say that a L/B ratio of 6 (16,5 / 2,74) is very high and unusual for a 16m boat with oceanic sailings in its program, can you consider instead an L/B of 5 and you still can be slender, light displacement but with more room for accomodations and more hull volumes and righting moment to deal with wind and oceanic waves. See for example the Eagle 54 of Leonardo yachts, but with less overhangs if you prefer : Leonardo Yachts - eagle54 http://leonardoyachts.com/en/eagle54.html ;
     

  7. Dolfiman
    Joined: Aug 2017
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    Dolfiman Senior Member

    Following my previous message, this version attached to illustrate what could be the hull with an L/B close to 5 , so with a max Beam of 3,30 m instead of 2,74m while keeping Bwl/B = 0,72 and the corresponding flam. I put a bit more freeboards and overhangs (mostly aft), Loa is now 17,25 m and overall displacement (with standard keel bulb and rudder) is 9,47 t. All other data in document pdf joined + the "Gene-Hull VE double ended" application with this new set of input data.
    By hoping this can be helpful for you,
     
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