Pocket cruising boats

Discussion in 'Sailboats' started by Guillermo, Apr 30, 2006.

  1. Nels Tomlinson
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    Nels Tomlinson Junior Member

    So Windvang, I'm curious. You were able to shave off two tons at the same strength by going from steel to kevlar. What did that do to the cost of the hull? Kevlar/foam composite is much lighter per unit strength than steel, but it also costs way, Way, WAY more per pound than steel, so unless you saved a lot on labor, I'd expect the cost went up?

    Obviously, there is no intrinsic value to a heavy hull; if your hull is strong enough but too light, you can always stuff in some more gear and supplies. Obviously, the lighter hull is going to be objectively better, but I'm wondering about the cost benefit ratio.
     
  2. Dyflin
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    Dyflin New Member

    A fascinating thread, thank you for all the input. :)

    I wonder if I could suggest some more boats for discussion.

    Elizabethan 30

    and here

    Also the Vertue 2

    Two more "modern" designs from well known manufacturers include worth considering are

    Westerly Merlin

    Moody 28


    Thanks again and keep up the great work :D
     
    Last edited: Dec 22, 2006
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  3. yipster
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    yipster designer

    hi Dyflin, ok nice boats and welcome aboard but use the upload (below text) option becouse we cant look into your HD :p
     
  4. Guillermo
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    Guillermo Ingeniero Naval

    Nice post Dyflin, thanks for the input on those very nice boats. Somewhat lazy these days, and also experiencing a home computer problem, I'll work on her numbers as soon as possible.
    Cheers.
     
  5. Guillermo
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    Guillermo Ingeniero Naval

    Also here: Any new design lately, deserving to be brought here?

    Cheers.
     
  6. mcm
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    mcm Senior Member

    Has anyone on this thread seen any building plans for a 26'-28', STEEL, blue-water, ocean-cruising, shoal-draft, centerboard, possessing full 180 degrees self-righting?
     
  7. Guillermo
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    Guillermo Ingeniero Naval

    It's better late than never. Here some numbers for the Elizabethan 39, Vertue 28, Westerly Merlin and Moody 32. Inputs as per Dyflin posted pages)
    (asuming Bwl as 0.9*Bmax)

    VERTUE II
    Length/Beam Ratio L/B = 2,92 (2*LWL + LH) / (3*Bmax)
    Lwl/Bwl Ratio Lwl/Bwl = 3,05
    Length/Draught Ratio Lh/T = 5,7
    Beam/Draught Ratio Bmax/T = 1,74
    Ballast/Disp Ratio W/Disp = 0,48
    Displacement/Length Ratio D/L = 418,71
    Sail Area/Disp. Ratio SA/D = 13,43
    Hull speed HSPD = 6,20 Kn
    Velocity Ratio VR = 1,03
    Capsize Safety Factor CSF = 1,49
    Motion Comfort Ratio MCR = 40,38
    Heft Ratio HF = 1,84
    Roll Period T = 4,44 Sec
    Roll Acceleration Acc = 0,03 G's
    Stability Index SI = 1,86
    Angle of Vanishing Stability AVS = 148 º


    ELIZABETHAN 30
    Length/Beam Ratio L/B = 2,79
    Lwl/Bwl Ratio Lwl/Bwl = 2,88
    Length/Draught Ratio Lh/T = 5,91
    Beam/Draught Ratio Bmax/T = 1,86
    Ballast/Disp Ratio W/Disp = 0,5
    Displacement/Length Ratio D/L = 231,12
    Sail Area/Disp. Ratio SA/D = 17,14
    Hull speed HSPD = 6,57 Kn
    Velocity Ratio VR = 1,12
    Capsize Safety Factor CSF = 1,92
    Motion Comfort Ratio MCR = 22,14
    Heft Ratio HF = 0,89
    Roll Period T = 2,61 Sec
    Roll Acceleration Acc = 0,1 G's
    Stability Index SI = 0,93
    Angle of Vanishing Stability AVS = 129 º

    WESTERLY MERLIN 28 (Twin)
    Length/Beam Ratio L/B = 2,55
    Lwl/Bwl Ratio Lwl/Bwl = 2,65
    Length/Draught Ratio Lh/T = 8,57
    Beam/Draught Ratio Bmax/T = 2,96
    Ballast/Disp Ratio W/Disp = 0,43
    Displacement/Length Ratio D/L = 261,89
    Sail Area/Disp. Ratio SA/D = 13,69
    Hull speed HSPD = 6,51 Kn
    Velocity Ratio VR = 1,04
    Capsize Safety Factor CSF = 2,01
    Motion Comfort Ratio MCR = 22,17
    Heft Ratio HF = 0,85
    Roll Period T = 2,53 Sec
    Roll Acceleration Acc = 0,12 G's
    Stability Index SI = 0,84
    Angle of Vanishing Stability AVS = 121 º


    MOODY 28 (Fin)
    Length/Beam Ratio L/B = 2,47
    Lwl/Bwl Ratio Lwl/Bwl = 2,59
    Length/Draught Ratio Lh/T = 5,51
    Beam/Draught Ratio Bmax/T = 2,01
    Ballast/Disp Ratio W/Disp = 0,38
    Displacement/Length Ratio D/L = 230,48
    Sail Area/Disp. Ratio SA/D = 15,25
    Hull speed HSPD = 6,47 Kn
    Velocity Ratio VR = 1,1
    Capsize Safety Factor CSF = 2,14
    Motion Comfort Ratio MCR = 19,02
    Heft Ratio HF = 0,74
    Roll Period T = 2,18 Sec
    Roll Acceleration Acc = 0,16 G's
    Stability Index SI = 0,71
    Angle of Vanishing Stability AVS = 124 º
     
  8. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    Hmm, I would guess that a long roll period like 4,44 seconds is good for comfort? Can you repeat what else goes into the comfort ratio?
     
  9. Guillermo
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    Guillermo Ingeniero Naval

    From Ted Brewer (http://www.tedbrewer.com/yachtdesign.html)

    "COMFORT RATIO (CR): This is a ratio that I dreamed up, tongue-in-cheek, as a measure of motion comfort but it has been widely accepted and, indeed, does provide a reasonable comparison between yachts of similar type. It is based on the fact that the faster the motion the more upsetting it is to the average person. Given a wave of X height, the speed of the upward motion depends on the displacement of the yacht and the amount of waterline area that is acted upon. Greater displacement, or lesser WL area, gives a slower motion and more comfort for any given sea state.

    Beam does enter into it as as wider beam increases stability, increases WL area, and generates a faster reaction. The formula takes into account the displacement, the WL area, and adds a beam factor. The intention is to provide a means to compare the motion comfort of vessels of similar type and size, not to compare that of a Lightning class sloop with that of a husky 50 foot ketch.

    The CR is : Displacement in pounds/ (.65 x (.7 LWL + .3 LOA) x B^1.333). Ratios will vary from 5.0 for a light daysailer to the high 60s for a super heavy vessel, such as a Colin Archer ketch. Moderate and successful ocean cruisers, such as the Valiant 40 and Whitby 42, will fall into the low-middle 30s range.

    Do consider, though, that a sailing yacht heeled by a good breeze will have a much steadier motion than one bobbing up and down in light airs on left over swells from yesterday's blow; also that the typical summertime coastal cruiser will rarely encounter the wind and seas that an ocean going yacht will meet. Nor will one human stomach keep down what another stomach will handle with relish, or with mustard and pickles for that matter! It is all relative."

    Cheers.
     
  10. yipster
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    yipster designer

    a us naval report mentioned a boat motion of 10 deg can set mariners capacitys back by 50%
    interestingly a 5% motion gave 110% capability ( was used in a multihull argument :p )
     
  11. Guillermo
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    Guillermo Ingeniero Naval

  12. gilberj
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    gilberj Junior Member

    Hi Guillermo, Thanks for bumping this thread. I had not seen it before. Interesting discussion. I note particularly the discussion of light displacement/shallow body boats. After a lifetime of sailing traditional keelboats I now have a light /shallow LFH Meadowlark. I have not had it offshore but been out several times in F8v@2-4M seas and once in F9 near coastal. It is the best behaved boat in those conditions I have sailed. That is partly due to the rig geometry
    I am curious about how you derive the roll acceleration numbers. The other factors I am familiar with.
     
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  13. Guillermo
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    Guillermo Ingeniero Naval

    Hi, gilberj!

    Roll acceleration formula (imperial units) is:

    (6,28/T)^2*R*(10*3,141592/180)/32,2

    Were:
    T (period) = =6,28*(I/(82,43*Lwl*(0,82*Bmax)^3))^0,5
    R (radius) = Bmax/2-1,5
    I (inertia) = =(Disp^1,744)/35,5

    Cheers.

    P.S. I have seen there are different sizes for the Herreshoff's Meadowlark. What length is yours?
     
  14. gilberj
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    gilberj Junior Member

    My Meadowlark is as the original design, 33 ft x 8'1"x 18" draft (slightly deeper than the design). Though I have seen photos of the larger ones, I do not know any spec details of the larger versions. I believe there were 35', 36' and 37' versions.
     

  15. Guillermo
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    Guillermo Ingeniero Naval

    Thank you gilberj.

    I would appreciate from Boatdesign.net's members and visitors posting here information regarding sailing boats in the market, under 8 m hull length and being commercialized as having Design categories B or A.

    Thanks a lot in advance. :)
     
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