Why do Classic Wooden Sailboats have a low freeboard design?

Discussion in 'Boat Design' started by Alson An, Jul 16, 2018.

  1. TANSL
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    TANSL Senior Member

    @DCockey, it is not a matter of complying with any regulation but of making the ship operative in any circumstance of those indicated by its SOR. I did not think it was necessary to have to explain this. but I do not care, here we are all to talk, to learn, to teach to those who do not know and to enjoy the forum.
    Do you think it is not important that a boat does not put the deck under water before it is due? Well, if you believe that, I have nothing more to say to you.
     
    Last edited: Aug 5, 2018
  2. gonzo
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    gonzo Senior Member

    Check any of the traditional workboats before any regulations about size, and they will show how they evolved based on use rather than laws.
     
  3. Ad Hoc
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    Ad Hoc Naval Architect

    If the naval architect doesn't know the dimension of his/her own design - who on earth does??!! :confused:o_O:rolleyes:
     
  4. gonzo
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    gonzo Senior Member

    Traditional workboats pre-date naval architects.
     
  5. Rurudyne
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    Rurudyne Senior Member

    Yep. Chappelle and others did good by just tracking down some of those old boats and measuring them before they finally disappeared. Even to this day many boats are made by eye by men who've made a, um, boatload of them.
     
  6. gonzo
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    gonzo Senior Member

    I think that they were usually specialized for one type of use and geographic area. New pleasure boats are designed to be a floating swiss army knife
     
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  7. TANSL
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    TANSL Senior Member

    Surely you have understood me and you know perfectly well that that has absolutely nothing to do with what I am saying in this thread, but ... each one is as it is and handles his frustaries as he sees fit. Allow me to laugh with all my strength of your comment. I know perfectly what is behind it.
     
    Last edited: Aug 5, 2018
  8. MikeJohns
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    MikeJohns Senior Member

    Draft limitations of the home ports was a big factor in design for geographic areas.

    Do you know much about the Gloucester fishing schooners? Classic lovely looking low freeboard sailboats but I remember there were many calls at the time to regulate their designs as there was a staggering loss of life over a few decades in the mid to late 1800's.
     
  9. Dolfiman
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    Dolfiman Senior Member

    At the early stage phase of the design process, one can consider the sailing yacht heeled at 30° and check that the sheer line is still above the water surface. This check can be done from the hydrostatic equilibrium (at iso-displacement and LCB = CdG), see attached two extreme examples, one for a classic 6M JI , one for an Imoca 60.

    It is based on the idea that, when sailing upwind :
    - the sweetspot heel angle, for which the boat can (should) reach its peak speed on calm water (usually Froude(Lwl) = 0,35), should be around 25° at the max. Beyond this heel angle, the speed does not increase anymore or decrease as you are limited by the righting / heeling moments balance while the drag increases. A first reefing is necessary to continue cope with an increasing wind speed.
    - ... and to add a margin of about 5° to this angle to cope with gusts of wind >>> ~ 30°
    - this is also an usual frontier between pleasant and unpleasant angle for the comfort of sailing on a keel boat.

    I think that for modern yachts, the sweetspot angle is about 22° to 25°, while for classic slender yachts it is more 25° to 28°

    In a second step of the design process, other objectives or constraints (more volume in the cabin, …) can be considered to increase this minimum freeboard.
     

    Attached Files:

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  10. Rurudyne
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    Rurudyne Senior Member

    Small digression:

    This caused me to think (and it didn't hurt a bit *bada*boom*kisk*) about Top Gear ... did they ever try to build a Super-Sport RV ... or just a very fast RV? I know they raced buses. I thought of this because of these high performance luxury yachts that are basically just that on water, if not Super-Sport Houses, which are very much efforts to have it all in one (like Swiss Army Knives) and owners pay at the pump for the option.

    I'm also sorta reminded of a lady talking about the only time anyone ever tried to ski behind Thunderbird ... a stunt the Top Gear folks probably would have loved.
     
  11. gonzo
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    gonzo Senior Member

    Yes, they had about 10% yearly attrition of the fleet, but the profits were large enough to justify it. There were two main modifications to make them safer. One was to make the bowsprit tilted up, which helped crew from getting submerged and washed overboard. Another was to increase the bow overhand , that shortened the bowsprit with the same safety advantages.
     

  12. MikeJohns
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    MikeJohns Senior Member

    Thanks for that, I'm just looking at them now and I see the losses are staggering. And not just men being washed off the boats as an annual attrition, but the loss of the vessels themselves when they encountered heavy weather:

    In 1862, 15 vessels and 120 men lost in a gale.
    In 1871, 19 vessels and 140 men.
    1879 14 vessels and 157 men in February gales.
     
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