Inverted pilothouse windows

Discussion in 'Boat Design' started by calevi, Jan 24, 2024.

  1. calevi
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    calevi Junior Member

  2. CarlosK2
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    CarlosK2 Senior Member

    In a sailboat Upwind (Force 5 and above) the AeroDynamic Drag and the forgotten AeroDynamic Lateral Force of the Hull are very high figures;

    but the bulk is the heeled Hull.
     
  3. CarlosK2
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    CarlosK2 Senior Member

    Screenshot_2024-01-24-11-25-29-14.jpg

    In addition to the hull size (length and freeboard) ...

    it is necessary to take into account:

    1) the wind angle with respect to the bow
    2) the heeling of the yacht and
    3) the difference in wind speed with respect to the height

    Of course it is a different matter if the sailboat is motoring head to wind.
     
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  4. Will Gilmore
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    Will Gilmore Senior Member

    It looks like you are designing a cruising boat, not a racing boat. I would say, in response to,
    You would only ever notice when doing the numbers. Actually on the water, she should, all else being equal to another boat, sail well enough.
     
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  5. CarlosK2
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    CarlosK2 Senior Member

    Copy and Paste

    Boatdesign

    Hallberg-Rassy 36 pointing ability https://www.boatdesign.net/threads/hallberg-rassy-36-pointing-ability.57178/

    "Hi,
    I have a Hallberg-Rassy 36, a well known cruising design of German Frers . The boat is excellent in all points of sailing except upwind. I am not racing but I do have concerns for the safety aspects of poor upwind sailing in a cruising boat and the obvious risk of not being able to claw off a lee shore in bad conditions.
    The pointing angle (without pinching) to the true wind in light airs and flattish seas is acceptable (90/100 degrees between tacks). This is obviously the case when sailing with the full main and full genoa.
    It is when the wind pipes up and the sea becomes rough that the windward performance deteriorates badly"

    ...
     
  6. CarlosK2
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    CarlosK2 Senior Member

    Upwind

    Increasing the Angle with respect to the wind ... increases the surface area of the Hull exposed to the wind ...

    and increases A) the aerodynamic Drag and B) the forgotten aerodynamic Side force which further loads the daggerboard/keel

    and A+B) further increases the beating/pointing Angle ...

    and to top it all off, the Jib can't adjust/trim well to that Angle

    Perhaps the best thing to do at this point would be a boom, a Jib/StaySail boom, as in the mainsail.
     
  7. CarlosK2
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    CarlosK2 Senior Member

    Screenshot_2024-01-24-14-54-02-38.jpg

    It is a reality that the 'cruisers' do not go upwind when the wind rises, in fact in summer against the wind accelerated by the "Azores anticyclone" they climb the "Cape of St. Vincent" in Portugal by motor or sail aided by the engine.

    Most of the "sailboats" are in fact "motorsailer"
     
  8. CarlosK2
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    CarlosK2 Senior Member

    In 12-14 meters sailboats I do not know what solution could have.

    In small sailboats I think this problem can be solved with a combination of (A) 3/4 fractional rig (B) staySail with boom (C) sea water ballast tanks.
     
  9. CarlosK2
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    CarlosK2 Senior Member

    Screenshot_2024-01-24-15-22-40-41.jpg

    Reducing freeboard is NOT an acceptable solution.
     
  10. philSweet
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    philSweet Senior Member

    @CarlosK2 Yeah, not the way you want to do inverted windows.
     
    Last edited: Jan 25, 2024
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  11. calevi
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    calevi Junior Member

  12. CarlosK2
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    CarlosK2 Senior Member

    Screenshot_2024-01-25-11-35-26-36.jpg

    Sail Carrying Power: 28% (!!!) Displacement

    0.28 = GZ / h

    h = (h_Wind - h_Water)

    h_Wind: vertical position of Aero Force
    h_Water: vertical position of Hydro Lateral/Lift Force

    Hoist (jib + Main): 47 (!!!) Squared meter per Ton

    It doesn't matter what the windows of a cruising sailboat look like, it's an unimportant detail.

    The question is Drag and Power

    A Cruiser:

    Sail Carrying Power: 6-7-8% D
    Hoist: 10 Squared meter per Ton
     
    Last edited: Jan 25, 2024
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  13. CarlosK2
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    CarlosK2 Senior Member

    Screenshot_2024-01-25-12-11-27-44.jpg

    Hiding and burying the sailboat in the water was in the past a very good solution to reduce Hull Aero Drag;

    but it is not a solution for today's cruising sailboat.
     
  14. CarlosK2
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    CarlosK2 Senior Member

    IMG_20240125_123516.jpg

    1967 ...

    In the last century ... the cruelty of hiding the crew sweating below deck moving the big winches to reduce Aero Drag.

    This is an extreme.

    And the other extreme:

    The sailboat that came from northern Europe and capsize this autumn in Portugal drowning its four crew members: it had sails hoisted for summer in the Mediterranean and wind tarpaulins as if they were having dinner one night in port.

    ---

    In summary I think that for a modern cruiser of 12-14 meters there is no good solution to low Power and high Drag;

    but on the one hand not add more difficulties and, on the other hand, i am a strong supporter of the 'StaySail Boom'.

    Total, don't worry about the windows, IMO they are a drop in an ocean.
     
    Last edited: Jan 25, 2024

  15. CarlosK2
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    CarlosK2 Senior Member

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