Return of the Sailing Ship?

Discussion in 'General Science & Technology' started by exchemist, Aug 21, 2023.

  1. exchemist Valued Senior Member

    I thought this was interesting:

    Cargill has chartered a bulk carrier from China to Brazil, which uses this technology to cut fuel consumption by up to 30%. From the pictures, it looks like a set of aerofoils mounted on the forward half of the deck. Seems they are folded down in port. I imagine they would also be taken down in the event of storms at sea.

    One thing I am curious about is the degree to which they will make the ship heel and slip sideways when the wind direction is oblique to the direction of travel. They won’t want the cargo to shift and make it list.

    Here is the BBC article about it:
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  3. DaveC426913 Valued Senior Member

    1. The tech looks like it mirrors oldey-timey square sails, which are more about pushing than the aerodynamic lift to get from modern mail/fore sail design. (Modern main/fore sailboats experience the worst heel when heading into the wind.) I wonder if that lack of lift results in a lower degree of heel.

    2. Modern ocean liners have active fin stabilizers for reducing heel in rough seas.

    Ship stabilizers (or stabilisers) are fins or rotors mounted beneath the waterline and emerging laterally from the hull to reduce a ship's roll due to wind or waves. Active fins are controlled by a gyroscopiccontrol system. When the gyroscope senses the ship roll, it changes the fins' angle of attack so that the forward motion of the ship exerts force to counteract the roll.
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  5. exchemist Valued Senior Member

    I'm pretty sure they are aerofoil sections. Some of the pictures in the first link show this, I think.

    Good point about fin stabilisers. I don't think these are routinely fitted to cargo ships but it would indeed help counteract the heel from the wind, especially as the engine will still be running, giving the vessel a certain minimum speed through the water, regardless of how much propulsion the wind is providing. Actually, I've found this from Wärtsilä: which seems to confirm stabilisers are not routinely fitted to cargo vessels, though there is an argument for doing so. Perhaps indeed they are fitted to this ship.

    As you say, the heel will be most pronounced when beating into a wind on the port or starboard bow.
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  7. DaveC426913 Valued Senior Member


    Right. I hadn't thought of that. Since they are 3-dimensional aerofoils, they are able to generate their own lift without the need for a foresail to shape the airflow.

    Yes, that was my hypothesis.
  8. exchemist Valued Senior Member

    By the way, are you sure about square-rigged sails? I had understood those too were aerofoils, with a leading and a trailing edge, the spars being braced round to allow the wind to flow from one side to the other.
  9. sculptor Valued Senior Member

    a few years ago we had the beluga with the sky sail(kite)

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    which claimed a 20% reduction in fuel required.
  10. DaveC426913 Valued Senior Member

    I guess it depends on what were talking about.

    Historically, square-rigged sails are symmetrical about the mast, are they not? How could they have a leading and trailing edge, unless taken down and flipped?

    Also, a 2-dimensinal sail, even a curved one, may have a camber, but it doesn't have a thickness. Isn't that why a foresail is necessary? (I realize this is reaching the limit of my nautical know-how.)
  11. billvon Valued Senior Member

    Well, all sails do both. Modern sails are optimized for close haul and close reach points of sail because they are faster, while older sails are optimized for broad reaches and running. But both lift and drag are always part of it.

    Yes, the degree of heel will depend on keel design, weight distribution and any active measures (like stabilizers.)
  12. exchemist Valued Senior Member

    My understanding is that, on a reach, for instance, or even more when beating, the spars, which can pivot about the mast, would be braced to allow the wind to flow across the sail from the upwind side of the vessel to the downwind side. The natural belly of the sail would provide an aerofoil section, in spite of the rigidity of the spar. The spars could rotate up to 45deg or so either side of the central 90 deg position.

    There seems no doubt square riggers could beat into the wind to some degree. So they cannot have simply relied on the sails acting like a spinnaker and blocking the wind.

    As for foresails, my laser and many other dinghies, not to mention windsurfers, have only one sail. You get an aerofoil section from the natural curve of the fabric, when it is filled by the wind. In that case the leading edge is at the mast. With a square sail it would be the windward edge of the sail.

    Here is a picture of a square rigger with the spars braced round:
    Last edited: Aug 22, 2023

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