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Re: [AWES] Large Sailing Ships as MegaScale AWES Similarity Case

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  • dave santos
    Hi Chris, Wow, the Royal Clipper is a recreated wonder (if not exactly a clipper). Wind Star class boats are banal by comparison, but all modern sailing ships
    Message 1 of 5 , Jan 15, 2013
      Hi Chris,

      Wow, the Royal Clipper is a recreated wonder (if not exactly a clipper). Wind Star class boats are banal by comparison, but all modern sailing ships show an amazing reduction in crew need compared to the Golden Age of Sail. My guess is that the image-conscious cruise lines tend to replace sails when they look dingy and patched, rather than when they are truly worn out. I looked at global UV, and Roddy seems to live in the best place of any of us (Isle of Lewis), with 1/5 the UV of tropical hot-spots. In a low-UV location, sails might be more fatigue limited than UV vulnerable.*

      The guess of 10MW "equivalent rating" for a windjammer class boat is looser still, since HAWT ratings are based on wind higher than "most probable" wind for most locations. "10" was rounded up to help calculate with fingers and toes. We know also, that near Hull-Speed, engine or sail power can double, but you don't get much more speed, although more power extractable by, say, towing a second hull or turbine ( a grunt-power mode).

      As for the modular sail units characteristic of these ships, Mothra kite design sizes the tarp sails in manageable units below the likely failure-prone unit-scale. This "divide and conquer" design strategy has key advantages in localizing damage to a single unit, as a rip-stop feature, and also enabling quick easy replacement (even hot-swapping aloft someday soon). Since Drag-Force is a major classic kite principle, the sail can blow out of shape quite a bit without excessive loss of power. We know that some creep of our polymers only makes them better performing, which is why slowly prestretched kitelines are preferred. It may be that we someday rotate Mothra sails according to this lifecycle effect.

      You mention "stress distribution" of  big rigs. The Mayan hammock is a good model of a (human-rated) tensile net that passively distributes loads in a highly optimal way, by its diagonal Bias Construction. In our favor, the larger the kite, the smaller the characteristic turbulence scales, which means most disturbances are subscale, and cancel. There are many other megascaling fudge-factors and caveats, such as the design option to reduce frontal solidity (increase porosity), and reducing sail (furling) during storms, but our modern cloth materials are truly amazing, over an order of magnitude stronger than cotton and wire rope by weight, which is way-strong. 

      Where it gets exciting is that the (crudely) calculated scaling limits of a Mothra rope-loadpath network (the "rigging") in a tree-like branching pattern seem to at least match or even exceed the troposphere height scale of about 10,000m. This is the wonder of scaling a quasi 2D structure in our 3D world. There is a progressive scaling limit, but it gathers slowly.

      Its our sail handling ability that seems to scale-limit us more than anything. We may need winches power-rated beyond any machinery yet devised, although a lot can be done by a line pay-out strategy ("push" turning, trimming) and cascaded killing. We know some "power-amplifier" mechanisms made by rigging methods.

      It must be wonderful to sail on even the more soulless modern tall ships. A motley fleet of mostly Hollywood-built square riggers used to visit our small Port of Ilwaco here on the Lower Columbia, but the channel has silted and shoaled, and federal funds for dredging were cut, thwarting my stowaway plans :(

      daveS

      PS Pierre, Kite life should be closely comparable according to "realtive wind", crosswind or not. There is a greatly accelerated aging in higher relative wind, with even short load-peak events having a drastic effect. It pays to protect our sails by careful use.

      ----------------------------
      World UV Map-

      http://www.soda-is.com/maps/world_uv_ab.png



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