how much or how little efficiency from tossing and reeling in a sea anchor VS oars?

Discussion in 'Boat Design' started by Squidly-Diddly, Jun 11, 2015.

  1. Squidly-Diddly
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    Squidly-Diddly Senior Member

    or paddles or even propellers?

    I'm thinking once a sea anchor is deployed, reeling it in (or actually reeling yourself to the anchor) would be far more efficient than any of the conventional, more water trashing, modes of energy transfer.

    Plus, unlike oars, paddles or props, reeling a sea anchor would remain highly efficient over a wide range of energy rates/speeds.

    So now all you need to do is perfect a way to deploy the SA out in front of the boat, as well as design a slightly different anchor.

    Main two ways would be air-toss and micro-boat, or even micro-sub since a micro-boat might have trouble in even mild chop.

    On a ship you could have an runabout carry the SA out and when it pulls out all the line that yanks the SA off the stern and kills the motor. As the SA is hulled to the ship it pulls it out of the water to drain it a bit, then drops it back into the runabout which has been getting hauled back on same line just a bit after the SA.

    Sure it sounds a bit goofy, but compare that to the engineering and expense of standard ship engine and shaft and prop, VS a runabout, a line, a SA and big winch on deck, and you already got a runabout, line, SA and big winch on any ship.
     
  2. Village_Idiot
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    Village_Idiot Senior Member

    Why not just attach the SA to a long pole instead of a rope. Thrust it out deflated, retract it inflated. You could use multiple poles. I think there are little microorganisms that use this method of locomotion.

    If you need to stick with rope (for longer distances?), perhaps a cannon might be on order? Guess it would depend on your cheapest energy source (diesel vs gunpowder vs steam, etc.).
     
  3. Jamie Kennedy
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    Jamie Kennedy Senior Member

    You could pull yourself along with the transatlantic cable.
     
  4. Petros
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    Petros Senior Member

    a sea anchor is not a very efficent way to move a boat through water. they were not designed for that, but to generate drag. A good prop or oar design will have lift to drag ratios of perhaps 7 to 1 (think of the drag as the power input, and the lift as the forward thrust). round parachutes have L/d ratios of about 3 to 1 at best, they are just drag devices, not menant to converted power into forward motion.

    It might be possible to develop a device that you can pull through the water and actually generated thrust, but it would have to be much more complex than just a chute.

    At best using a sea anchor to move a boat would be only as an emergency means of moving the boat, and it will take a lot more work than a proper propulsion system. Oars or even kayak paddles would be a much more efficient use of your muscle power to get a boat to move than reeling in a chute.
     
  5. tom28571
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    tom28571 Senior Member

    No comment.
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    Sounds a bit hectic, doesn't it ? And the jerky progress......not to mention it isn't dolphin friendly. How about an underwater umbrella that closes when thrust forwards, but opens when retracted ? Reminds me of some of the devices Wile E Coyote uses on dry land.
     
  7. Jamie Kennedy
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    Jamie Kennedy Senior Member

    This might be handy...
    [​IMG]
     
  8. Petros
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    Petros Senior Member

    actually I was thinking of device like duct with two counter rotating fans in them, when you pull the assembly and force water through the duct, the two fans start rotating and generating thrust. Not sure if it would work the way I think, but it seems it should work okay. But it would be bulky and take up too much space when not in use.
     
  9. Squidly-Diddly
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    Squidly-Diddly Senior Member

    "You could pull yourself along with the transatlantic cable." There are shore-to-shore barge pulling cables, or were. One was featured across a river in the beginnings of "True Grit" w/John Wayne. IIRC that was a barge with two ropes and the ropes would be reeled on shore, possibly by draft animals after passing through a pulley (don't want the animals needed to deal with changing current vectors, just pulling in the same straight line they are used to).

    For longer distances, with today's tech, you could combine a traction cable with an alternating current power source. Float it a bit under the surface so it would miss wind driven driftwood and random vessels. Not an EE so I couldn't tell you exactly how you'd get "juice" from a cable in a marine environment to the boat being driven. So sort of "induction" I guess. With all this Crazy Money being through around by politicians this concept might at least be worth looking into for the Grant Money. :) A "Green" all electric ferry service that doesn't run on problematic huge special batteries.


    As far as "jerky", for anything but a one man boat you could have two set-ups, side by side. I don't think a taut cable being pulled on the port bow would bother resetting operations on the starboard since the bow would keep them separate.

    I see all the efficiency coming from when you are just hauling in the sea anchor, so you want the absolute max distance of deployment, miles not yards, so a pilot boat would be much better than a pole or even a cannon or catapult. Plus a pilot boat would require lots of reinforcement of the boat's structure.
     
  10. Jamie Kennedy
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    Jamie Kennedy Senior Member

    A long extension cord would not have to be as strong as a cable,
    so it could be much lighter in weight.

    [​IMG]
     
  11. SamSam
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    SamSam Senior Member

    There have been a few attempts to utilize water currents with underwater "sails"
    https://www.google.com/patents/US6694910

    [​IMG]

    There is that above and small river clamboats used to use small underwater sails also.

    But your idea doesn't seem feasible or practical. Sea anchors don't anchor, all they do is introduce drag to keep one end or the other of a boat faced upwind and/or to slow drift.

    If there was a rating system for efficiency for this scheme, a fixed post or a set anchor would rate 100 and a SA would probably rate .5 or something.

    To begin with, the energy required to overcome the inertia of a ship at rest would be horrendous, I imagine the size of a SA big enough would be several times larger than the ship itself.

    To move ships requires an engine roughly as big as your house. I don't see why the engine required to pull a ship along a cable hooked to a SA would be much smaller. The winch required would have to be bigger than any that has ever been made, just to handle all that horsepower. It would also have to pull in cable at 20-25 knots per hour to match the speed of a propeller. The size of the cable required to handle all that energy would be huge. No "runabout" is going to handle and deploy such a gigantic SA attached to a such a huge cable.

    As you say, it is a goofy idea and I think one that is totally impracticable, if not actually unworkable. It would be multiples less efficient than the propeller systems used now and so would cost multiples more to operate.
     
  12. nimblemotors
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    nimblemotors Senior Member

    I offered up this idea to a whitewater rafter a while back, who didn't want to carry a lot of weight to go upstream. The advantage going upstream is you can go slowly and not get pushed downstream and need a monster motor and enough water to keep prop working, just to stay still.
     
  13. SamSam
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    SamSam Senior Member

    Are you talking about the Wiley Coyote idea?
     
  14. DCockey
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    DCockey Senior Member

    Quick analysis:

    Uv - speed of vessel through water
    Ua - speed of anchor through water
    F - force between sea anchor and vessel
    Ada - drag area of sea anchor
    Adv - drag area of vessel
    rho - density of water

    F = 1/2 * rho * Ada * Ua^2

    F = 1/2 * rho * Adv * Uv^2

    Ua / Uv = (Adv / Ada)^0.5

    Rate of useful work done on vessel = F * Uv

    Rate of work done by vessel pulling in the sea anchor = F * (Uv + Ua)

    Efficiency = Uv / (Uv + Ua) = 1 / (1 + Ua / Uv)

    Efficiency = 1 / (1 + (Adv / Ada)^0.5)

    Efficiency increase as the drag area of the sea anchor increases. The drag areas will be speed dependent, not constant.
     

  15. gonzo
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    gonzo Senior Member

    A whaling harpoon would be the most efficient and exciting way to deploy the sea anchor.
     
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