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. whitepointer23

    whitepointer23 Previous Member

    what are you smoking. I want some.
  2. Squidly-Diddly
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    Squidly-Diddly Senior Member

    I'm thinking it would be more of a Sea Parachute, since Sea Anchors are only for directional stability and slowing drift. Would need a collapsing feature similar to how fish nets can be dumped by undoing whatever ties their ends shut, so when preparing to retrieve and reload you wouldn't be fighting all its captured water, just pulling fabric through water the "easy way" as it self-streamlines. Might not even carry the Sea Parachute on the runabout, maybe just drag it in collapsed streamlined form.
  3. fredrosse
    Joined: Jan 2005
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    fredrosse USACE Steam

    Sea Anchor

    Modern ship propulsion with screws achieves efficiency of well over 60%-80%, with propeller slip in the 20% vicinity. A very large sea anchor that would achieve similar slip while experiencing the thrust load of propulsion would require the same size engine to pull the ship toward the sea anchor.

    Taking an average screw propeller efficiency of 70%, then if the sea anchor was made infinitely large (in the limit, the same as a cable fixed on land), then, the ships engine could be 70% the size of the standard propeller ship's engine. However any real sized sea anchor would most probably have slip of 20-30%, so you would need the same size power plant on the ship with the sea anchor scheme.

    The added complication of getting the sea anchor in place far forward of the ship, inflating it like a parachute, then reeling it in, then extending it again and again is clearly not a practical proposition, even if it provided somewhat better propulsion efficiency, which it would almost certainly NOT be providing.
  4. gonzo
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    gonzo Senior Member

    Maybe so, but how about the excitement of launching it with a whaling harpoon like I suggested? No propeller will give you the same amount of fun. Plus, it can be used as a pirate deterrent.
  5. lucdekeyser
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    lucdekeyser Senior Member

    use a kite to drop the sea parachute in front ...
  6. nimblemotors
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    nimblemotors Senior Member

    If you are really talented and have the room, with nothing but a short cable as equipment one can throw an anchor quite a distance...


  7. Squidly-Diddly
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    Squidly-Diddly Senior Member

    You mean just the harpoon, or using the harpoon on a live whale and hoping he bolts in the right direction, towing the anchor behind him?

    But I'm really thinking the old rope driven barge across a water barrier or even a electrical cable driven ferry might work in certain spots (rush hour commute). Sort of like a cable sky-car, but with the water supporting the weight, and rope or elec. cable just providing propulsion.
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