Power to tow vs. power to propel

Discussion in 'Boat Design' started by misanthropicexplore, Jan 10, 2022.

  1. misanthropicexplore
    Joined: Apr 2018
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    Location: Upper middle Missouri River

    misanthropicexplore Junior Member

    Fantastic, thank you. Now I just have figure out how to put this information to use when there is no bank to walk on.
     
  2. DogCavalry
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    DogCavalry Soy Soylent Green: I can't believe it's not people

    Hip waders?
     
  3. portacruise
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    portacruise Senior Member

    (SF, Ca.) Cable Car type Towing ferry concept placed underwater near the bottom with Magnetic coupling /uncoupling as needed wouldn't block traffic?

    Mechanical pulling of shallow River barge flotillas using a steel cable winch located on the boat which powers forward, extends legs to a solid bottom, pulls, retracts legs, moves forward, repeats, like poling on a large scale, haha? Ps. Maybe the Winch boat does not have to anchor, if it has enough power to hold position, while the winch operates.

    Pps. The small scale kayak version involves using a drone to carry light weight leader line and an easily anchored pulley to an anchor position quite a distance Upstream, fill in the blanks, as you like, haha.
     
    Last edited: Jan 11, 2022
  4. messabout
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    messabout Senior Member

    This is the most fun thread in a long time.

    One thing not mentioned is the length of the tow rope. The longer the rope the less upward influence on the canoe. That trig is pretty apparent is it not?

    Having done upstream work both ways, I agree that it is easier to use a tow rope than to paddle or row if the upstream velocities are to be the same.
     
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  5. sharpii2
    Joined: May 2004
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    sharpii2 Senior Member

    Yes. Very much so.

    Before they had engines, British canal barge men had push-poles to use when foot-paths weren't available.

    One man could effective push a barge of maybe ten tons or more.

    I read of a case where one fellow pushed a barge up wind in a gale, and made good about 17 miles.

    That would be impossible with oars, or even a more efficient sculling oar.
     
  6. Tiny Turnip
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    Tiny Turnip Senior Member

    The record displacement for a ship pulled by a man on the dock is a rather astonishing 10300 tonnes. I presume in utterly windless conditions.
     
  7. fredrosse
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    fredrosse USACE Steam

    Keeping it quite simple, the propulsive efficiency of typical small boat propellers is in the vicinity of 50%, my sidewheeler, about the same, around 50%, so it is reasonable to assume typical oars or canoe paddles is around the same, say 50%.
    Efficiency of pulling a rope along a towpath is much closer to 100%, considering the rope pulling along the axis of the vessel. Some small correction may be appropriate for the rope angle being tilted from the axis of the keel, but efficiency still close to 100%.
    At the same speed, the rate of work input on the tow rope is about half what is needed with propeller, paddlewheel, oars, or canoe paddle.
    While these numbers are only approximate, rotating propeller efficiency is not commonly exceeding 60%, and I have never seen it as high as 70%

    For a small boat in displacement mode, (the hull speed less than 1.3 X SQRT(waterline length) ), the power required is linearly porportional to boat displacement, Therefore removing significant displacement weigh from the boat (the passenger providing the propulsion), and putting the propulsion power on the towpath, will further reduce the tow rope force.
     
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  8. gonzo
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    gonzo Senior Member

    There are canals in the southwest UK (Devon) that go through tunnels. They had workers that laid on the deck of the barges and walked them by pushing with their feet on the roof of the tunnel.
     
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  9. misanthropicexplore
    Joined: Apr 2018
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    Location: Upper middle Missouri River

    misanthropicexplore Junior Member

    I have this theory that all the important concepts an enthusiastic amateur could come up with probably wrapped up by the 1950's, that the future of any kind of meaningful improvement in anything that matters is large teams with big budgets. So, if I want to make any kind of a development it's got to be something trivial and obsolete...ie, all the good ideas are taken, and all that's left for me is stupid ideas. My stupid idea: something like a canoe anchor on an arrow, fired upstream with something like a bow fishing rig, and cranked in with foot pedals something like a pedalo. Sort of a human powered ferry for moving upstream. If nothing else it will disturb the hell out of the DNR.
     
  10. clmanges
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    clmanges Senior Member

    More topic drift, but a cable ferry in a strong enough current requires almost no external power at all. The boat is pushed off from the dock and then kept aligned at an angle to the current. The boat is pushed sideways to the current, and it crosses the river using the cable only as a guide to keep it moving perpendicular to the river. Most kayakers know the ferrying maneuver.
     
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  11. DogCavalry
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    DogCavalry Soy Soylent Green: I can't believe it's not people

    Not at all a topic drift, I think. But the ferry you describe is a sub type of the cable ferry, called a reaction ferry.
     
  12. DogCavalry
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    DogCavalry Soy Soylent Green: I can't believe it's not people

    It would take a very powerful engine, and a very jarge prop. And a lot more fuel than the shepard's pie and a pint of stout the fellow probably had for dinner afterwards.
     
  13. Tiny Turnip
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    Tiny Turnip Senior Member

    More topic drift. The development of 'fly boats' in the 1830's which travelled the canals at perhaps 10 mph, rather than the more usual 4 mph, is very interesting. It was a time when canal operators saw the threat of the advent of the railway and there was a strong incentive to go faster. These boats 'rose up on the bow wave' and produced little stern wave, and so didn't destroy the canal banks, (which is primarily why there are usually canal speed limits) It was claimed 'they could tow
    their maximum load of 22 tons at 10 mph even with a single horse'

    Their potential was discovered by accident by William Houston, and developed by John Scott Russell, who, in the course of his investigation, identified the soliton wave, now fundamental in a wide range of advanced scientific fields, neurology, nuclear physics, and it has even been suggested that they might hold the key to developing warp drive.

    So, @misanthropicexplore, you never know where your daft idea (which I like very much!) may lead!

    http://www.ma.hw.ac.uk/solitons/HISTORY_OF_EXPRESS_CANAL_BOATS.pdf
     
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  14. DogCavalry
    Joined: Sep 2019
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    DogCavalry Soy Soylent Green: I can't believe it's not people

    No kidding! And now researching details, I've just learned of chain boats!
    https://en.m.wikipedia.org/wiki/Chain_boat

    How cool is that?
     
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  15. Tiny Turnip
    Joined: Mar 2008
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    Tiny Turnip Senior Member

    Very cool! Never come across those before. We have a few chain ferries crossing rivers in the UK but I've never come across them as a means of propulsion up and down. Gotta love that Victorian ambition and confidence in their engineering!
     
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