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This came to me when I was watching cargo ships going up and down the Mekong river, of course going upstream against the strong current uses a crapload more energy than going downstream (which effectively uses none). I thought about the old towpaths in the UK where a horse walking next to the canal pulls
boats up the canal.
Basically the "crawler" is a heavy tracked vehicle which rests on the riverbed facing upstream. Its entire body is a giant turbine which drives the tracks through a reducing gearbox. It has to be too heavy to get swept away and stable enough that it can't tip over. It can then pull a boat upstream, quite slowly but it's free! It could be remotely steered by cables or self-steering using vanes that keep it facing into the current. When the boat reaches its destination the crawler is lifted aboard for the trip back downstream.
A variation on this, if the riverbed is too soft or uneven, install a chain or toothed rail along the route, the "crawler" is a machine adapted to pull itself along the chain/rail again using a water-driven turbine. But then you have the cost of installing this infrastructure.
Shuttlepig
http://www.dpt.co.u...nology/freeflow.php
[cpmcc, Nov 16 2008]
[link]
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Just how slowly does it go? I'll bun the idea, since it's pretty cool, and might have some limited applications. But I think I'm gonna miss that horse. |
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Could the boats going down be used ?
They could put out sea anchors for greater current capture . Five riverside turbines to the one crawler . |
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The turbine needs to resist all the energy of the water to move forward. In a perfect machine, 100% of the energy will be returned. That gets you nowhere. |
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Ah! I figured it out. The turbine is lowered into the water, and the spiked wheels lock into an above-water track. Energy is collected. Then the turbine lifts out of the water and the crawler inches forward until the battery dies, at which the turbine drops back into water, and the cycle repeats. In this case the lighter the vehicle the better. |
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An improvement:
Turbine is on the bottom of the ship. There is no fixed interface between ship, ship-based apparatus, and the riverbottom. Riverbottoms are mucky and are often mainatined very deep when used by seagoing freighters. Plus crawdads and stuff live there. |
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Railroad is alongside the river. Crawler is mounted on dry rails and powered by undership turbine. It pulls ship along. It can be less heavy and has a better purchase. Land-based system does not get destroyed by the river as quickly. |
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Is not the impulse against the blades of the turbine going to force the boat downstream? The turbine needs to be Fixed in Place. Hense, I think mylodon's second design is most appropriate, given that heavy anchors are used to stabilize the boat during charges. |
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Hi mylodon, I'm 99% sure the crawler could move forward against the current. Because sailboats can sail almost directly into the wind, and they are not very efficient machines. The crawler would not move upstream anywhere near as fast as the river flows - maybe a tenth of the speed or less. Which is fine for lots of non-time-critical cargo. |
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The water resistance is low because the cross-section of the crawler is as small as possible, except for the turbine inlet which is as large as possible. |
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I really like the claw idea. The tracks could have claws on them for extra grip on cruddy river beds. |
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It doesn't have to be *that* heavy overall: a submarine type thing with tracks and ballast. |
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A sailboat's keel gets a "grip" on the relatively stationary water, and allows extraction of energy from the motion of the passing air. |
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There are a number of analogous ways you might get a "grip" on a riverbottom / shore / other boat / alligator to hold a bit while the river rushes past your turbines / props / paddlewheels / clockwork-oar mechanism... |
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[mylodon], I've never quite gotten my head around whether you're right or not. The crux of my confusion is this: With a sufficiently large gear ratio, could you not produce enough force to move forwards? I'm not sure. It doesn't quite make sense that one cannot do it continuously (gearbox) but can do it in discrete steps (absorb power, then expend it). |
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How about this: The power absorbed is based on the force on the turbine blades and the velocity of the flow relative to the blades. The power expended is based on the force on the whole vehicle and the velocity of the vehicle relative to the river bed. For a given power extraction, there is therefore a maximum, perhaps low forward speed possible. Does that stack up, or am I talking nonsense? |
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Shuttlepig baked it for pipes. [link] |
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[mylodon] why not just turn the blades to align with current when in 'move' mode? |
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as for [ds] comment, someone more intelligent than me needs to comment. |
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It'd be a whole lot faster if it moved above the water. |
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Plus you'd have less pink river dolphins fouling up the turbines. |
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