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Sorry if this is the wrong exchange, if it is could you point me in the right direction that'd be awesome!

I have a bit of a problem locally that I think there could be a simple solution that we're not seeing. I'm part of the local volunteer group that cleans the river running through the town but a lot of rubbish is thrown in. We have litter pickers to get the close bits and what is in the weeds, nets to get the closer litter that floats on the surface, and hooks to try and get the heavy items out from under water, but that's where the problem is.

A lot of the items that get thrown in take a lot of energy and time to get out. They may include things like shopping trolleys (carts), we recently pulled out part of a car exhaust, car and bike tires, large metal or wooden poles, children's toys, chairs, wrought iron bench ends, and so much more! On the edge of the water there are thick reeds to promote biodiversity in the river, and wooden beams to support the bank. The hook very often gets caught on these and gets stuck, meaning we have to put our selves in danger to free it. I would happily jump in the water, because hey its just a bit of water, but the medical team that follows us has strongly advised us not to as there are a lot of rodents around and we could contract diseases such as weil's disease. The hook we use is attached to about 5 meters of rope which allows us to throw the hook in and attempt to catch the items, but if we miss then we just have to keep trying.

Below is a model cross section of the river that may help you visualise the area. Cross Section

I have thought of a potential solution to this that may help. We use one or two people either side of the river who hold a guide rope which the hook is freely attached to. Each side then has a rope attached to the rope so that they can pull the hook across the guide rope. The guide is lowered into the water to hook the item and then the attached ropes can be pulled to pull the item out. If the hook or item becomes trapped or free we would simply pull the hook in the other direction to reattach or free the hook again. A model of this is also attached below.

Solution

What are your thoughts on this? Could this be a valuable solution or am I just getting it completely wrong?

Thanks in advanced, Shaun.

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  • $\begingroup$ People are flexible and unstable and prone to fall down. I'd wonder whether the beams could be used to ride a "trolley car" on wheels, with the intent to provide a platform that is more stable? $\endgroup$
    – Jeffrey J Weimer
    Oct 1, 2018 at 15:30

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Instead of trying to hook floating debris from shore, I'd look into grabbing it from a canoe or other suitable watercraft.

Some items may be too large to lift into a canoe without risking capsizing during the process. Since you are willing to deploy two people, you could have one on shore and one in the canoe. The one in the canoe can attach the hook easily so that the one on shore can haul in the large item.

Small items are just lifted onto the canoe directly, and only need one person. A single person could do a sweep with a canoe, then come back to work with someone else on shore for the larger and more difficult items.

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  • $\begingroup$ Or a raft instead of canoe. Also makes for convenient storage of debris. Depends on how wide the river is though. $\endgroup$
    – ratchet freak
    Oct 3, 2018 at 9:59
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The main problem I see here is the force you need to pull anything up. If the margins are suficiently higher than the river that will be ok, but if the margins are at almost same level you will need to do a lot of force.

For example if θ is 10°, each person will need to do 2.9 times the force one would do alone if they were right above the object. And I am ignoring the weight of the rope which is probably not negligible specially if its get moist by dipping into the river.

If the river is narrow (like 15 feet) I think it will work but with 50 feet you will start to get tired real quick.

enter image description here

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  • $\begingroup$ This is correct. The closer it gets to horizontal the tension required gets ridiculously high as it does with a tightrope. Slack-rope walking, on the other hand, can be done between a couple of reasonably strong trees as θ will be quite high. $\endgroup$
    – Transistor
    Sep 2, 2019 at 18:14
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I would recommend something different: change the hook you are using. No matter how you are suspending it, at some point it'll foul. What would be ideal, then, is a grappling end with a locking hinge you can remotely release to change from, roughly, an L-shape to straight shape, thus freeing it from whatever is in the muck.

I took a quick look thru some camping and climbing sites, but their grappling hooks are all designed to open upon deployment, not release remotely. You may have to search deeper, or design your own "inverted" version.

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Seems reasonable.

In fact you probably don't need a guide rope if you just tie the hook into the centre of one long rope you can just take in slack on the appropriate side.

A further refinement would be to bring some lightweight shear legs or a gin pole. Either would provide a relatively lightweight and versatile way to allow you to lift rather than drag submerged objects. Both methods offer a reasonably efficient way to convert pulling force from ground level to a lifting force.

Essentially like a giant fishing rod or pole. Equally you have the option to use a pole with a rope fixed to the end as a large lever or with a pulley.

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