# Help me move a floating bridge 90 degrees w/o getting wet!

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1. Sep 7, 2016

### euphorik

Hello!

I was hoping someone here could help me solve a real world problem. So my university pool has something called a bulkhead, which is basically a bridge that floats above the water so that people can walk across the shorter dimension of the rectangular pool (50 meters long, 25 yards wide). You can see it clearly in this pic:
https://www.ohio.edu/recreation/aquatic/images/Banner-Aquatic_3.jpg
From time to time, the swim team will rearrange the pool lanes so that they are lengthwise and 50 meters long (they are 25 yards long in the pic) as they are during the Olympics.

In the process, to make room for the long lanes, the bulkhead needs to be moved along the long edge on the side with the windows. They have a good approach for rearranging the lanes, but the bulkhead always seems to take a while, especially when moving it back to the default position. Swimmers are not always around to help returning the pool to normal leaving pool staff to do it and one major problem is that someone has to get in the water to restore the pool to 25 yard lanes. There are lots of rings around the entire bulkhead and long rope is attached to one on the side opposite the windows; so switching to 50 meter lanes simply requires someone to walk across holding the rope and pull once on the side with windows.

But, as you can imagine, moving the bulkhead back so it acts as a divider for the pool is a little harder as it is not there to walk across anymore. The rope is not long enough to walk around the pool deck and people often trip over it when its on one end (sometimes falling in the water hilariously).

Longer rope is a possibility, but I really feel like there must be a more elegant solution to this. I've been thinking about different approaches, but can't seem to figure it out. Pulleys? Levers!? So, I turn to the physics forums in the hope that someone here can help me solve this. Thank you if you made it this far and apologies for the length of this post. Hopefully this is an interesting real world problem for someone!

2. Sep 7, 2016

### Staff: Mentor

We need more details.

Is it pivoted on one side?
Are there wheels?
Where does it move to?
What is the existing procedure?

3. Sep 7, 2016

### euphorik

It is free floating so it can be pivoted by only anchoring one side.
No wheels, it floats.
It moves to one of the long sides of the pool - figure A

The existing procedure to get from B to A is to detach long rope from anchor » (by detach I mean from the pool deck and not from the bulkhead), walk across, and pull slightly to the side to pivot around anchor « and place bulkhead flat against wall (anchor « only has short anchoring rope that doesn't reach across).
Getting from A back to B is what I need help with doing more efficiently. It would be really cool if there was a way to do it that didn't involve very long rope or getting in the water!

edit: fixed, formatting was off

Last edited: Sep 7, 2016
4. Sep 7, 2016

### CWatters

Longer rope. Store the rope properly when not in use.

5. Sep 7, 2016

### Orodruin

Staff Emeritus
If you have two people available you can try detaching both ends of the bulkhead with one person holding on to each end. Both people then walk in the same direction along the pool until they are in the two corners of one of the short sides and the bulkhead then lies along that short side. Both now walk at the same speed along the long side until they reach the point where the bulkhead should be attached.

Getting a longer rope and storing it properly (as pointed out in #4 -- it does not need to be the anchor rope, it can be any rope that can be attached to the bulkhead and later detached) is probably going to save you more time if possible though.

6. Sep 7, 2016

### A.T.

How would pulleys and levers be more "more elegant" than simply using a longer rope? "Elegant" in engineering usually means simple but effective.

7. Sep 7, 2016

### gmax137

make the bulkhead submersible (flood the hollow chambers). leave it in the default position, simply sink it to the bottom when you want 50 meter lanes. have an air hose attached, so you can blow out the chambers with a compressor to re-float the bulkhead.

otherwise, I'd go with the longer rope.

8. Sep 7, 2016

### JBA

It appears to me from your picture that you already have a number of "rope" candidates long enough for the job. Just use one of the 25 meter long floating lane separators shown in the picture

9. Sep 7, 2016

### BillTre

This is a variant of longer rope:
If there are ropes at both ends, untie both, secure the end near the final position side with enough extra rope to let you drag it around from the other end, pull the ropes in tight and re-secure.

10. Sep 7, 2016

### Ketch22

This is really a reply to the OP. More elegant in this case would be a longer rope as previously mentioned however it would go to a pulley on the opposite corner. The rope comes across the pool, through the pulley and returns to the pulling crew. In that way the force would be carried by the wall to which it was anchored and the people would fall away from the pool as opposed to into it.
If more force is needed Look up a three to one prussick arrangement like is commonly used in mountaineering or climbing. Also a " piggyback" rig could be used to increase force. I would be cautious of any force multiplication though as that bridge would have significant momentum and once you get it moving you need to stop it again in place.

11. Sep 7, 2016

### hsdrop

how tall is the roof of the swimming pool ??? is the bulkhead flexible (can it be rolled or coiled up)??does the bulkhead come all the way out of the water?? can it be moved (swung in the water) with one end attached??and does the pool have a safety pole that reaches at least have way across the with of the pool??? sorry for all the questions but i do have a couple of ideas that could work depending on how the pool and bulkhead are set up

Last edited: Sep 7, 2016
12. Sep 8, 2016

### bsheikho

Why not let it pivot on 1 of the anchors that its positioned in the 25m configuration. and only one side needs to have a long rope.

13. Sep 11, 2016

### rbelli1

The risk of the simple longer rope scenario is falling into a pool. If you are careful you don't fall. If OOPS! you fall in you get wet. Just don't let anyone that can't swim perform the maneuver. And take your cellphone etc. out of your pockets.

BoB

14. Sep 13, 2016

### votingmachine

I think the long rope makes the most sense.

But if I get the situation, there is a rectangle, fixed at one corner. It is easiest to move by pulling at the end furthest from the pivot point. But you can pull from any point. Say it s a 25 meter by 2 meter rectangle. You CAN grab the corner that is 2 meters from the pivot point and pull with a >2 meter rope. You will need to pull harder, as the leverage is different.

I suppose if you wanted, you could attach a bar that stuck out from that corner, and gain a bit of leverage. A pivoting bar would allow you to walk onto the bulkhead, attach the rope, swing out the bar, and then pull. I don't really have a sense of the water resistance, or mass, so my first try would be to just attach the 2 meter rope, and give a pull. If it then rotates ... well you can then decide if it is better or worse than other ways.

It will always be easier to walk out and attach to the 25 meter away corner, and pull that rope to rotate the bulkhead.

To get the rotation started, it might makes sense to push with a pole. Since the angle will change, you can start by pushing at the end, and then walk towards the pivot point with the pole, giving a push at intervals.

Between a push with a pole and an anchor point 2 meters with a pulling rpe, I would think you can rotate it without fear of getting wet.

15. Sep 13, 2016

### votingmachine

Another option is to stand on the bulkhead and "pole" it like a raft. You would probably need a pole with a rubber tip. But it seems simple enough to stand on the bulkhead and push the pool floor with the pole and make it swing around.

16. Sep 13, 2016

### axiom

2 anchor points 2 boat hooks and 2 lengths of rope...38ft and 30ft, given the walkway round the pool is approx 6ft wide.

Attach a 10 yard length of rope to the bottom left of the bulkhead and 12.5 yards to top right of bulkhead
Push the bulkhead approx 7.5 yards towards the middle of the pool.