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Pulley System

GeorgeP's picture

Pulley System (post #191766)

GeorgeP on Tue, 07/27/2010 - 19:16
in

Hi, 
This really doesn't have anything to do with homebuilding but you guys have become my goto forum for anything mechnical.  I'm setting up a pulley system to hang a kayak from my garage ceiling.  I am using 4, two sheave blocks, two for the front and two for the back (to save my back).  At the back, i have the rope anchored to a point next to a block anchored to the ceiling. the rope goes down and through one side of the lower block, up through the same side of the upper block, down again to the other side of the lower block and then up to the remaining side of the upper block.  It then goes across the ceiling to the front  upper block, down, up, down and then up where the loose end goes through an eyebolt on the ceiling.  This is the front end of the kayak.  I hope the description is clear, it's not something I can deaw.  When I pull the rope the front end of the kayak raises very easily  but the back does not.  What I need to do is raise the front and then push the back up (which is also very easy) then raise the front some more etc etc until the boat is fully raised.  What I expected was for both ends to come up at the same time.   I may not stay with this system because of it's inefficiency but I'd like to know why it is not working as expected.  Can anyone help?

George

-A +A

It's not working because (post #191766, reply #1 of 12)

by DanH in reply to GeorgeP [original] on Tue, 07/27/2010 - 20:24

It's not working because pulley systems are haunted.  BTDT.

What you should do is run a rope/cable horizontally across the ceiling a goodly distance.  Tie the two ropes (front and back) to this first rope in a Y, arranged so that they will be pulled equally, and run each through a single pulley and down to one end of the kayak.  Tie the other end of the first rope to a lightweight hand-cranked boat trailer winch (either mounted on the ceiling, or on a wall, with a pulley to turn the corner), or tie the first rope to one end of one of your block-and-tackle rigs.


We are like tenant farmers chopping down the fence around our house for fuel when we should be using Nature's inexhaustible sources of energy -- sun, wind and tide. ... I'd put my money on the sun and solar energy. What a source of power! I hope we don't have to wait until oil and coal run out before we tackle that. --Thomas Edison

Boat winch = great idea. I'm (post #191766, reply #10 of 12)

by rdesigns in reply to DanH [original] on Fri, 07/30/2010 - 06:48

Boat winch = great idea. I'm gonna use it for my canoe. My current setup is pain to use--a single pulley system that lifts from the middle of the canoe and requires that you keep the thing level as you haul on the pulley rope.

BTW, boat wenches are handy, too. You can find them hanging around the docks.

  Dan, he is not pulling (post #191766, reply #2 of 12)

by Luka in reply to GeorgeP [original] on Tue, 07/27/2010 - 22:56

 

Dan, he is not pulling two ropes.

That's pretty much the problem.

 

George...

At the back, i have the rope anchored to a point next to a block anchored to the ceiling. the rope goes down and through one side of the lower block,

The end of the rope that you have anchored to a point next to the block there, should be pulled loose, and set up with the other rope, in the fashion that Dan described.

 

Basically, you have a system with two sub-systems. One sub-system for the front and one for the back.

(The 'sub-system' works by closing the distance between the two pulleys. The boat just comes along for the ride.)

By pulling only on the one end of the rope, you 'close' that system first.

If you pull on both ends of the rope, equally, you should be closing both systems simultaneously.

 

Leaving it set up like it is... Once you have pulled the front of the boat to the ceiling, if the ropes and pulleys are not binding anywhere, then continuing to pull on that first rope, -will- pull the back system closed at that time. Bringing the back of the boat along for the ride.


The best bet is to anchor the rope ON the bottom pulley. (With the boat then hanging off of the bottom of the pulley.) Then run the rope up through one side of a double pulley, (or 'block"), then back down through the bottom pulley. Then back up through the other half of the double pulley... And then out to where you pull on it.

Do this at each end of the boat. Separate ropes... And then follow Dan's instructions. Tie them together, and pull on them equally.

.

It's a small world. Until you have to walk home...

Dan, he is not pulling two (post #191766, reply #3 of 12)

by DanH in reply to Luka [original] on Wed, 07/28/2010 - 05:13

Dan, he is not pulling two ropes.

Right.  The problem is with friction -- friction is much lower in whichever pulley set is moving, so the other one never moves.  And since the rope will always be moving through the set of pulleys on the "bitter" end of the rope, that set will (almost) always win.


We are like tenant farmers chopping down the fence around our house for fuel when we should be using Nature's inexhaustible sources of energy -- sun, wind and tide. ... I'd put my money on the sun and solar energy. What a source of power! I hope we don't have to wait until oil and coal run out before we tackle that. --Thomas Edison

Thanks.  I realized what was (post #191766, reply #4 of 12)

by GeorgeP in reply to GeorgeP [original] on Wed, 07/28/2010 - 05:39

Thanks.  I realized what was happening as I was tryng to get to sleep last night.  I had it set up with two ropes but wanted to see if I could do it with one.  I saw a setup online that used one rope but they used a single pulley on the back end not a block.  I'll just go back to the two ropes.


George

http://www.target.com/gp/deta (post #191766, reply #5 of 12)

by cussnu2 in reply to GeorgeP [original] on Wed, 07/28/2010 - 08:52

http://www.target.com/gp/detail.html/187-2190429-1403001?asin=B000ME0TW8&AFID=Froogle_df&LNM=|B000ME0TW8&CPNG=sports&ref=tgt_adv_XSG10001

 

What you are trying to do is no different from this bicycle hoist which is sold all over the place.  You could opt to go for one of these or rig yours the same as this.

I was thinking the same, I (post #191766, reply #6 of 12)

by xxPaulCPxx in reply to cussnu2 [original] on Wed, 07/28/2010 - 10:33

I was thinking the same, I use my bike hoist to hold up all sorts of things in the garage.  If only one side lifts, it just takes a sec to push the other side back up so it matches.

YAY!  I love WYSISYG editing!  And Spellcheck!

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Thing is, a kayak's a bit (post #191766, reply #7 of 12)

by DanH in reply to xxPaulCPxx [original] on Wed, 07/28/2010 - 18:09

Thing is, a kayak's a bit larger/longer than a bike, and it's a trick to hold the rope and run back and forth between the two ends of the boat.

Of course, a good cam cleat would help here.

I've done the rope thing with a small sailboat, and with a model RR layout, and tried several different schemes.  By far the best is the Y rope scheme.


We are like tenant farmers chopping down the fence around our house for fuel when we should be using Nature's inexhaustible sources of energy -- sun, wind and tide. ... I'd put my money on the sun and solar energy. What a source of power! I hope we don't have to wait until oil and coal run out before we tackle that. --Thomas Edison

On a bike hoist, you are (post #191766, reply #8 of 12)

by xxPaulCPxx in reply to DanH [original] on Thu, 07/29/2010 - 10:33

On a bike hoist, you are under the bike as you lift it... and you only need to be on one side if you need to adjust it up or down.

Plus, you can get it nearly flat with the ceiling - something you can't do with a Y.

YAY!  I love WYSISYG editing!  And Spellcheck!

____________________________________________________

Why can't you get it flat to (post #191766, reply #9 of 12)

by DanH in reply to xxPaulCPxx [original] on Thu, 07/29/2010 - 17:26

Why can't you get it flat to the ceiling with a Y?


We are like tenant farmers chopping down the fence around our house for fuel when we should be using Nature's inexhaustible sources of energy -- sun, wind and tide. ... I'd put my money on the sun and solar energy. What a source of power! I hope we don't have to wait until oil and coal run out before we tackle that. --Thomas Edison

Maybe I'm not imagining it (post #191766, reply #11 of 12)

by xxPaulCPxx in reply to DanH [original] on Fri, 07/30/2010 - 10:33

Maybe I'm not imagining it right, but wouldn't the pulley be stopped at the yolk of the Y where the single rope split into two?

YAY!  I love WYSISYG editing!  And Spellcheck!

____________________________________________________

Put two pulleys over the ends (post #191766, reply #12 of 12)

by DanH in reply to xxPaulCPxx [original] on Fri, 07/30/2010 - 11:11

Put two pulleys over the ends of the boat.  Ropes from there join in a Y to a rope that runs along the ceiling (eg, to an appropriate wall) to a 3rd pulley that leads down to the cleat/winch (or one can mount the winch on the ceiling and dispense with the 3rd pulley).  You need to have enough space between the pulleys for the length of the rope that will be moving -- eg, for an 8 foot lift you want 10-12 feet horizontal, at least.


We are like tenant farmers chopping down the fence around our house for fuel when we should be using Nature's inexhaustible sources of energy -- sun, wind and tide. ... I'd put my money on the sun and solar energy. What a source of power! I hope we don't have to wait until oil and coal run out before we tackle that. --Thomas Edison