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