View Full Version : scissor hoist examples

10-01-2011, 08:35 PM
A couple of books I've read have briefly mentioned a handy way of lifting heavy loads: two wooden beams are bolted together to form a long-legged X. I believe the load is carried from a line hanging from the junction.

The authors say that a single man can lift surprisingly heavy weights with this simple tool, but I guess they figure the reader is smarter than I am, because I can think of a few ways to lift weights with a tool like that, and none is the obvious one to use.

Does anyone here use a hoist like this? Do you push the legs together to lift things?

Peter Malcolm Jardine
10-01-2011, 08:45 PM
What do you want to lift? I have a lot of lifting devices... an engine crane, a small gantry with a chain fall, hydraulic jacks, scissor jacks, Jackall, all are suited to different purposes. You can construct lifting devices, but a lot of the stuff I have has been bought used or on sale, and quite cheaply. The issue is safety. I regularly move around loads of 1000 pounds, so I use the right equipment.

10-02-2011, 08:26 AM
I was interested in learning about the technology itself, so that I can realize it when I get into a situation where it would be appropriate.

But it had occurred to me that it might be helpful in serving as a helping hand if I could use this simple, cheap X hoist to hold up the end of a 200 pound hull while I flip it over from the other end, for instance.

10-02-2011, 08:45 AM
Some things are so simple, they plumb evade you. Be careful. If you take that X or V and lean it over, standing it up will lift it. Trouble is, if it goes too far, it'll fall the other way. Get a few friends to help you turn it over.

10-02-2011, 08:54 AM
I found the first place I saw mention of this tool: Colvin's Steel Boatbuilding. He called them "sheers".

"... It would be wise to make a sheers (Figure 61), which will make many of the jobs easier. This should be made of 4 x 4 material, with legs at least 16 feet long and of as clear a stock as possible, because the lifts required are such that one would not want them to fail."

Here's the diagram:


10-02-2011, 09:19 AM
I must admit, I'm puzzled by this as well.

10-02-2011, 09:39 AM
Levers. Basically a crude wagon jack. If one of the two pieces were considerably longer than the other it would work better, but at the prescribed length, that would be VERY long.

Mad Scientist
10-02-2011, 02:38 PM
The frame in Post #5 would be used to lift something straight up and set it down - such as lifting an inboard engine out of a boat.

But, then you need to move the boat out of the way and put the engine down. That's the tricky part. The frame needs to be supported so that it doen't fall over (it's obviously OK side-to-side) while the boat is moved. Definitely not a one-man job.


Ian McColgin
10-02-2011, 03:20 PM
Sheers are sheers - upright poles for lifting. Scissors, whether for cutting or for lifting are just conjoined second and third class levers - the part you lift, other end on the floor is a second class lever and where it applies its force is really the force on a third class lever with fulcrum underfoot on the floor and load at the other end. The advantage is that the point of lift on your load does not move in the horizontal, assuming the fulcrum of the third class is free to move a bit and the fulcrum of the second class stays put. It's a nice way to move something straight up or down.

Sheers take up verticle space while scissors take more horizontal space to set up.

jerry bark
10-02-2011, 04:56 PM
I think one perfect use for the "sheers" would be to hold the keg aloft while you wait for your rugby buddies to flip your hull. then once the hull is flipped it would be safe to lower the keg again. |;)

that said, if i had a small but heavy object to lift up just a bit I would not hesitate to use the sheers idea. a come along between the posts at the bottom and a small vertical lift would be easy. I would definitely brace "fore n aft" though.


Ian McColgin
10-02-2011, 05:28 PM
Sheers are great. I've stepped masts and removed engins by stepping the sheers on the gunnels and guying the top fore and aft. Sheers also make nice ends for monkey bridges or such things as the sort of arial tramway I made to get large propane tanks to a cabin up a difficult hill.

Wooden Boat Fittings
10-02-2011, 05:30 PM
The fore-and-aft bracing was carried out using lines -- topping-lift and martingale -- which also allowed the sheers to be tilted in either direction a small amount if necessary. But the lifting was done from the crutch at the top (where the legs join) by a block suspended there. Thus the sheerlegs themselves were in compression during lifting, and that's where their strength lay. (A relatively small cross-sectional member can take a lot of compression provided its slenderness ratio is such that it doesn't buckle.) Cross-bracing was sometimes used between the legs to reduce their effective buckling length -- ie reduce their slenderness ratio -- and hence increase their strength for a given size and length.


10-02-2011, 08:49 PM
Thanks much for the great responses.

Is it right that when adjusting the position of the sheers, the fulcrum is where the two legs meet the ground and that a guy pulls the crutch, but that when the load itself is lifted, it's by a line attached to the crutch, with mechanical advantage obtained not by the sheers themselves but by something else like a block and tackle?

I think maybe Ian McColgin's post is an unambiguous answer, but even after reviewing the lever classes, I'm having a little trouble translating it into a picture in my mind.

Ian McColgin
10-02-2011, 09:55 PM
Rather than worry about leverage, take some scissors and lay them on one edge so the handle of one blade and the tip of the other blade are on the table, then pull up on the handle in the air while you keep a finger of the other hand on the upper blade. The action will become clear then.

In practice, the closer the pivot between the two legs is to the load, the greater the leverage.

10-03-2011, 09:58 AM
Thanks, much. Yes, that's much easier to understand. I think that illustrates the "scissors" and horizontal case.

In the "sheers" or vertical case, is it different, with the load-bearing point E in the labeled diagram below lifted by pushing A towards B? I see there's a line between A and B that could be tightened.


Jay Greer
10-03-2011, 01:04 PM
Sheers were used at the Herreshoff Mfg. Co. for stepping masts and other lifing that was done at dockside before the turn of the last century.

10-04-2011, 03:00 PM
Yeah, based on re-reading Mike and others' posts, I'm thinking that sheers for vertical lifting rely on something external to the sheers for delivering a mechanical advantage, e.g., block and tackle. So the answer to my last post would be, "Um, no."

Mad Scientist
10-04-2011, 05:23 PM
In the examples I've seen, there was a block-and-tackle rig for the lifting, and the 'A-B' line was a safety line, because slippage of the legs might cause Jerry's beer keg (post #10) to fall and break. What a tragedy that would be!

Seems to me that trying to move the legs simultaneously would be impractical, which means that somebody will post an example any minute now! ;-)


Ian McColgin
10-04-2011, 06:38 PM
Yeah - There's a confusion here between sheers, which with a tackle may be used to lift things, with a scissors that is laid on its side to be used as a sort of compound lever.

10-04-2011, 08:08 PM
Yeah - There's a confusion here between sheers, which with a tackle may be used to lift things, with a scissors that is laid on its side to be used as a sort of compound lever.

I think you just put the last nail in the coffin of that confusion, sir.

Many thanks to all for the intelligent contributions to this thread!

Rational Root
10-05-2011, 02:22 AM
"moving heavy things"
jan adkins

About a tenner. Very short.

Shows how they did it without modern machines.

Great little book.