A shears with winch or tackle block is a two-legged A-frame derrick — two spars lashed or pinned at the top — that hoists a load through a sheave at the apex, with the line led down to a winch or block and tackle for mechanical advantage. A modest 4-part tackle multiplies a 500 lb winch pull into roughly 1,800 lb of usable lift after friction losses. Riggers use shears to set heavy loads where a single gin pole can't take side load, like raising stone columns, ship masts, or steel pylons in tight sites.
How the Shears with Winch or Tackle Block Actually Works
The shears is the simplest two-legged lifting rig you'll find on a job site. Two timber or steel spars meet at an apex, lashed or pinned together, with the feet spread on the ground at roughly 1/3 to 1/2 the leg length. A back stay runs from the apex down to an anchor behind the rig, and a fore guy controls forward lean. The load hangs from a sheave or hook at the apex, and the fall line — the rope you actually pull — runs down through the tackle block to a winch, capstan, or hand crab.
The geometry matters more than people think. The apex angle between the legs sits between 20° and 40° in most builds. Open it wider and the legs spread further apart on the ground, which gives you a stable base but cuts the headroom you can lift to. Close it tighter and you gain height, but the compressive load in each leg climbs fast — at 15° apex angle the leg load runs nearly 4× the load weight, and a green spar will buckle before you ever see the load lift clean. The back stay does almost all of the work resisting the overturning moment when the rig is leaned forward to plumb the load over a foundation. If that anchor pulls — and it does, on soft ground, when riggers underestimate the pull — the whole shears comes down forward onto the load.
The tackle block is what turns a small winch into a serious lifter. A 4-part tackle uses 4 rope parts between a fixed and a moving block, so the load on each part is roughly 1/4 of the total load. Real efficiency runs 85-90% per sheave because of rope stiffness and bearing friction, so a 4-part tackle delivers closer to 3.4× mechanical advantage rather than the textbook 4×. If you notice the fall line jumping or the load drifting sideways during lift, the most common cause is a twisted rope reeving or a sheave that's seized — both will spike the line tension and can part the rope at the deadeye.
Key Components
- Shear legs (spars): Two compression members — solid Douglas fir, steel pipe, or lattice tube — that carry the load down to the ground. Sized so the slenderness ratio L/r stays under 120 for timber and under 150 for steel, otherwise buckling governs before crushing.
- Apex lashing or pin joint: Holds the two leg tops together at a fixed angle. A traditional rope lashing uses 8-12 turns of 3/4 in manila with frapping turns between the legs. A modern build uses a steel gusset plate with a 1 in pinned clevis rated for the full apex compression.
- Head sheave (apex block): Single sheave or snatch block hung at the apex through which the hoist line runs. Sheave diameter must be at least 16× the rope diameter for wire rope — drop below that ratio and rope fatigue life cuts by half.
- Tackle block (purchase): Multi-sheave block pair that gives mechanical advantage. 2-part, 4-part, and 6-part are the common purchases. Each added part roughly halves the line pull but cuts efficiency by another 10-15% per sheave, so 6-part rarely beats 4-part in practice.
- Back stay: Tension line from apex to a rear anchor — deadman, rock pin, or building tie. Carries the horizontal reaction from the leaned rig. Must be sized for at least 1.5× the load weight at typical 30° lean angles.
- Fore guy: Forward-running line that controls how far the apex leans toward the load. Used to swing the load in or out and to lower it onto a foundation.
- Winch or hand crab: The pulling end of the fall line. Hand winches run 500-2000 lb single-line pull, powered drum winches run 5,000-50,000 lb. The winch must be anchored to take the full fall-line tension, not just bolted to a light frame.
Real-World Applications of the Shears with Winch or Tackle Block
Shears rigs show up wherever a fixed crane can't reach and a mobile crane can't fit. Heritage construction, shipyards, antenna and pole work, and remote infrastructure all still use shears because the rig packs flat, assembles with two riggers, and lifts loads that would otherwise need a 60-tonne mobile.
- Heritage masonry: A stonemason crew at the Salisbury Cathedral works yard uses a 9 m oak shears with a 4-part manila tackle to set 1,800 lb Chilmark stone replacement quoins onto the third-tier buttresses where a truck crane can't get past the cloister wall.
- Shipbuilding and yard work: Wooden boat builders at the Rockport Marine yard in Maine raise 40 ft Sitka spruce masts onto schooner hulls using a steel-pipe shears anchored to the dock, with a Lug-All 3,000 lb hand winch driving a 4-part purchase.
- Telecommunications: Tower crews from Sabre Industries use a portable aluminium shears to top-mount 600 lb microwave dishes and side-arm assemblies on lattice towers above the climbable section, where a gin pole would need a separate base mount.
- Hydroelectric maintenance: BC Hydro penstock crews use a shears anchored to the surge tank deck to extract 4,000 lb butterfly valve stems for inspection — the rig folds flat and rides up the access tram in two pieces.
- Oil and gas well servicing: Workover crews on stripper wells in the Permian Basin still rig a small shears over the wellhead to pull rod strings and tubing when a service rig isn't economic for a 500 ft well.
- Bridge restoration: Heritage bridge crews working on covered timber bridges in Vermont use timber shears to lift replacement chord members into place where the deck won't carry a crane outrigger load.
The Formula Behind the Shears with Winch or Tackle Block
The two numbers that decide whether a shears build will work are the line pull required at the winch and the compression load down each leg. The line pull tells you which winch to specify — at the low end of typical site loads, say 500 lb, a hand crab handles it. At the high end, 5,000 lb and above, you need a powered drum winch with a brake. The leg compression tells you whether your spars survive — at a wide 40° apex angle each leg sees roughly 0.55× the load, comfortable for a 6 in timber. Close that apex to 15° to gain headroom and each leg sees nearly 1.9× the load, which buckles a green timber long before the lift completes. The sweet spot sits around 25-30° apex angle for most field rigs.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| Fline | Line pull required at the winch (fall line tension) | N | lbf |
| W | Load weight at the hook | N | lbf |
| n | Number of rope parts in the tackle (purchase parts) | dimensionless | dimensionless |
| η | Per-sheave efficiency (typical 0.90 for plain bearing, 0.96 for roller bearing) | dimensionless | dimensionless |
| Fleg | Compression load in each shear leg | N | lbf |
| θ | Apex angle between the two legs | degrees | degrees |
Worked Example: Shears with Winch or Tackle Block in a mining headframe pulley change-out
A small underground gold mine near Timmins Ontario needs to swap out the 2,400 lb head sheave on a 1940s-era timber headframe over a 180 m shaft. The hoist house is too close to bring in a mobile crane, and the headframe deck won't take a spider crane's outrigger pad pressure. The maintenance crew rigs a 7 m steel-pipe shears on the deck above the sheave, using a 4-part wire-rope tackle to a 1,500 lb-rated electric winch bolted to the deck framing. They set the apex angle at 30°. Calculate the required line pull and check the leg compression.
Given
- W = 2400 lbf
- n = 4 parts
- η = 0.92 per sheave
- θ = 30 degrees
Solution
Step 1 — at the nominal 4-part tackle, compute the cumulative efficiency factor:
Step 2 — line pull at the winch for the nominal 4-part purchase:
Step 3 — leg compression at 30° apex angle:
At the low end of the typical purchase range, a 2-part tackle, the line pull jumps to Fline = 2400 / (2 × 0.922) = 1418 lbf — that overruns the 1,500 lb winch with no margin and a stalling motor will trip the breaker on the lift. At the high end, a 6-part tackle drops the line pull to Fline = 2400 / (6 × 0.926) = 645 lbf — easier on the winch, but you've added two more sheaves to reeve, the fall line moves 6 ft for every 1 ft the load lifts, and total lift time triples. The 4-part build is the sweet spot here.
For the legs, at a wide 45° apex the compression drops to 1,300 lbf — safe but the rig stands taller and narrower. Close to 15° apex and each leg jumps to 2,318 lbf, which is a 60% increase over the 30° case for only an extra 0.5 m of headroom. Stay near 30°.
Result
The crew needs roughly 840 lbf line pull at the winch and the legs see about 1,240 lbf compression each — well inside the 1,500 lb winch rating and easily handled by a 4 in schedule-40 steel pipe. At 840 lbf, the winch motor sits at about 56% of rated load and lifts at full rated line speed, which feels like a steady controllable haul rather than the labouring stop-start of a stalling winch. Compare against 1,420 lbf for a 2-part purchase — winch overruns and trips — versus 645 lbf for a 6-part — comfortable but slow and over-reeved. If your measured line pull comes in 15-20% above the 840 lbf prediction, check first for a fouled tackle reeving where rope twist is binding the sheaves, second for a seized sheave bearing on the moving block (run a free-spin check before rigging), and third for the fall line angle leaving the head sheave — anything beyond 5° off-axis adds significant side-load friction and chews the rope shoulder.
When to Use a Shears with Winch or Tackle Block and When Not To
A shears isn't the only way to lift a heavy load on a constrained site. Riggers pick between a shears, a single gin pole, and a small mobile crane based on load weight, headroom, anchor availability, and how often the rig moves. Each has a clear lane.
| Property | Shears with tackle | Single gin pole | Mini mobile crane |
|---|---|---|---|
| Typical load capacity | 500-20,000 lb | 200-5,000 lb | 2,000-100,000 lb |
| Setup time (2-person crew) | 2-4 hours | 30-60 minutes | 15-30 minutes |
| Side-load tolerance | Good — two legs share lateral load | Poor — single pole, all load axial | Excellent — designed for slewing |
| Required anchor points | 1 back stay + 1 fore guy minimum | 3-4 guy lines around 360° | None — outriggers only |
| Lift height limit | Spar length minus apex losses (~85%) | Full pole length | Boom length, often 15-30 m |
| Cost (rig only) | $500-$5,000 for timber/pipe build | $300-$2,000 for a single spar | $80,000+ purchase, $400-$1,200/day rental |
| Best application fit | Heavy lifts in tight sites with rear anchor available | Vertical lifts on towers, antennas, masts | Open sites with road access |
| Skill level required | Experienced rigger — geometry matters | Moderate — guy tensioning is the trick | Certified crane operator |
Frequently Asked Questions About Shears with Winch or Tackle Block
The back stay is stretching under tension and the rig is hunting for equilibrium. As soon as the load lifts off, the full overturning moment transfers to the back stay, and any rope or wire elongation lets the apex rotate forward. Manila stretches 8-12% at working load, polyester 3-5%, and 6×19 wire rope about 0.5-1%.
The fix is either a back stay made of wire rope rather than fibre rope, or pre-tensioning the back stay before the lift starts so the rig is already at its loaded position when the hook takes weight. If the lean keeps progressing after the load is fully off the ground, your anchor is dragging — stop the lift and re-set the deadman.
Two things drive the call: lift speed and reeving friction. A 6-part tackle moves the fall line 6 feet for every 1 foot of lift — three times the rope haul of a 2-part — so on a long lift the winch drum capacity becomes the limit, not the line pull.
The second issue is cumulative sheave efficiency. Each sheave loses 8-12% of the input force, so a 6-part tackle delivers maybe 4.5× actual MA versus the textbook 6×. By the time you've added the extra reeving complexity and slowed the lift, you've often given back the advantage. Pick the lowest part count that keeps line pull under 75% of winch rated capacity.
Tighter apex angles give more headroom but spike the leg compression non-linearly. Going from 30° to 20° apex gains you about 4% extra height on a 7 m leg but adds 50% to the leg compression. Below 15° you're approaching the buckling limit on most field-grade timber, and the rig becomes laterally unstable — a small side load can collapse it.
The practical floor is 20° apex angle on engineered steel pipe, 25° on solid timber. If you genuinely need more headroom, switch rigs — a single gin pole gives you the full spar length vertically, at the cost of needing four guy lines instead of two anchors.
No. Winch ratings are first-layer drum ratings, and line pull drops as rope wraps build up on the drum — typically 10-15% per layer. By the third layer you've lost 30% of your rated pull, and a marginal lift will stall mid-haul.
Add to that the possibility of a sticking sheave, a fouled reeve, or a load that turns out heavier than the drawing said, and you want at least 25% margin between calculated line pull and rated first-layer winch capacity. If you're at 100%, drop down a tackle part — go from 4-part to 6-part — or step up the winch.
Pre-tension the back stay to roughly 1.5× the calculated working tension using the winch and a snatch block, hold it for 5 minutes, and watch the anchor for movement. On a deadman, any visible soil heave on the up-slope side means the anchor is creeping. On a rock pin, watch for spalling around the pin hole.
The number you're loading the anchor to depends on your apex angle and the load — at 30° forward lean with a 2,400 lb load, the back stay sees about 1,200 lbf working tension, so you'd proof-test to 1,800 lbf. Riggers who skip this step are the ones whose rigs end up across the load.
Almost always a sheave-to-rope diameter mismatch. The rule for 6×19 wire rope is sheave tread diameter at least 16× rope diameter, and 30× is preferred for long service. Drop below 16× and the rope bends into the sheave too tightly, fatiguing the outer wires on every pass over the sheave.
Check the actual sheave tread diameter against your rope size — a 1/2 in rope wants an 8 in sheave minimum. If you're using a snatch block scrounged from another job, measure it. The other common cause is a sheave groove worn flat, which lets the rope flatten and crush — if you can lay a straight edge across the groove and not see a clear U, replace the sheave.
Only within a narrow envelope. A shears resists side load by spreading the foot of one leg further out and lifting the foot of the other — once the unloaded leg lifts off the ground, the rig hinges and falls. Practical side swing is maybe ±10° from the plane of the legs before the unloaded foot starts to lift.
If you need to land a load any distance off the lift line, plan the foot positions before the lift so the load lands inside the leg envelope, or swing it on the fore guy by walking the apex forward while keeping the back stay tensioned. For genuine slewing capability, the shears is the wrong rig — use a swing derrick or a small crane.
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