A mast and gaff hoist is a rigging arrangement that uses a vertical mast stepped over a shaft collar with an angled gaff spar pivoted at the masthead, working together as a controllable lifting boom for ore, timber, and equipment. You see this rig on small placer and hard-rock prospects — the Atlin and Cassiar shafts in northern British Columbia ran them well into the 1940s. The gaff swings the load clear of the shaft mouth so a bucket can be tipped onto a sorting platform without a full headframe. For a 2-man prospect, it lifts 200-400 lb loads from 30-60 ft depths cheaply.
Mast and Gaff Hoist Interactive Calculator
Vary load, gaff length, angle, and shaft depth to see hoist reach, lift travel, spar compression, and guy-rope pretension.
Equation Used
The calculator estimates the gaff end reach from simple trigonometry and the spar compression from the vertical load carried by an angled gaff. Lower angles give more reach but increase compression because sin(theta) is smaller.
- Static load with no shock factor.
- Gaff angle theta is measured above horizontal.
- Single vertical hoist line at the gaff end.
- Gaff compression is estimated from vertical load support by the angled spar.
- Guy-rope pretension follows the article guidance of roughly 10% of working load.
How the Mast and Gaff Hoist Actually Works
The rig works on two stacked principles. The mast — usually a 6 to 8 inch diameter peeled pole, stepped into a timber shoe at the shaft collar and stayed by 3 or 4 guy ropes — carries the vertical compression load. The gaff is a shorter spar, pivoted to the mast about two-thirds up by an iron jaw or a rope parrel, and held at angle by a peak halyard. The hoisting line runs from the windlass or hand-cranked drum at ground level, up through a sheave at the masthead, then out along the gaff to a sheave at the gaff end, and down to the ore bucket in the shaft. When you crank the drum, the bucket rises straight up the shaft. When it clears the collar, you slack the peak halyard and the gaff swings the load over a sorting platform or ore car.
Why build it this way instead of a single boom? Because a single fixed boom either sits over the shaft (and you can't dump the bucket without rigging a separate trolley) or sits over the dump zone (and you can't pull straight up a vertical shaft). The gaff gives you both — vertical lift first, then a controlled swing. The geometry depends on the gaff angle. At 30° above horizontal you get good reach but high compression in the gaff. At 60° you get short reach but lower spar loading. Most operators settle around 45°.
Get the tolerances wrong and the rig bites you. If the masthead sheave is offset more than about 2° from the line of pull, the rope walks off the sheave groove and jams between the cheek and the wheel. If the guy ropes aren't tensioned to roughly 10% of working load, the mast whips under shock loading when a stuck bucket breaks free, and you'll see the step shoe split along the grain. Failure modes are predictable — gaff jaw wear at the parrel, halyard chafe at the masthead, drum pawl skipping under load — all of them visible on inspection if you look weekly.
Key Components
- Mast: Vertical spar carrying the full lifting compression. Typically 6-8 inch peeled spruce or fir for hand-hoist rigs up to 1000 lb, stepped in an iron-shod timber shoe at the shaft collar. Length runs 18-30 ft above the collar so the bucket can clear when fully raised.
- Gaff Spar: Shorter angled spar pivoted to the mast at the parrel, swung by the peak halyard. Length is usually 60-70% of the mast length. Sets the horizontal reach over the dump zone — a 12 ft gaff at 45° gives roughly 8.5 ft of swing radius from the mast centreline.
- Parrel (Gaff Jaw): Iron-strapped wooden jaw or rope loop holding the gaff to the mast while letting it swing in the vertical plane. Working clearance must be 3-6 mm — tighter and it binds when the timber swells in wet weather, looser and the gaff slats sideways under load.
- Peak Halyard: Rope from the gaff end up to the masthead and down to a cleat at ground level. Adjusting it changes the gaff angle and therefore the dump radius. Sized at 5/8 inch manila or 1/2 inch wire rope for working loads up to 800 lb with a 5:1 safety factor.
- Masthead Sheave: Steel or hardwood sheave at the top of the mast that turns the hoist rope from horizontal pull to vertical pull down the shaft. Groove diameter must be at least 8× the rope diameter or the rope fatigues at the bend. Bearing is usually a bronze bushing — a sealed roller bearing is overkill for a hand-hoist duty cycle.
- Hoist Drum and Pawl: Hand-cranked drum, sometimes a horse-powered whim for larger rigs, with a ratchet pawl to hold the load when the operator releases the crank. Drum diameter typically 12-18 inches. Pawl tooth engagement must be at least 60% of full tooth depth or the pawl slips under shock load.
- Guy Ropes: 3 or 4 stays from the masthead to ground anchors at 45-60° from vertical. Tensioned to roughly 10% of working load so the mast stays plumb under shock without overloading the step. Manila for shorter service, wire rope for permanent installations.
Who Uses the Mast and Gaff Hoist
The mast and gaff hoist filled the gap between a simple windlass and a full headframe. Anywhere a small operation needed to lift loads from a vertical shaft and dump them clear of the collar without the capital cost of a steel headframe and steam hoist, this rig got the job done. You still find it on heritage sites and small-scale placer operations, and the geometry shows up unchanged on ship cargo derricks where it's known as the Stulcken or yard-and-stay rig.
- Small-scale placer mining: The shaft hoists at the Atlin and Cassiar gold camps in northern BC used mast-and-gaff rigs through the 1940s for 30-60 ft prospect shafts feeding hand-cobbing tables.
- Hard-rock prospecting: Cornish tin and copper prospects across the Penwith peninsula commonly used short mast hoists with a gaff for sinking exploration shafts before committing to a permanent whim or steam engine.
- Heritage mine restoration: The Britannia Mine Museum in Squamish BC and the Bralorne Pioneer Mine site both maintain functional mast-and-gaff demonstrations for shaft sinking interpretation.
- Salvage and recovery work: Used by the Yukon Mining Recorder's office for inspection and recovery of equipment from abandoned shafts where bringing in a mobile crane is impractical due to access.
- Marine cargo handling: The same kinematic principle drives the yard-and-stay derrick rig used on general cargo ships well into the 1980s, where two booms swing loads between hold and dock.
- Timber and pole construction: Pole barn and gin pole rigs used by rural contractors to set heavy beams use the same mast-plus-angled-spar geometry, often called a stiff-leg derrick when the gaff is a rigid strut rather than a halyard-trimmed spar.
The Formula Behind the Mast and Gaff Hoist
The number you actually need to size is the compression force in the gaff spar, because that's what governs spar diameter and parrel strength. The hoist rope tension equals the load weight (in a 1:1 reeving), but the gaff sees a much higher compression force depending on its angle. At the low end of the typical operating range — say 30° above horizontal — gaff compression runs roughly 2× the load weight, and the spar starts to feel marginal. At 45° (the design sweet spot for most rigs) compression sits around 1.4× the load. Push to 60° for short-reach work and compression drops to about 1.15× the load, but you've sacrificed dump reach. The formula below resolves the rope tensions at the gaff end into the spar-axis compression.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| Fgaff | Axial compression force in the gaff spar | N | lbf |
| W | Working load on the hoist rope (bucket plus ore) | N | lbf |
| θ | Angle of the gaff spar above horizontal | degrees | degrees |
Worked Example: Mast and Gaff Hoist in a heritage prospect shaft rebuild in the Klondike
A volunteer crew rebuilding a 1908-era prospect shaft on a tributary of the Indian River south of Dawson City is sizing the gaff spar for a mast-and-gaff hoist. The shaft is 45 ft deep, the bucket plus wet gravel weighs 350 lb, and they want to dump onto a sluice feed box about 7 ft from the shaft centreline. They have peeled spruce poles available in 4, 5, and 6 inch top diameters and need to choose the right one for the gaff.
Given
- W = 350 lbf
- θnominal = 45 degrees
- Mast height above collar = 20 ft
- Required dump reach = 7 ft
Solution
Step 1 — at the nominal 45° gaff angle, compute the compression in the spar:
That sets the design point. A 5 inch top-diameter spruce pole has a crushing strength along the grain of roughly 5,500 psi green and a cross-section of about 19.6 in², giving an ultimate axial capacity around 108,000 lbf — a comfortable safety factor of over 100 if buckling weren't a concern. But buckling is the real limit on a 12 ft slender spar, and Euler buckling for that pole sits around 4,200 lbf. Safety factor of 5 → working capacity 840 lbf. The 5 inch pole sits right at the line.
Step 2 — check the low-end of the operating range, 30°, which the crew might use for maximum dump reach:
At 30° the spar compression jumps to 1,306 lbf — that overruns the 5 inch pole's working capacity and the gaff would be visibly bowing under load. The crew would need the 6 inch pole, which gives roughly 8,700 lbf buckling capacity.
Step 3 — check the high-end, 60°, for short-reach operation:
At 60° spar compression drops to 606 lbf — the 4 inch pole would handle that with margin. But 60° gives only about 6 ft of dump reach from a 12 ft gaff, which falls short of the 7 ft sluice box. The crew is stuck with 45° as the design point and the 5 inch pole as the minimum.
Result
The gaff spar must carry 845 lbf of axial compression at the 45° design angle, and a 5 inch top-diameter spruce pole 12 ft long is the minimum acceptable choice. In practice this means the spar will feel firm but not stiff under load — you'll see a small flex at the gaff end of maybe 1-2 inches when the bucket lifts off, which is normal. Across the operating range, compression climbs from 606 lbf at 60° (lots of margin, short reach) through 845 lbf at 45° (the sweet spot) to 1,306 lbf at 30° (overruns a 5 inch pole — go to 6 inch). If the measured spar deflection exceeds 4 inches under nominal load, the most likely causes are: (1) the parrel jaw is allowing the gaff to rotate axially and the spar is loading off-axis, (2) the peak halyard is stretched beyond 3% (manila stretches under load and drops the gaff angle, raising compression), or (3) the masthead sheave bushing is worn and the rope angle at the masthead is biasing load into the gaff rather than down the mast.
Choosing the Mast and Gaff Hoist: Pros and Cons
The mast and gaff competes against three other small-scale shaft hoisting options: a plain windlass, a fixed gin pole, and a small steel headframe. Each has its slot. Pick wrong and you've either spent too much money or you can't dump the bucket without re-rigging.
| Property | Mast and Gaff Hoist | Plain Windlass | Fixed Gin Pole | Small Steel Headframe |
|---|---|---|---|---|
| Typical working load | 200-1500 lb | 100-400 lb | 500-2000 lb | 2000-10000 lb |
| Maximum practical shaft depth | 80 ft | 30 ft | 60 ft | 300+ ft |
| Dump-clear reach over collar | 6-10 ft (gaff swings) | 0 ft (must lift over by hand) | Fixed at build | Fixed dump chute |
| Setup cost (2024 USD, materials only) | $400-900 | $150-300 | $300-600 | $8,000-25,000 |
| Setup time on a virgin site | 1-2 days, 2 people | 4 hours, 2 people | 1 day, 2 people | 2-4 weeks |
| Hoist cycle time, 50 ft lift | 90-120 sec hand-cranked | 120-180 sec | 60-90 sec | 10-20 sec powered |
| Failure mode risk | Spar buckling, halyard chafe | Drum pawl slip | Single point of failure | Rope wear, low risk overall |
| Best application fit | Small prospect shafts needing dump-clear | Single-bucket sampling | Permanent small shaft | Production mining |
Frequently Asked Questions About Mast and Gaff Hoist
Because at θ = 0° the gaff is horizontal and the only thing resisting the downward pull of the rope at the gaff end is the vertical component of the peak halyard — and that component is also approaching zero. The denominator sin(θ) drives the compression to infinity.
In practice you can't actually run a gaff below about 25° on a working rig. The peak halyard tension goes through the roof, the parrel jaw lifts off the mast, and the spar starts to bow visibly. If you need more reach than 25° gives you, lengthen the gaff rather than dropping the angle.
Two things. First, sheave friction. A bronze-bushed wooden sheave eats 8-12% of the rope tension at each wrap, so by the time you've gone over the masthead sheave and the gaff sheave you're cranking against roughly 1.2× the load. Sealed roller sheaves cut that to 2-3% per wrap.
Second, rope angle at the drum. If the rope leaves the drum at more than about 2° off the perpendicular to the drum axis, you get fleet angle losses and the rope rides up on the drum flange. Move the masthead sheave so the rope feeds the drum perpendicular and the parasitic load drops.
Wire rope, but not for the strength reason most people assume. Manila stretches 2-4% under sustained load, and that stretch translates directly into gaff angle drop. A 30 ft halyard stretching 3% drops the gaff angle from 45° down to about 42° — small in degrees, but it raises spar compression by roughly 8% and shifts the dump reach by 4-5 inches.
Wire rope stretches about 0.3%. If the rig will sit loaded for hours at a time — sluicing, sorting, picking — wire rope keeps the geometry honest. For occasional use, manila is fine and easier on the hands.
Comes down to whether you need to vary the dump radius. The mast-and-gaff lets you trim the peak halyard and dump anywhere from minimum to maximum reach. The stiff-leg derrick has a rigid strut instead of a halyard-trimmed gaff, so the dump radius is fixed at build time but the rig is much stiffer and handles 2-3× the load on the same spar diameter.
Rule of thumb: if you have one fixed dump point (a sluice, an ore car track, a sorting bin) and the load runs above 800 lb, build a stiff-leg. If you have multiple dump zones or the layout might change, mast-and-gaff wins.
Two causes, both common. The first is timber compression at the step shoe — a green spruce mast can settle 1/2 to 3/4 inch into the shoe over the first month under cyclic loading, and that settlement slacks every guy on the shaft side because they're now anchored to a shorter mast. Re-tension after the first 50 hoist cycles.
The second is shaft-side ground movement. The collar timbers settle as you mine, and the mast follows. Check the plumb with a string-and-bob from the masthead weekly during active sinking. If you're seeing more than 2° of lean, reset the guys before the next shift.
Yes, but watch the line speed. Hand-cranked drums move the rope at 0.3-0.5 ft/sec, and the rig is sized for that duty. A typical 12V winch like a Warn 2500 runs the line at 4-8 ft/sec under light load — 10× faster — and the dynamic loading on the gaff jumps proportionally if the bucket snags and snaps free.
Two fixes. Either gear the winch down with a snatch block to halve line speed (and double available pull, which you don't need), or fit a load-limiter shear pin in the rope termination rated at 1.5× working load. The pin shears before the spar buckles. Don't skip this — a 350 lb bucket arresting at 6 ft/sec puts roughly 1,800 lbf shock load through the gaff, enough to fail a 5 inch spruce pole that handled the static load fine.
Around 80 ft for hand-cranking, 150 ft if you've got a horse whim or a small engine driving the drum. The limit isn't the rig — it's the rope mass and the cycle time. At 100 ft of lift with a 5/8 inch manila rope, you're cranking against 35 lb of rope weight on top of the bucket, and a single hoist cycle takes 4-5 minutes hand-cranked. Production drops below the cost of food for the crew.
Past that depth, switch to a counterweighted Koepe-style hoist or a proper headframe with a steel drum. The mast-and-gaff was always a small-prospect tool — if you're past 80 ft, the prospect has earned a real headframe.
References & Further Reading
- Wikipedia contributors. Derrick. Wikipedia
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