Ramp Haulage: Winch Capacity and Anchor Limits
A cadet is asked to move a 260 kg crated pump up a straight ramp into a plant room. The ramp rises at 15 degrees to the horizontal and is 18 m long along the slope. The crate sits on a steel skid, and the coefficient of friction between skid and ramp is 0.25. A hand-operated winch is bolted down at the top of the ramp; its rated line pull is 2.5 kN and it hauls at a steady 0.4 m/s. The winch motor is rated 750 W. The winch is anchored through a 12 mm forged eyebolt with a stated working load of 3.0 kN, resin-fixed into a concrete slab whose thickness and edge distance are not recorded anywhere on site. The rope runs parallel to the ramp. Take g as 9.81 m/s^2. Before the lift starts, the cadet must say whether the winch is adequate, how long the pull will take, and which component really sets the limit on the job.
1. Calculate the force needed to start the crate moving up the 15 degree ramp and compare it with the winch rating. Is the winch adequate?
Read the worked answer
Weight: W = mg = 260 x 9.81 = 2550.6 N.
Components:
- Down-slope weight: W sin15 = 2550.6 x 0.2588 = 660.1 N
- Normal force: W cos15 = 2550.6 x 0.9659 = 2463.6 N
- Friction to start (static, skid on steel): 0.25 x 2463.6 = 615.9 N
- Total required pull: 660.1 + 615.9 = 1276 N, about 1.28 kN
Margin: 2500 / 1276 = 1.96, so the winch will do the job on paper.
Judgement points that must be raised:
- A factor of 1.96 is thin for a hand-operated pull. Skewing on the ramp raises friction, a wheel or skid corner catching a ramp joint applies a shock load, and the rated pull is normally quoted at a particular rope layer on the drum, not at every layer.
- The 1276 N is the starting figure; once moving, friction drops slightly and the pull falls, so the motor is not the concern - the anchor and the rope condition are.
- Recommend confirming the drum layer rating and adding a snatch block (halving the line pull) if any of these conditions cannot be confirmed.
2. How long will the 18 m pull take, and how much power is demanded from the 750 W motor? Comment on the margin.
Read the worked answer
Time: t = distance / speed = 18 / 0.4 = 45 s.
Work done against the resisting force: 1276 x 18 = 22.97 kJ (about 23 kJ).
Power at the load: P = F v = 1276 x 0.4 = 510 W.
Motor margin: 510 W is 68% of the 750 W nameplate. Allowing roughly 78% winch/gearbox efficiency, the electrical or manual input needed is about 510 / 0.78 = 654 W, which is 87% of rating.
The winch will complete the pull, but the margin is only about 13%. That matters because:
- Nameplate ratings are usually continuous, and starting torque/current is higher than running values.
- A skew or a jam on the ramp drives the demand straight past 750 W.
- The 45 s figure assumes no stops and a constant 0.4 m/s, which is optimistic on a hand winch.
Conclusion: power is acceptable for a clean, straight pull; a snatch block (which halves both line pull and power) would make the job comfortably inside rating.
3. Between the winch, the eyebolt and the concrete, which element actually limits this job, and what should the cadet do before authorising the lift?
Read the worked answer
Compare the numbers we have:
- Winch: 2500 / 1276 = 1.96 on required pull.
- Eyebolt: 3000 / 1276 = 2.35 on the same pull.
On paper the winch is the weaker of the two, but the eyebolt figure is the least trustworthy number on site. The working load of 3.0 kN applies to the bolt, and only if it is correctly embedded. The actual failure mode is pull-out of the resin anchor from the slab, and that capacity depends on slab thickness, edge distance, concrete strength and hole cleaning - none of which is recorded. A thin slab or an anchor close to an edge can fail far below 3 kN, and a single anchor has no redundancy if it does.
Action before the lift:
- Do not start. Treat the anchorage as unverified.
- Have the slab thickness and edge distance established and the anchor capacity confirmed against the 1.28 kN line pull with a proper factor (a minimum of 2 is the usual floor, more for a shock-loaded or overhead-adjacent pull).
- If that cannot be done, add a second, independent anchor or use a rated deadman/ballast, and check the rope and shackle ratings as well.