High-Altitude Recovery Winch Overheat and Rope Damage
A defence recovery vehicle is on user trials at a high-altitude site (4,200 m, −18 °C). The demonstration requires winching a stalled 22 t 6×6 truck up a 28% slope with loose scree. The winch is rated 25 t on the first layer, and the pull is 40 m. After nine minutes the hydraulic oil temperature is 96 °C against an 85 °C limit; drum pressure swings between 180 and 240 bar although the relief valve is set at 210 bar. The wire rope has a tight kink 3 m behind the hook. The crew has no spare rope, one 20 t snatch block, and 90 minutes of daylight. Wind is 25 km/h. The trial officer wants either to finish the pull or convert to a two-part line. The vehicle is also the only recovery asset within 60 km, and the slope anchor is a buried deadman rated 30 t.
1. What should the trial officer do in the next 10 minutes, and why are the apparent alternatives unsafe?
Read the worked answer
Stop the pull and hold the load on the winch brake and deadman. The kink is a rejectable rope defect; continuing shock-loads it at 22 t, which is already 88% of the 25 t first-layer rating before slope and altitude effects. A two-part line would roughly halve line tension and drum load, but it doubles rope length, needs a suitable block/anchor geometry, and takes time. It is acceptable only after the kinked section is removed or the rope is replaced. Finishing the 40 m pull is not acceptable because oil is 11 °C over limit and pressure is oscillating ±30 bar around the 210 bar relief setting. Safe sequence: secure the truck, let the hydraulic system cool, inspect the rope, verify the 30 t deadman and block rating, then decide on a two-part line with a revised plan. If no sound rope length remains, abort the demonstration.
2. Separate the hydraulic symptoms from the rigging symptoms. What are the most likely causes, and what checks would you order before blaming the winch?
Read the worked answer
Hydraulic: 96 °C after nine minutes means heat input exceeds cooling. Likely causes are continuous operation near the relief setting, low oil level, a blocked or dirty cooler, reduced air-cooled cooler performance at altitude, or incorrect oil viscosity at −18 °C. Pressure swinging 180–240 bar against a 210 bar setting suggests relief-valve chatter from contamination, air entrainment, or pump wear; load surges on scree can add variation, but a steady ±30 bar swing is not normal. Rigging: the kink is mechanical damage from bad spooling or a side load, not an oil-temperature effect. Order checks of oil level and condition, cooler airflow, relief-valve setting and contamination, pump inlet for air leaks, and the rope history. Do not raise the relief setting to hide the symptom; that overloads the drum and rope.
3. Define the evidence you would require before a repeat trial, including acceptance and stop criteria.
Read the worked answer
Require a signed pre-trial record: rope inspected and the kinked section cut out or the rope replaced, with remaining length and termination certified; two-part line rigging calculation covering line tension, block load, anchor load and fleet angle; oil sampled and within the contamination limit; cooler cleaned; relief valve verified at 210 bar; pressure gauge calibrated. Trial criteria: 22 t load on the 28% slope, 40 m pull, oil temperature stable below 80 °C, pressure held within 200–220 bar, no rope strand break or kink, and a 10-minute hold at the end. Stop criteria: oil reaches 85 °C, pressure goes outside 200–220 bar, any rope damage appears, or the anchor moves. A successful pull at 15 t does not qualify the 22 t case. Brief the crew on abort signals and keep the area below the load clear.