Reference

Vehicle Recovery

Procedures for extraction of an immobilized vehicle. Covers winch anchor systems, mechanical advantage configurations, and extraction technique by substrate type. All procedures assume a single vehicle equipped with a forward-mounted winch rated at minimum 4,000 kg line pull.

Anchor systems

The winch line requires a fixed anchor point. Where natural anchors are unavailable, a ground anchor must be deployed. Anchor selection depends on substrate and available attachment points.

Natural anchors

Trees, rock formations, and structural remnants serve as natural anchors. Minimum trunk diameter for tree anchor: 300 mm at the attachment point. Wrap the tree protector strap at the lowest point where diameter is adequate. Do not attach to dead trees, trees with visible root exposure, or trees in saturated soil. Rock anchors require a feature that prevents strap migration under load—a horn, notch, or constriction. Structural remnants (concrete piers, steel posts, foundation walls) are acceptable if the structural member is intact and the foundation is stable. Assess structural integrity before loading.

Ground anchors — buried deadman

  1. Excavate a trench perpendicular to the intended pull direction. Depth: minimum 600 mm. Width: minimum 1,000 mm.
  2. Place the anchor bar (or a suitable substitute: spare tire, log, rock) at the bottom of the trench, oriented perpendicular to the pull direction.
  3. Attach the winch line or anchor strap to the center of the anchor bar. Route the line over the lip of the trench at the midpoint of the far wall.
  4. Backfill the trench, compacting the substrate in 150 mm lifts.
  5. Apply load gradually. Monitor for anchor migration. If the anchor displaces more than 100 mm under initial load, stop, excavate, and reset at greater depth.

Ground anchors — stake cluster

  1. Drive three or more stakes in a triangular pattern, 500 mm apart, oriented so that the pull load is distributed across all stakes. Minimum stake depth: 600 mm in firm soil, 900 mm in soft soil.
  2. Connect all stakes with a bridle strap or chain to equalize load.
  3. Attach the winch line to the bridle at its center point.
  4. Apply load gradually. Monitor individual stakes for migration. If any stake displaces, stop and add additional stakes to the cluster.
Not effective in sand, saturated soil, or substrate with bearing capacity below 50 kPa. Use buried deadman in these conditions.
Mechanical advantage

When the required extraction force exceeds the winch rated line pull, a snatch block configuration provides mechanical advantage. Each redirect through a snatch block approximately doubles the available pull force at the cost of halving the line speed and requiring additional line length.

Snatch block configurations
Configuration Mechanical advantage Effective pull (4,000 kg winch) Min. line length
Direct pull 1:1 4,000 kg 1× distance
Single redirect 2:1 8,000 kg 2× distance
Double redirect 3:1 12,000 kg 3× distance
Triple redirect 4:1 16,000 kg 4× distance
All rigging components (shackles, straps, snatch blocks) must be rated for the total system load, not the winch rating. A 2:1 configuration places the full system load on the anchor point. Inspect all components before each use.
Extraction by substrate

Sand

Reduce tire pressure to 100–120 kPa before winching. Lower pressure increases the tire contact patch and reduces resistance to forward motion. Clear sand from in front of all tires to below the axle line. If available, place traction boards or flat material (plywood, metal plate) in front of the drive tires. Winch at the lowest speed setting. Once the vehicle begins to move, maintain momentum. Re-inflate tires before continuing on firm surface.

Mud

Do not reduce tire pressure in mud—lower pressure increases the contact patch and increases suction force. Excavate mud from around all tires to below the tread. If the vehicle is sunk to the chassis, excavate around the chassis contact points to break the suction seal. Rocking the vehicle laterally before winching can break the suction. Apply winch load gradually; a sudden load on a suctioned vehicle can exceed anchor capacity. Expected extraction force: 1.5–3.0 × vehicle mass depending on suction depth.

Clay

Wet clay presents the highest resistance to extraction of any common substrate. Suction forces can exceed 2.5 × vehicle mass. Excavation around tires and chassis is essential. Break the suction seal before applying winch load. If the vehicle is deeply embedded, excavate a ramp in front of the drive tires at a gradient of no more than 15%. Mechanical advantage of 2:1 or 3:1 is frequently required.

Scree and loose rock

On scree slopes, the primary concern is uncontrolled movement during extraction. The vehicle may slide laterally or downhill as traction is regained. Chock the downhill wheels before beginning the extraction. Winch uphill whenever possible. If lateral extraction is unavoidable, use a secondary anchor line as a belay to prevent downhill slide. Tire pressure should be at the standard off-road setting (150–180 kPa).

Vegetation-bound surface

On surfaces where dense vegetation has grown around or through the vehicle path, extraction resistance may be higher than the substrate alone would suggest. Root systems, vines, and compacted organic material add to the total resistance. Cut vegetation from around the tires and undercarriage before winching. Expect extraction force to be 1.2–1.5 × the force predicted by substrate alone.

Revision

Procedures compiled from field application across all documented routes. Extraction force estimates based on direct measurement. Substrate-specific procedures tested in the conditions described.