The Whyalla & Districts 4WD Club


An illustration of why Snatch Straps and/or Winch Extension Straps MUST NEVER be joined with shackles.

Determine Characteristics of 8000kg Breaking Strain 9m Snatch Strap.

A 550kg Test Weight was hung from the Snatch Strap producing 260mm Elongation.

From Hookes Law

Determine Energy Produced by a Recovering 4WD.

For a 2.5 Tonne 4WD travelling at 6km/h,
The Kinetic Energy available, KE4WD = 1/2 m v2

The author, undertaking research for this article

Checking Stretch of Snatch Strap.

If all the Kinetic Energy of the Recovering 4WD is transferred to Elastic Energy in the Snatch Strap then the stretch of the strap can be determined. (Assuming no losses due to friction)

From Energy Conservation,

And from Hookes Law the Force Stored in the Snatch Straps is,

Determine Speed of Shackle if Snatch Strap Breaks.

If all the Elastic Energy of the Snatch Strap is transferred to Kinetic Energy in the Shackle then the peak Speed of the Shackle as the Snatch Strap returns to it's 9.0m length can be determined. (Assuming no losses due to friction)

From Energy Conservation,

This shackle speed gives no time for any reaction to get out of the way and would cause tremendous damage to whatever it contacts.

Snatch Straps and/or Winch Extension Strap should always be joined using the loops on the ends of the Straps as illustrated below.

References: Introduction to Physics for Scientists and Engineers. By Frederick J. Bueche
This Page Contributed by Club Member Andrew K.