Forces during belaying

A fallen climber generates a certain force on the rope with his/her fall. At the same time, however, the belayer from below who caught the rope in the belay device is acting on the rope. As a result the rope tightens; significant impact force is exerted upon it. This is transferred to the intermediate protection through which the rope passes. It is, however, good to realise once again a relatively important thing – that two forces are acting on the intermediate protection. One is transferred along the rope leading from the fallen climber, the second from the belayer! And the intermediate protection is strained by the vector sum of these two forces. Of course, the matter is somewhat complicated by the fact that friction of the rope against the carabiner (or carabiners) of the intermediate protection also enters into play. The rope, since it is flexible, is stretched as a result of loading, understandably always in the direction of the fallen climber, as his free fall is the event which adds the energy. The tension of the rope to the belayer is only a reaction. The friction of the rope against the carabiner therefore actually helps to brake the fall of the fallen climber. And the force in the strand of rope leading to the belayer is reduced by this very braking force.

Distribution of forces.

Distribution of forces.

Another element which has an influence on the overall loading of the intermediate protection is the angle formed by both strands of rope (to the belayer, and to the fallen climber). Here a dependency is created – the sharper the angle between the strands of rope, the greater the total force acting on the intermediate protection, but at the same time the friction of the rope in the loop on the carabiner is also greater, therefore the force acting in the strand of rope leading to the belayer is less. And on the other hand – the more obtuse the angle between the strands of rope, the less the total force acting on the intermediate protection, but also the force of friction on the rope in the loop on the carabiner also decreases, so the force acting on the strand of rope leading to the belayer is greater. Here are three model situations approximately expressing this dependency:

  • both strands of rope lead in the line of fall
  • the strand of rope leading to the belayer is led slightly from the side
  • strands of rope forming a 90° angle
The influence of the angle of the strand of the rope entering and emerging from the point of intermediate protection on overall loading

The influence of the angle of the strand of the rope entering and emerging from the point of intermediate protection on overall loading

At the moment of catching a fall the highest point of intermediate protection reached is the most heavily strained, where when catching the fall the rope is reversed (this point of intermediate protection actually becomes the point of reversal). Of course, even so the other points of intermediate protection are partially loaded as well and thereby contribute with their friction to absorbing the energy of the fall.

More in e-book.

Title Part 3Mountaineering Methodology – Part 3 – Belaying and Rappelling

ISBN 978-80-87715-09-3

MMPublishing, 2013

Available for download from Apple iTunes (in the Books section).

For example U.S. store – link

Another countries – look on the page Download

See layout.

Another possibility is Google Play. This version is a simplified (as PDF).

Title Part 3 GPMountaineering Methodology – Part 3 – Belaying and Rappelling

ISBN 978-80-87715-14-7

MMPublishing, 2014

Available for download from Google Play.