Simon Wilson
New member
Mr Mike said:I know cavers are generally better rope riggers than mine explorers and have this question about a pull through scenario that we have been debating on aditnow, basically its a pull through off 2 anchors that are in line to each other and horizontal (as for a Y-hang) most of us say it is fine, but one is saying its forming an American Death Triangle) see:
http://www.aditnow.co.uk/Community/viewtopic.aspx?p=176601#msg176601
My question, is it as bad as made out or perfectly acceptable to use like this? Thanks.
Both views are partly correct. The American death triangle is a theoretical way of explaining how a rope in a triangle will half the angle between the lines of force. The accepted minimum angle for a Y hang is 120 degrees because this is the angle which produces forces on the anchors equal to the force on the live rope. If the rope forms a triangle, the angle at which the force is applied is half of the angle between the live rope and the top of the triangle this is what is described as amplifying the force. An angle between the lines of force of 120 would be achieved if the triangle was an equilateral triangle.
If a rope is passed through two anchors, when the abseiler is near the bottom of the rope the effective angle approaches 90 degrees. If the load is applied close to the anchors and the distance is less than the distance that the anchors are apart then the force applied to the anchors could be greater than the force on the live ropes. In practice it would be impossible to apply the load that close to the anchors. So the angle will always be less than 120 degrees.
Whoever it was that mentioned the American death triangle, they were correct in bringing the phenomenon to people's attention because it is something that people should be aware of although in this case it isn't a problem.