Pete Bannister

F=MxV force= mass x velocity

F=MxV force= mass x velocity

Some good points have already being made. When I started climbing in 1970's ( rock that is, I've only recently taken to the trees) we were taught the bowline as the standard attachment knot. It's a great knot because of easy of untying and because you can, with practise tie it one-handed. As has been said, its eminently sensible to put a 'stopper' knot on the working end (most climbers use a thumb knot). The rewoven figure 8 is now the standard tie in because it has the great advantage of being very difficult to get wrong! Whilst a spliced eye is stronger in all respects than a knot its good to learn these basic tie-in knots by rote because you will at some point need to improvise in the field. Its good to buy the best gear you can afford: usually the most expensive! Good gear generally pays off at some point and if nothing else it just makes life and little better

As you guys are dealing with the volume and mass of 'cylinders' two useful rules of thumb might be 1) you can readily judge the relative mass of a piece of wood by placing it in water..if it sinks its more than 1000 kg /m3 and if it floats its less than this. 2) Useful to remember that if you double the diameter of a circle you quadruple the area. Its quite easy to forget this in the field; I have done so in a different context..wont do it again though!

Hi’ just joined your forum as an interested amateur. I’ve viewed the various links referred to in the comments on this thread and I'm a little mystified as to why arborists appear to use a simple pulley block to lower large loads. The mechanical advantage gained from using a simple block is only from the increased length of rope used to absorb the force. Depending on the rope and the length in which the force can be applied, internal friction and elasticity will absorb a considerable degree of the initial dynamic force. (This fact doesnt get mentioned in some of the links refered to but its a major means of energy absorbrion in any rope system.) Clearly, I can see the point of using more rather than less rope length. However, if you use a compound pulley system (traditional block and tackle) in place of your single pulley you can easily reduce the resultant load to be resisted at ground level ( x 4 or 5 easily). It would also reduce the resultant high-level load (the load on the tree and the strop) by the same factor if the rope is allowed to run through the system whilst breaking. I’m wondering, is it the weight and awkwardness of raising a compound pulley system into the tree, or would snagging be an issue? Hope my point is not too stupid!