If you are just starting out, you are going to need to know a lot of basic terminology. This will be a good starting point, and I will continue to update it as need be.
a. Rigging – use of ropes to lower and control sections of tree to the ground.
b. Rigging System – interaction of all elements used for rigging including points in the tree, slings, hardware, rope, force angles, etc.
c. Piece – the section of tree being rigged.
d. Rigging Line – main rope used to hold the weight of the piece.
e. Tag line – secondary rope used to control swing or directionality.
f. “Small Rigging” – piece can be carried or dragged by one or two people once on the ground.
g. “Big Rigging” – pieces that are too heavy for two people to carry, must be cut up once on the ground.
h. Positive/Overhead Rigging – rigging point is above the piece, used whenever possible.
i. Negative Rigging – rigging point is below the piece, used in the absence of other options, always involves shock loading.
j. Shock Loading – mass coming to a short, sudden stop. Can multiply peak forces by 10X or more.
k. Tension wood – fibers are being pulled apart.
l. Compression wood – fibers are being squeezed together.
m. Leverage – bending force being exerted at a distance from a fulcrum.
n. Mechanical Advantage – force amplification achieved by using a tool, mechanical device or machine system. In our line of work, this is usually achieved using ropes and pulleys, although there are other options, including come-alongs. Mechanical advantage always involves a trade-off: pulling distance for pulling power.
o. Friction – the force resisting the relative motion of solid surfaces sliding against each other. Friction produces heat which can damage both ropes/hardware as well as tree bark. Friction management is a key component to many aspects of tree climbing and rigging.
a. Tensile strength / Minimum Breaking Strength (MBS): the average breaking strength of a piece of equipment when pulled to failure under controlled conditions. Tensile strength is usually quoted in kN.
b. Kilonewton (kN): approximately 225 lb.
c. Minimum strength: as defined by safety legislation and regulations, life safety gear is required to have a tensile strength of at least 5000 lb (usually rounded up to 23 kN).
d. Working Load Limit (WLL): expressed as a fraction of the tensile strength, this is the maximum load that the equipment is rated for over a large number of cycles. Standards are rigging gear 5:1, climbing gear 10:1. For example, if a rigging line is rated for 5000 lb and the working load limit is 5:1, that means you can consistently load it with 1/5 of its tensile strength (i.e. 1000 lb). For a climbing line rated at 5000 lb, you can consistently load it with 1/10 of its tensile strength (i.e. 500 lb).
e. Cycles to Failure: Ropes and slings can only be exposed to heavy loads so many times before they eventually fail. Adherence to WLL guidelines will ensure long life for your equipment, this is why it is so important to know the history of your gear.
f. Static Rope: very low stretch (0.5-1.5% range). Rarely used in rigging.
g. Semi-static Rope: low stretch (1.5-4% range). This is standard arborist rope used for climbing and rigging.
h. Dynamic Rope: very high stretch (5-20% range). Used in mountain climbing to catch a lead climber during a fall to minimize injury.
i. Bend Ratio: when running a rope through a block or pulley, the minimum ratio of sheave to rope diameter is 4:1. This means that if we are using 1/2″ rope, the sheave must be at least 2″ in diameter. A more preferable ratio, as recommended by Samson Ropes, is 8:1, for maximum strength retention of the rope, meaning that a 1/2″ rope would be used with a pulley sheave diameter of 4″.
a. Moving Rope System (MRS) – Traditional climbing system, also known as DdRT (Doubled Rope Technique), wherein the climber’s line is terminated at their saddle, then run up and over a branch union (tie-in point), then back down to the climber and attached by a friction hitch (or mechanical device). From the friction hitch, the rope continues to the ground. This system forms a closed loop that can be made larger or smaller, thus allowing the climber to move towards or away from the tie-in point. Note that the entire length of rope is moving as the climber ascends or descends, making friction management an important concern.
b. Stationary Rope System (SRS) – Newer style climbing system, also known as SRT (Single Rope Technique), wherein the climber’s line is run up through a branch union (tie-in point), and either affixed to it directly, or run back to the ground where it is tied off. The climber is attached to the line by a friction hitch or mechanical device. In this setup, the climber can ascend and descend with consistent friction, as the rope remains stationary, i.e. the climber is moving along a fixed line.
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