6.6 Rigging Knots, Fiber Rope & Rope Work for Load Control
Key Takeaways
- Every knot reduces the strength of the rope it is tied in: a bowline retains roughly 55-60 percent of rope strength, a figure-eight about 65-75 percent, and a square knot barely 45 percent.
- Fiber rope and knots are for load control, hauling, and lashing — they are never a substitute for a rated sling, and a knot must never be tied in a synthetic web sling, roundsling, chain, or wire rope.
- The bowline forms a fixed non-slipping loop and is the default tagline and hand-line attachment; the clove hitch backed up with two half hitches secures a line to a round member.
- Working load for fiber rope is derived from a design factor of at least 5:1 applied to new rope strength, then further reduced for knots, age, abrasion, UV exposure, and chemical contact.
- A rigger controls a load with the tagline, not with their body: the line is held in an open hand and never wrapped, looped, or tied around a wrist, arm, or waist.
6.6 Rigging Knots, Fiber Rope & Rope Work for Load Control
The NCCER Advanced Rigger written specification lists "taglines and knots for load control" as a Rigging Practices topic, and the Rigger practical examination lists "rigging equipment and knots" as a scored task. Candidates are expected to identify a knot from a picture, name its application, and know what it costs the rope.
The governing principle is boundary-setting: fiber rope and knots control loads; rated slings carry loads. A knot is legitimate on a tagline, a hand line, a lashing, or a temporary anchor lanyard. A knot is never legitimate in a load path.
The Absolute Prohibition
Never tie a knot in a sling. A knot in a synthetic web sling or roundsling cuts its rated strength by 50 percent or more, because the knot forces an extremely tight bend radius and concentrates all tension into the outermost filaments at a single point. Knotting is equally prohibited in wire rope slings and alloy chain slings, where the "knot" is really a kink and permanently destroys the rope or link structure. A sling may only be shortened by an approved method — a proper choker, a rated shortening clutch or grab hook designed for that chain, or a shorter sling.
The Working Knots
| Knot / hitch | What it does | Where a rigger uses it | Approximate rope strength retained |
|---|---|---|---|
| Bowline | Forms a fixed loop that will not slip or tighten under load, and unties after loading | Tagline attachment to a load, hand lines, throwing a loop over a bollard or lug | ~55-60% |
| Figure-eight (and figure-eight on a bight) | Strong terminal loop; easy to inspect visually | Life-safety-adjacent lines, anchor loops where inspectability matters | ~65-75% |
| Clove hitch | Secures a line to a round member; adjustable | Attaching a tagline to a pipe or column — always backed up with two half hitches | ~60-65% |
| Two half hitches | Quick backup / finishing hitch | Backing up a clove hitch; securing a tail | ~60-65% |
| Timber hitch | Grips along the length of a round member and releases easily | Dragging or lashing timber, poles, and pipe | ~65-70% |
| Round turn and two half hitches | Takes load off the knot itself with a full wrap | Tying off to a post or ring under sustained tension | ~65-75% |
| Square (reef) knot | Joins two lines of equal size for lashing only | Binding and lashing — never for joining a load-bearing line | ~45% |
| Sheet bend / double sheet bend | Joins two lines of unequal diameter | Extending a hand line | ~50-55% |
The percentages are the exam point. A knot is a controlled bend plus a compression point, and both cost strength. Because the square knot retains the least and capsizes easily when the two lines differ in diameter, it is restricted to lashing. Because the bowline holds a fixed loop and still unties after being loaded, it is the rigger default.
Anatomy vocabulary
- Bight — a bend or loop in the rope that does not cross itself.
- Standing part — the long, load-carrying section of the line.
- Running end (working end) — the free end you tie with.
- Dressing — arranging the parts of a finished knot so they lie fair and parallel. An undressed knot loses far more strength than a dressed one and can capsize under shock.
Fiber Rope Selection & Design Factor
| Fiber | Strength | Stretch | Notes for riggers |
|---|---|---|---|
| Polyester | High | Low | Best all-around tagline material; holds strength when wet; resists UV and acids |
| Nylon | Highest of the common three | High (~20%+) | Absorbs shock well, but the stored energy makes a parting line dangerous; loses ~10-15% strength when wet; destroyed by acids |
| Polypropylene | Lowest | Moderate | Floats and resists chemicals, but degrades quickly in sunlight and melts at low temperature |
| Manila (natural) | Low | Low | Legacy material; rots, mildews, and loses strength unpredictably with age |
Fiber rope for rigging service is worked to a design factor of at least 5:1 against the new-rope breaking strength, and that working load must then be reduced further for every degrading condition present:
- Knots — apply the efficiency from the table above.
- Age and service — rope in service loses strength continuously; there is no way to test it in the field.
- Abrasion and glazing — fuzzy, cut, or shiny/melted fibers all mean removal.
- UV degradation — chalky, faded, powdery surface fibers on polypropylene or polyester.
- Chemical exposure — any acid contact on nylon, any strong caustic contact on polyester.
- Shock loading — a rope that has been shock loaded is removed, not re-rated.
Inspect fiber rope by opening the lay: untwist a section and look inside for powdered fiber, broken internal yarns, or discoloration. Powder inside the lay is internal abrasion and is a removal condition even when the outside looks sound.
Rope Work on the Load
- Attach to the load structure. A tagline goes on a structural corner, lug, or frame member of the load — never on a sling leg, hook, or shackle, where pulling can change sling geometry or unseat hardware.
- Two lines on long members. Long or wind-sensitive items such as beams, trusses, pipe spools, and rebar cages need two taglines at opposite distal ends so the crew can control rotation as well as swing.
- Length with clearance in mind. The line must be long enough to keep the handler outside the fall zone and clear of the load path, but not so long that it can foul on the structure, a scaffold, or an energized line. Use non-conductive rope near electrical hazards.
- Open hand, never wrapped. The line is held, never wrapped or tied around a wrist, hand, arm, or body. If the load surges, a wrapped line drags the rigger into the line of fire with no way to let go.
A rigger needs to shorten a synthetic web sling by about two feet to level a load. What is the correct action?
Which knot forms a fixed loop that will not slip or tighten under load and can still be untied after it has been loaded, making it the standard tagline attachment?
Why is the square (reef) knot restricted to lashing and binding rather than joining two load-bearing lines?
A rigger inspects a polyester tagline by opening the lay and finds fine powder inside between the strands, though the outer surface looks sound. What does this indicate?