A square or reef knot is a binding knot formed by two oppositely handed overhand knots. This calculator multiplies an entered straight-rope strength by an entered retained fraction; it does not determine a knot rating, safe working load or suitability for life-safety or lifting.
Square or Reef Knot · Entered-Assumption Ledger
Explore arithmetic from an entered rope strength, retained fraction, diameter and applied load.
Equation Used
- Rope strength and retained fraction are user-entered assumptions.
- The lbf value is only a unit conversion.
- Applied fraction and headroom are arithmetic comparisons, not safety factors.
- Entered diameter is reported but no tail prescription is inferred.
- Material, condition, tying quality, load history, standards and safety are excluded.
The secondary figure illustrates the named crossing pattern only; line widths and paths are not a load model.
Entered-assumption ledger
The selected retained-strength assumption is F_selected=fF_rope. The ledger also converts that value to pounds-force, compares entered load with it arithmetically and repeats the entered rope diameter.
What the calculator determines
Use it to inspect the consequences of values you enter. Do not use it to certify rope, knot, rigging, lifting, fall-protection or rescue capacity.
Exact selected relationships
F_selected=fF_rope; F_lbf=0.2248089431F_selected; applied fraction=F_load/F_selected; arithmetic headroom=F_selected-F_load.
Selected-input example
At entered rope strength 10,000 N, retained fraction 0.45 and applied load 1,000 N, selected retained strength is 4,500 N or 1,011.6 lbf, applied fraction is 0.222 and arithmetic headroom is 3,500 N.
Not a rope or knot rating
Rope material, construction, diameter tolerance, age, damage, wetting, contamination, bend radius, tying quality, dressing, cyclic loading, temperature, terminations, safety factors and governing standards are excluded.
Questions
Is 0.45 universally safe?
No. It is an entered assumption, not a design recommendation.
Is the displayed ratio a safety factor?
No. It is only applied load divided by the selected assumed strength.
Does this prescribe tail length?
No. The unsupported six-diameter rule has been removed.
Authoritative references
- U.S. Navy/Coast Guard Salvors' Handbook — context-specific fiber-rope strength reductions and preference for splices in synthetic rope.
- U.S. Army TM 3-34.86 — knot identification and comparison with sheet bends.
- OSHA, Review of Rope Grab Knot — warns that knots can significantly reduce lifeline strength.
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