A timber hitch wraps a rope around timber, turns the working end around the standing part, and coils the tail back around itself. The U.S. Army manual notes that coil pressure tightens under strain and also warns that the hitch used alone may untie under slack or sudden strain.
Timber Hitch Interactive Calculator
Set an illustrative timber diameter, displayed wrap angle, tail-coil count and rope diameter. Results are geometric lengths and ratios only.
Equation Used
- Timber and rope diameters are illustrative circular dimensions.
- Displayed wrap angle is measured about the timber centerline.
- Each displayed tail coil is assigned a centerline circumference pi*d for comparison only.
- The drawing does not model rope lay, compression, bending, surface conformity or knot dressing.
- Friction, holding capacity, slip, rope strength, shock, wear, dynamic loading, lifting and safe rigging are omitted.
Timber-hitch Topology
U.S. Army manual TM 3-34.86 describes the timber hitch as a hitch for moving heavy timber or poles. Its figure and text show the rope around the object, the working end turned around the standing part, and coils laid one over another.
The manual says strain tightens the hitch and that it loosens when strain is relieved. It also warns that a timber hitch used alone may become untied when the rope is slack or a sudden strain is applied.
What This Calculator Does
The calculator draws the hitch topology and reports the arc length associated with an entered display angle, the timber-to-rope diameter ratio, a schematic sum of circular tail-coil paths, and a six-diameter visual marker.
None of those values predicts knot grip, slip, capacity or suitability.
Display Geometry Only
diameter ratio = D/d
displayed coil-path sum = n pi d
six-diameter marker = 6d
The coil-path expression is a drawing convention. A dressed rope hitch does not consist of isolated circular coils of diameter d.
Worked Display Example
For D=300 mm, theta=300 degrees, n=3 and d=14 mm, displayed wrap arc is about 785.4 mm, timber/rope diameter ratio is about 21.4, displayed coil-path sum is about 131.9 mm and the six-diameter marker is 84 mm.
Assumptions and Limits
- Reference context: the timber-hitch arrangement and operational cautions described in the cited Army manual.
- Calculated: elementary display lengths and diameter ratio.
- Not calculated: capstan friction, holding power, efficiency, slip, required tail, rope strength, knot strength reduction, bending, crushing, shock, dynamic load, object rotation, inspection, redundancy, lifting or safe rigging.
Frequently Asked Questions
Does the calculator give timber-hitch capacity?
No.
Does the calculator predict holding force?
No. The drawing does not establish a contact or friction model for a dressed timber hitch. Its geometric outputs cannot be used as holding-force or capacity estimates.
Is six rope diameters a required tail?
No. It is only a display marker.
Do more displayed coils guarantee more holding power?
No capacity relation is asserted.
Can a timber hitch be trusted when slack or suddenly loaded?
The cited Army manual warns that the hitch used alone may become untied in those conditions.
Can this tool approve lifting or rigging?
No.
References
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