Testing standard
Fibre ropes — Determination of certain physical and mechanical properties
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ISO 2307 determines six properties of a fibre rope in one procedure: linear density, diameter, lay length, braid pitch, elongation and breaking force. Every dimensional measurement is taken at a calculated reference tension, and the breaking force is reported for each test piece as spliced or unspliced, never averaged. The current edition is ISO 2307:2019.
A length of rope is taken at random from a manufacturing batch, laid out straight, marked and mounted at a defined effective length between its terminations. A reference tension is applied, and the diameter, the lay length or braid pitch and the gauge length between the marks are all measured while the rope is held under it. The rope is then bedded in by cycling ten times — or three times, as the alternative the method allows — between the reference tension and half the minimum specified breaking force. The gauge length is measured again at that half-load point to give elongation, then the tension is raised at the same speed until the rope breaks. Linear density is determined separately, on a fresh two-metre length weighed after being held at the reference tension.
Six properties in one document: linear density, diameter, lay length, braid pitch, elongation and breaking force, with methods for water repellency and for lubrication and finish content added for natural-fibre ropes when a customer asks for them. They travel together because none of them is defined without the others. An unloaded rope has no measurable diameter and no measurable length — it shortens and fattens the moment tension comes off — so every dimensional measurement is taken at a reference tension calculated from the rope reference number, never chosen by the operator. The breaking force is reported for each test piece and deliberately not averaged, and it has to be stated as spliced or unspliced, because the termination is part of the result rather than a detail of the rigging.
The termination is part of the specimen. Most of the specimen rules exist to stop the rope breaking in the eye or at the grip instead of in the rope.
Handle the test piece so it cannot unlay. A rope that has started to open at the cut end is no longer the rope that left the machine.
F_T = (n_ref² / 8) × 0,01
Applied when measuring linear density and lay length or braid pitch. Tabulated in Annex A with a ±5 % tolerance.
ρ₁ = m / l₁
Expressed in kilotex. Measured on a fresh length of 2 m or more, not on the piece that was broken.
E = ((l₃ − l₂) × 100) / l₂
Both lengths are measured between the same two w marks, so the elongation is referred to the rope under tension rather than to a slack length.
l_p = l_n / n
The maximum force recorded, expressed in kilonewtons
Reported for each test piece individually. The mean is not calculated, and the report must say whether the value is spliced or unspliced.
A rope taken to rupture in more than one pull can give a different result. The stroke and bed length have to allow one continuous pull.
Rope, cord and twine are clamped against a curved capstan body, so the force enters the rope gradually along the wrap instead of at one short clamped section. That is what stops the break happening at the grip rather than in the rope.
SpecificationsISO 2307 asks for the breaking force to be measured to ±1 %, so the cell has to be chosen for the rope rather than for the frame. Rope sizes across a range means more than one capacity.
SpecificationsForce, stroke, and a termination that does not become the specimen. The machine must measure the breaking force to ±1 %, and the stroke and bed length should be long enough to take the rope to rupture in one continuous pull; the standard notes that a specimen broken over more than one pull can give a different answer. Three arrangements are recognised — bollard-type grips, pins for eye splices, and wedge grips. A bollard or capstan must be at least ten times the rope diameter and a pin at least twice it. Speed goes with the arrangement: 250 mm/min ± 50 mm/min on wedge or bollard grips, and 2 % to 12 % of the pin-to-pin length per minute for spliced ropes.
Breaking in the eye or at the termination, which is what the splice rules exist to prevent — a break outside the marked zone is accepted only at 90 % or more of the specified value, and the standard warns against scaling such a result up by 10/9 to rescue it. Shortening the bedding-in, so the reported elongation still contains the constructional stretch the cycling was there to remove; the cycle count belongs in the report for that reason. Measuring diameter with no tension on the rope. Averaging the breaking forces, which the method does not ask for. And walking up to a loaded rope to read a gauge length by hand, which is the one item here that injures people rather than results.
The standard recognises three machine types, and each brings its own rule about how big the termination has to be.
| Bollard grips | Pins for eye splices | Wedge grips | |
|---|---|---|---|
| Termination | Rope wrapped on the bollard | Eye splice over a pin | Rope clamped in wedges |
| Size rule | Bollard at least 10 × rope diameter | Pin at least 2 × rope diameter | No diameter rule stated |
| Test speed | 250 mm/min ± 50 mm/min | 2 % to 12 % of pin-to-pin length per minute | 250 mm/min ± 50 mm/min |
| Typical use | Ropes below reference number 20 | Ropes of reference number 20 and above | Ropes below reference number 20 |
The termination decides the number. A spliced breaking force and an unspliced breaking force are different quantities, and a report that does not say which was measured cannot be checked against a specification.
ISO 2307 is the international method for determining certain physical and mechanical properties of fibre ropes: linear density, diameter, lay length, braid pitch, elongation and breaking force. The current edition is ISO 2307:2019, the fifth, which replaced ISO 2307:2010 and was confirmed on systematic review in 2025.
It is a small tension, calculated from the rope's reference number as the reference number squared divided by eight, times 0,01, in kilonewtons. It exists because an unloaded rope has no defined size: it shortens and thickens as soon as tension comes off. Diameter, lay length, braid pitch, linear density and the gauge length for elongation are all measured with the rope held at that tension, so two laboratories measuring the same rope arrive at the same figures.
To take the constructional stretch out. A new rope contains slack that is bedded down the first few times it is loaded, and elongation measured without that step is mostly a measurement of the rope tightening rather than of the fibre stretching. The method calls for ten cycles between the reference tension and half the minimum breaking force, or three by agreement, and the number used has to be stated in the report because it changes the answer.
Whether the rope was terminated with an eye splice or held directly. A splice reduces the strength of a rope, so the two numbers are not the same and a specification names one of them. ISO 2307 requires the report to say which was measured. For an unspliced value the break must fall inside the marked zone, or outside it at 90 % or more of the specified value.
No. The standard allows a break outside the r marks to count if it reaches at least 90 % of the specified value, and then says explicitly that it should not be assumed the true breaking force would be found by multiplying the result by 10/9. The allowance exists to avoid discarding a valid test, not to convert a low result into a passing one.
It depends on how the rope is held. On wedge grips or bollard grips the speed should be 250 mm/min ± 50 mm/min. On spliced ropes tested over pins it should be between 2 % and 12 % of the pin-to-pin length per minute. Either may be varied if it is specified and documented in the test report. The fifth edition changed the test speed, so a figure from the 2010 edition was not produced this way.
The effective length between terminations must be at least five lays or braid pitches, or 400 mm, whichever is greater, and the marked gauge length inside it must exceed 400 mm. In practice the machine has to be long enough that the rope reaches rupture in one continuous pull, because the standard notes that breaking a specimen over more than one pull can affect the result.
No, and this catches people out. Linear density, lay length and elongation are reported as the arithmetic mean of the test pieces in the batch, but the breaking force is reported for each test piece individually with no mean calculated. If one test falls below the minimum breaking strength the manufacturer may run two further tests, and the rope passes only if both of those are above it.
Annex B of ISO 2307 gives alternative procedures for ropes with high breaking forces, which derive the rope strength from yarn test results. Those procedures are available only by agreement between the parties, and where they are used the test report must state that the breaking strength was calculated from yarn results rather than measured on the rope.
Dak verifies against whichever standard the method names, and where a class applies our frames sit a class tighter than it asks.
| The method asks for | Dak supplies | |
|---|---|---|
| Capacity | Very wide — light cordage of reference number 4 breaks well under 1 kN while heavy mooring lines run into hundreds of kN, so the frame is chosen for the rope; where a rope is too strong to break whole, Annex B allows the strength to be derived from yarn results by agreement | Load cells from 1 kg to 60 ton on the Series 7200, and 0.5 to 100 kN on the Series 9000 |
| Force accuracy | Breaking force measured to an accuracy of ±1 % | ISO 7500-1 Class 0.5, verified to ASTM E4, DIN 51221 and BS 1610 |
| Gripping | Bollard or capstan grips, pins for eye splices, or wedge grips | Our split capstan grips, built to the specimen |
| Environment | Ambient atmosphere; the ISO 139 atmosphere for at least 48 h in cases of dispute | 3009 series chambers, −150 °C to +400 °C — temperature only |
This page describes the method as practised. The governing text is the current edition from the issuing body. Tell us what you are testing and we will answer with the machine, the fixture and a quotation.
