The historical chain stop shown by Hiscox is a pivoted pawl that bears against a chain link to hold the cable. Raising the pawl clears the chain for movement. The animation illustrates that arrangement; the accompanying span-and-sag calculation is a separate static-equilibrium comparison.
Chain Stop Interactive Calculator
Watch the chain-stop pawl lift, clear the moving chain and lower again. The two sliders control the separate static chain-span diagram below it, showing how span and vertical drop affect force under a 1 kN central load.
Equation Used
- Static 1 kN central point load; equal-height supports.
- Two straight, flexible, tension-only segments with negligible self-weight.
- Drop s is measured in the loaded configuration, not initial slack before an impact.
- Pawl geometry and animation timing are illustrative and independent of the span inputs.
- No impact, elasticity, anchorage rating or stopper strength calculation.
The upper view shows a pivoted pawl holding and releasing a chain. Below it, a separate static span diagram shows how span and loaded drop affect horizontal reaction and segment tension. Neither model predicts impact loads, foundation performance or stopper capacity.
A pawl holds a chain link
Hiscox figure 806 identifies a chain stop for a cable. The drawing shows a pivoted lever whose lower tip bears against the chain. Lifting the tip releases the chain path; lowering it restores the holding position.
The animation separates those stages: lift, advance, lower and hold. The chain moves only while the pawl is clear. The bracket and chain dimensions are illustrative, and the view does not establish a working load or a release procedure under tension.
Holding a chain at its support
A chain stopper transfers load from a held chain into its supporting structure. Actual deck fittings use a base and an engaging bar or pawl matched to the chain. Fountom describes this arrangement for anchor chains.
This historical mechanism is different from a chain hung between posts as a visual access barrier. Nothing in this calculator establishes vehicle-restraint performance.
Separate static span-force comparison
The static calculator considers a separate geometry: two straight chain segments between level supports carrying a central downward load P. The central point is s below the supports and the horizontal span is L.
Each support carries vertical component V = P/2. The segment angle is θ = atan(2s/L). From equilibrium, horizontal component H = V/tan θ = PL/(4s), and segment tension is T = √(H²+V²).
The displayed comparison fixes P at 1 kN. This is a static force diagram, not a catenary with distributed self-weight and not a vehicle-impact model. The span sliders do not describe the pawl above it.
Default static example
For L = 3 m, s = 0.30 m and P = 1 kN, the segment angle is 11.31°. Each horizontal reaction is 2.50 kN and each vertical reaction is 0.50 kN. Total tension in each segment is 2.55 kN.
Doubling the loaded drop to 0.60 m halves the horizontal reaction to 1.25 kN. Total segment tension becomes about 1.35 kN because the 0.50 kN vertical component remains. These results do not rate a chain, post, foundation or pawl.
Two models with different purposes
The upper animation explains engagement and clearance in the historical chain-stop arrangement. Contact stresses, chain fit, locking details and supporting structure require information absent from the illustration.
The lower calculator explains static force amplification as a loaded chain becomes flatter. It omits chain weight, stretch and dynamic loading. Its slider range is an educational range, not an approved operating envelope.
Calculator questions
Why are the pawl and span diagram separate?
They describe different arrangements. The upper view explains the historical chain stop; the lower view compares static forces in a span with a central load.
Is horizontal reaction the total chain tension?
No. Total tension also includes the vertical component. Both values are displayed.
Does the drop represent slack before impact?
No. It is the vertical drop in the loaded static geometry shown.
Can this rate a vehicle barrier or anchor-chain stopper?
No. Neither model calculates component strength or dynamic impact performance.
Actuator engineering note for Chain Stop Mechanism
In a chain stop mechanism problem, the actuator is usually selected after the load path is understood. The important value is not just the weight being moved, but the force at the actuator pin after lever ratio, angle, friction, and worst-case position are included.
With leverage, force is traded against travel. A bracket change that improves force can also increase required stroke, slow the output motion, or move the actuator into a poor mounting angle.
For a separate actuator-operated pawl, check the load direction, bracket spacing and force throughout travel. The span calculation does not determine the force needed to lift or release the pawl.
- Calculate actuator force at the worst bracket angle, not just at mid-stroke.
- Check stroke, retracted length, and extended length against the mechanism envelope.
- Confirm the structure can accept the higher loads created by a stronger actuator.
For a FIRGELLI actuator application, run the FIRGELLI actuator force calculator, then compare available stroke, force, and mounting envelope in the FIRGELLI linear actuator range. If the goal is to replace an existing unit, use the linear actuator replacement finder before assuming the new actuator is a direct fit.
References & Further Reading
- Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances (1901), printed page 212, figure 806: chain-stop pawl.
- Fountom, Chain Stopper: base, pivoted bar or pawl and chain-holding function.
- Engineering Statics: 2D Particle Equilibrium: force-component equilibrium used in the separate span comparison.
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