How to use this calculator
- Enter design load. Use the load for the shroud, stay or rigging member being checked.
- Enter safety factor. Use the target factor required by the designer, rigger, class rule or manufacturer.
- Enter selected wire data. Use the exact wire breaking strength and diameter from supplier data.
- Check utilization and stretch. Review strength margin, initial tension and elastic stretch before professional review.
How it works
Required minimum breaking strength is design load times target safety factor:
MBS_required = design_load x safety_factor
The selected safety factor is the selected wire breaking strength divided by design load:
SF_selected = MBS_selected / design_load
Strength utilization compares required and selected breaking strength:
utilization = MBS_required / MBS_selected
Elastic stretch at initial tension uses a simple axial relation:
stretch = F_initial x L / (E x A)
For measured replacement length and turnbuckle reserve, use the standing rigging spec calculator.
Worked example
Verified against the live calculator
A 1000 lbf design load with a 4x safety factor
requires 4000 lbf minimum breaking strength. A selected wire
with 5000 lbf breaking strength gives a selected safety factor
of 5x. At 15% initial tension, the initial
tension load is 750 lbf.
Frequently asked questions
How do you size standing rigging wire?
A basic sizing screen compares selected wire breaking strength with design load times target safety factor. The selected wire passes this arithmetic screen when selected breaking strength is at least the required breaking strength.
Can this choose the exact wire diameter for my boat?
No. It checks entered load and wire data. Final wire diameter depends on rig geometry, righting moment, chainplates, terminals, fatigue, corrosion, class rules, manufacturer data and a qualified rigger or designer.
Why enter selected breaking strength separately from wire diameter?
Real minimum breaking strength depends on wire construction, alloy, strand count, terminal details and manufacturer. Nominal diameter alone is not enough for final sizing.
What does elastic stretch mean here?
It is a first-pass axial stretch estimate from initial tension, span length, effective modulus and estimated metallic area. It is not a full rig tune model.
Method & assumptions
- Uses entered selected wire breaking strength; diameter alone is not treated as authoritative.
- Elastic stretch uses nominal wire diameter, area factor and effective modulus as a screening estimate.
- Does not model mast geometry, righting moment, fatigue, corrosion, terminals, swage quality, toggles, chainplates, spreaders, shock load, inspection intervals or class/manufacturer rules.
- Standing rigging is safety-critical. Use a qualified rigger, surveyor or naval architect for final sizing and inspection.