How to use this calculator
- Enter wire strength. Use the exact selected wire breaking strength from manufacturer or rigger data.
- Set target percent. Enter the tension target as a percent of breaking strength.
- Enter measured tension. Use a calibrated gauge reading or trusted measured load.
- Enter wire stiffness data. Set span length, diameter, effective modulus and metallic area factor.
- Check turns and predicted tension. Review required turns, entered turnbuckle take-up, predicted tension and utilization before qualified review.
How it works
Target tension is calculated from selected wire breaking strength: F_target = MBS_selected x target_percent / 100 Measured error is target tension minus measured tension.
Wire axial stiffness is estimated from the entered span, modulus and metallic area: k = E x A / L stretch = F / k Required take-up is the tension error divided by stiffness.
Turnbuckle take-up is converted from thread pitch:
take_up = pitch x turns x moving_threaded_ends
The predicted tension change is k x take_up. For wire strength
sizing, use the standing rigging wire size calculator.
For replacement stay or shroud length, use the
standing rigging spec calculator.
For general stretch, use the wire rope stretch calculator.
Worked example
Verified against the live calculator
A 5000 lbf selected wire with a 15% target has a
750 lbf target tension. If measured tension is
650 lbf, a 30 ft span of 1/4 in
wire with 190 GPa effective modulus and 0.75
area factor needs about 0.035 in of take-up, or about
0.35 turns on a two-ended 20 TPI turnbuckle.
Frequently asked questions
How do you calculate a standing rigging tension target?
A common first-pass screen expresses target tension as a percent of selected wire breaking strength: target tension = selected breaking strength times target percent divided by 100.
How does the turnbuckle turns estimate work?
The calculator converts turns into take-up from thread pitch and the number of threaded ends moving, then multiplies take-up by estimated wire axial stiffness.
Can this replace a Loos gauge chart or a rigger?
No. Gauge calibration, wire construction, boat type, mast geometry, terminals, chainplates, fatigue, corrosion and class or manufacturer requirements must be checked with qualified rigging guidance.
Why enter wire diameter if breaking strength is already entered?
Breaking strength sets the tension target, while diameter, modulus, span and area factor estimate stiffness and stretch. Both are needed for the turnbuckle take-up screen.
Method & assumptions
- Target tension is based on entered selected wire breaking strength, not inferred from diameter alone.
- Wire stiffness uses nominal diameter, area factor and effective modulus as a screening estimate.
- Turnbuckle take-up assumes the entered pitch is linear take-up per threaded end per turn.
- Does not model mast bend, spreader geometry, compression, chainplates, terminal stretch, toggle geometry, fatigue, corrosion, dynamic sailing loads, gauge calibration or class/manufacturer rules.
- Standing rigging is safety-critical. Use a qualified rigger, surveyor or naval architect for final setup and inspection.