Selected tension is break-strength value times selected percentage. Selected sag distance is stay length times selected sag percentage. The 20% value is shown only as an arithmetic comparison—not a universal working limit.
Sloop Forestay · Selected Tension and Sag
Explore selected forestay tension and sag arithmetic without asserting a universal limit or performance prediction.
Equation Used
- Break strength is a selected value, not independently verified.
- Selected percentages are dimensionless arithmetic inputs.
- Rendered sag is a midpoint offset from a straight chord and is not a catenary solution.
- Rig geometry, materials, terminals, sails, loads, fatigue, performance and safety are excluded.
The 20% value is an arithmetic comparison. Tacking angle also depends on sail shape, trim, wind, hull and sea conditions.
Recognizable sloop with an exact sag reference
The side view shows one mast, mainsail and headsail. The forestay chord represents selected stay length, and the quadratic reference curve has the selected midpoint offset exactly equal to the chosen sag percentage of that chord.
What the calculator determines
Select break-strength value, tension percentage, stay length and sag percentage. The calculator reports selected tension, a selected 20% comparison value, sag distance and signed difference from that comparison.
Selected arithmetic
T = BS·p/100; T20 = 0.20BS; sag = L·s/100; difference = T20 − T.
Selected-input arithmetic
For BS = 60 kN, p = 15%, L = 10 m and s = 2%, selected tension is 9 kN, the 20% comparison is 12 kN and selected sag is 200 mm.
Selected references, not rig tuning
Actual allowable tension and useful sag depend on the complete rig, wire or rod type, terminals, mast and hull structure, rig geometry, sails, wind, sea state and manufacturer instructions. Pointing, tacking angle, fatigue, stability, strength and safety are not predicted.
Questions
Is 20% a universal working-load limit?
No. It is only a selected comparison reference here; published rigging guidance varies by rig component and configuration.
Does sag determine tacking angle?
No. Tacking angle also depends on sail shape, trim, wind, hull and sea conditions.
References & Further Reading
- Wikipedia contributors. Sloop. Wikipedia
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