How much leeward-shroud slack is normal when sailing, and how should I check rig tension?
When my yacht heels going upwind, the leeward shrouds feel much looser than the windward ones. How much slack is acceptable, and how can I check the tension without overtightening the rig?
Answer
Your leeward cap shrouds should lose some tension as the yacht heels, but stay snug rather than hang loose or flap when close-hauled in a fresh breeze. Check mast alignment and rig condition first, set the specified tension at the berth, then check it under sail, adjusting both sides equally.
Normal leeward shroud tension
The windward shrouds take more load as the sails pull the mast sideways, so the two sides will feel different. A shroud that feels less firm is different from one that visibly slackens, bows freely or snatches tight with each wave.
Start with the cap shrouds, which support the upper mast through the spreaders. As a practical sailing check, the leeward caps should remain snug at about 20 degrees of heel in roughly 15 knots of breeze, subject to the mast maker's instructions. Both sides need not feel equally tight under sail.
Lowers and intermediates need separate attention. They help control mast shape, and their correct tension depends on the spreader arrangement, mast section and rig design. Do not tighten every wire to the same feel. Use the prescribed settings and check that the mast remains properly supported and aligned.
Inspect the rig first
Extra turns on a bottle screw will not cure a moving chainplate or a sinking mast support. Before tuning, inspect:
- Wire and terminals: broken strands, rust staining, cracks around swages and sharp bends where wire enters a terminal.
- Chainplates and their attachments: movement, leaks, cracked surrounding laminate and loose fastenings below deck.
- Mast support: movement at the step, compression-post damage and deck distortion.
- Spreaders and bottle screws: secure fittings, correct spreader alignment, adequate thread engagement and free-running threads.
If a terminal, chainplate or mast support shows cracking or movement, stop sailing until it has been assessed.
With the boat upright in sheltered water, sight up the mainsail track for sideways bends. Check that the masthead is centred by taking the same main halyard to matching points on each side, pulling with consistent tension. Keep the halyard clear of obstructions.
Measure tension at the berth
Find the tuning instructions for your mast and boat. Masthead rigs, fractional rigs with swept spreaders, and discontinuous rigs require different sequences and tensions. On discontinuous rigs, the diagonals may need to start very loose because tensioning the verticals also loads them.
For wire rigging, use a Loos or equivalent tension gauge matched to the wire diameter and construction. Measure the wire itself, not its terminal, and follow the gauge's conversion table.