Reefing and depowering: taking power out of the sails.

Why depower

An overpowered boat heels hard, builds weather helm and becomes harder to steer. North Sails' rule of thumb is that if you are fighting the helm or the rail is in the water, you need to flatten the sails or head up. Hiking only goes so far: Loe and Smith, in Sailing World, found that depowering to flatten the boat can work better than having the crew exhaust themselves hiking. Reefing is basic enough that US Sailing includes it in the practical skills for its entry-level Basic Keelboat certification.

The depowering controls

Quantum Sails lists the main tools for taking power out of a mainsail:

• Lower the traveler. Quantum says this depowers without adding too much twist. Dave Flynn (Sailing World) says to lower it as heel and weather helm build, and ease the mainsheet too only in very strong puffs.
• Ease the mainsheet. Quantum says easing opens the sail and can reduce heel and weather helm.
• Add backstay. On boats with an adjustable backstay, this bends the mast and flattens the main.
• Tighten the outhaul. This flattens the lower third of the sail.
• Add luff tension. More halyard or cunningham pulls the draft forward and flattens the sail.

What each control does in normal trim is explained on sail trim.

In what order

The sources agree that you flatten first and reef last, though they list the steps a little differently:

When to reef

North Sails puts it simply: when in doubt, reef. Reef early rather than waiting for the gusts to arrive, and shake the reef out if you end up underpowered. Yachting World's experienced contributors give the same advice for night passages, recommending reducing sail before dark (see navigation).

Squalls are the clearest case for reefing early. Robin Urquhart (Sail) cites NOAA's definition of a squall as a sudden wind increase of at least 16 knots, sustained at 22 knots or more for at least a minute. He says the strongest gusts usually arrive before the rain, and advises reefing early and expecting wind at least 50% above the prevailing conditions. For a sense of scale, the UK Met Office Beaufort scale puts Force 6 at 22 to 27 knots, described as a rough sea. Our Beaufort scale tool has the full table.

What a good reef looks like

North Sails describes the principle: part of the mainsail is lowered and the smaller sail is tensioned at a reef tack at the front and a reef clew at the back. A reefed sail should be flat. The load sits on the reef tack and reef clew, and the small reef points along the middle only gather up loose cloth; they are not meant to carry load.

North Sails' guidance rests on a few principles: keep the boat sailing steadily, close-hauled or close-reaching, under the jib while you work; take the load off the main before lowering it; and secure the reef tack before tensioning the clew. Quantum adds one caution: ease the vang before reefing so the boom does not drop. Learn the specific steps for your own boat on the water with an instructor.

Two preparation tips from North Sails: mark the halyard at each reef position so you know how far to lower, and for longer periods reefed, lash the reef clew to the boom as a backup in case the reef line fails.

Weather itself is covered on wind and weather.