How to Reef the Mainsail (Slab Reefing) — and Shake it Out Again
As a new sailor, learning how to reduce sail area (reefing) is one of the most important skills you can develop. When the wind picks up, reefing the mainsail helps maintain control, comfort, and safety. Slab reefing (also called jiffy reefing) is a common system and is straightforward once you’ve practiced the steps.
Reefing the Mainsail
Reef before you need to. If you’re thinking about reefing, it’s probably already time.
- Brief the Crew – Ensure everyone aboard knows what’s about to happen and what their role is — especially the helmsperson and anyone handling lines.
- Head into the Wind – Steer the boat into the wind (the “no-go zone”) to depower the sail. This keeps things calm and manageable.
- Ease the Mainsheet and Vang – Let the mainsheet and boom vang off completely. This allows the boom to rise and the sail to fall freely.
- Tighten the Topping Lift – Pull the topping lift on to support the boom and prevent it from dropping as the sail is lowered.
- Lower the Main Halyard – Ease the halyard until the sail drops to the appropriate reef point — this is usually marked on the halyard or mast.
- Secure the Reef Tack (Luff) – Hook the reef tack (the forward reef cringle) onto the reefing horn (“bullhorns”) or attach it using the designated lashing/hook at the gooseneck. Make sure it’s secure.
- Re-Tension the Halyard – Hoist the halyard again, using a winch if needed, until the luff is firm. This prevents horizontal creases and keeps the sail driving efficiently.
- Tension the Reefing Line (Clew) – Pull in the reefing line attached to the clew (aft corner of the reef). This brings the new clew down to the boom and tensions the foot of the sail. Use a winch or good hand tension as needed.
- Trim and Rebalance – Ease the topping lift (if required — some boats leave it on). Re-tension the boom vang. Trim the mainsheet to suit the course. Return to your desired point of sail.
Shaking Out the Reef
As conditions ease and you’re looking for more drive, it’s time to return the mainsail to its full area.
- Assess Conditions – Make sure it’s safe to shake out the reef — steady lighter breeze, no gusty surprises.
- Luff Up into the Wind – Steer into the wind again to depower the sail and make handling easier.
- Ease the Mainsheet, Vang and possibly the outhaul – Let off these controls completely so there’s no load on the sail.
- Release the Reefing Line (Clew) – Let go the reefing line that was holding the reefed clew to the boom. Flake the line neatly to avoid tangles later.
- Ease the Main Halyard Slightly – Lower the halyard just enough to take the load off the luff, so you can unhook or unlash the reef tack from the horns/gooseneck.
- Hoist the Mainsail to Full Height – Raise the halyard all the way to the headboard stop. Winch up if needed and make sure there’s good luff tension.
- Re-tension and Trim – Adjust the outhaul and vang for full-sail trim. Trim the mainsheet and return to your course.
- Stow Lines – Coil and secure the reefing lines and halyard tail. Tidy decks are safe decks.
With a little practice, reefing becomes second nature. The goal isn’t just to keep the boat upright — it’s to keep it balanced, comfortable, and under control so you can enjoy the sail and get to where you want to go efficiently.
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