Simple Reefing System for Sailors

Yacht sailing on the ocean
Southern Ocean, Australia. John White Photos / Getty Images

Reefing the mainsail involves lowering the sail part way to reduce its size when the wind increases. A reefed sail reduces heeling of the boat and makes the boat easier to manage. It also reduces the risk of capsizing in a gust. Reefing the mainsail is like partly furling the jib when your boat has a furling jib.

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Why and How to Reef the Mainsail

Mainsail reefing

Tom Lochhaas

The classic sailor’s saying is that if you are asking whether it’s time to reef the main, it’s already past that time. This refers to sailors who are having difficulty controlling a wildly heeling boat because the wind has gotten up and is putting a lot of pressure on too much sail area.

A prudent sailor reefs the main when the wind starts to build before things get wild. When the wind is blowing more than twelve to fifteen knots, depending on the boat, conservative sailors will start out with a reefed sail. Over twenty knots on many boats and it can become difficult to control the boat for smooth reefing, especially when short-handed.

When you’re sailing downwind and the boat is not heeling, you may not notice at first that the wind is increasing. Since you have to turn up into the wind to do the reefing, things may get dicey if you wait too long to reef.

How to Reef

With the common slab reefing system, reefing is fairly simple, though it’s a skill that requires some practice. The basic steps are:

  1. Turn the boat toward the wind and ease the mainsheet to reduce pressure on the sail.
  2. While slowly easing the main halyard, take in the reefing control line. This pulls the bottom of the mainsail down toward the boom.
  3. When the sail reaches the desired reef point, secure the halyard and the reefing line, go back on course, and trim the sail.
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Slab Reefing System

Single-line slab reefing system illustration

International Marine

This is a simple slab reefing system you can easily install on your boat if you do not have one. If you already have a reefing system, be sure you understand how it works before you need it in rough conditions.

The illustration shows a single-line system. Larger boats often have a double-line system, in which a second reefing line is added on the other side of the boom to the second higher set of reef points. There are also variations in the use of a hook, or reefing horn, at the forward reefing point on the sail’s luff.

How the Reefing Line Runs

  • From a fixed point on the port side of the boom, the line rises to the aft grommet in the sail, called a reefing cringle.
  • The line continues down the sail on the starboard side to a turning block mounted on the boom, then forward along the boom to another turning block.
  • The line rises up to the cringle on the sail’s luff edge. In the illustration, the line passes through a block on a reefing horn and then back down. Alternatively, the line may pass through the cringle and down on the port side in the same manner as it did through the luff cringle. The advantage of the horn with a block is reduced friction, and the horn can be raised to a higher reef point as well. The disadvantage is that a crew has to go forward to position the horn.
  • Finally, the line comes down to a turning block at the base of the mast and back to the cockpit, where it can be taken in for reefing.
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A Reefed Mainsail

Reefing mainsail

Tom Lochhaas 

A reefed sail using a slab reefing system is illustrated in the photo shown. On this boat, the reefing line runs through the cringle at the sail’s luff rather than using a horn. The position of the aft turning block on the boom is a little back from the cringle when the sail is reefed. This helps keep the sail taut for better trimming when reefed.

The Second Reef In

This mainsail has the second reef in. If you look carefully at the leach of the sail where it lies against the boom, you can see the cringle of the first lower reef point.

Depending on the conditions, a boat with two reef points and a double-line system allows you to reef the mainsail in stages from the first to the second reefs. You can also go all at once to the second reef if needed.

This boat has lazy jacks in place that help hold the lowered part of the sail on the boom. No additional securing may be needed. Without lazy jacks, the bottom of the sail can blow about and get in the way.

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Tie Up the Reefed Sail

Reefing mainsail tied up

Tom Lochhaas 

Most sails with reefing cringles also have smaller grommets across the width of the sail at the same level as the reef points. After reefing, you can secure the loose part of the sail to the boom by passing a sail tie through the grommets and tying it off around the boom, as shown here. It’s not a coincidence that the best knot used here to tie the reef in place is called a reefing knot.

Some sailors prefer not to tie off the reefed main at these smaller grommets because of the risk of forgetting them later when you shake out and remove the reef. If you loosened the reefing line and started raising the mainsail back up without first removing these ties, the mainsail may rip.

To Shake Out a Reef

To remove the reef and raise the mainsail back up, simply reverse the basic reefing steps:

  1. Turn the boat toward the wind and ease the mainsheet to reduce pressure on the sail.
  2. While slowly easing the reefing line, pull in the halyard to raise the mainsail back up.
  3. When the sail is fully up, secure the halyard and the reefing line, go back on course and trim the sail.

Other Reefing Systems

With larger cruising sailboats, manufacturers are increasingly offering in-boom and in-mast reefing and furling systems for mainsails. Such systems essentially involve a roller inside the boom or mast with an electric motor that rolls up the sail to reduce its size (reefing) or to stow the sail away after sailing. While such systems certainly add convenience when they’re adjusted and everything is working well, many experienced sailors still prefer slab reefing, which doesn’t depend on an electrical system, multiple moving parts, and a fine-tuned rig.

Slab reefing does require some practice and careful installation of the basic system. Once the line is rigged, it’s always ready for use and comes close to being foolproof.

Monitor changes in the wind so that you can reef early when it's easy, rather than late when it's difficult or dangerous. You can learn to read the wind or use an inexpensive handheld wind meter. Additionally, you can use the traveler and other sail adjustments for strong winds.