How to Reef a Mainsail: A Complete Guide for Sailors

Reefing a mainsail is one of the most important skills for sailors to master. It allows you to reduce the sail area and power of your boat when the wind gets too strong, improving your safety and comfort. Reefing also helps you maintain balance and control of your boat, especially when sailing upwind or in gusty conditions.

But how do you reef a mainsail properly? What are the different methods and techniques? How do you know when to reef and how much to reef? And what are some common mistakes and tips to avoid them?

In this article, we will answer all these questions and more. We will explain the basics of reefing a mainsail, the different types of reefing systems, and the step-by-step process of reefing. 

We will also show you some examples of reefing diagrams, videos, and pictures to help you visualize the process. Finally, we will give you some advice on how to reef efficiently and effectively in various situations.

Whether you are sailing a sloop, a schooner, a catamaran, or any other type of sailboat, this article will help you learn how to reef a mainsail like a pro.

What is Reefing a Mainsail?

Reefing a mainsail is the process of reducing the sail area and power of the main sail by folding or rolling part of it along the boom or the mast. This creates a smaller and flatter sail that is more suitable for sailing in strong winds.

Reefing a mainsail has several benefits for sailing:

• It reduces heeling, which is the angle that the boat leans to one side due to the wind pressure on the sails. Heeling can make sailing uncomfortable, reduce speed and performance, and increase the risk of capsizing.
• It reduces weather helm, which is the tendency of the boat to turn upwind due to the imbalance of forces on the sails. Weather helm can make steering difficult, increase drag and rudder stress, and cause accidental tacks or jibes.
• It reduces sail stress, which is the strain that the wind puts on the sailcloth, stitching, hardware, and rigging. Sail stress can cause premature wear and tear, shape distortion, and sail failure.

Reefing a mainsail also allows you to adjust the center of effort (CE) of your sail plan, which is the point where all the forces of the wind on the sails are balanced. By moving the CE lower and more forward, you can improve the balance and stability of your boat.

Types of Reefing Systems for Mainsails

There are different types of reefing systems for mainsails, each with its own advantages and disadvantages. The most common ones are:

Slab Reefing

Slab reefing, also known as jiffy reefing or single-line reefing, is the simplest and most common method of reefing a mainsail. It involves folding a horizontal section (or slab) of the sail along the boom and securing it with reefing lines or hooks.

Slab reefing requires a mainsail with one or more rows of reef points, which are reinforced holes or grommets along the luff and leech of the sail. Each row corresponds to a different amount of reefing, usually marked as reef 1, reef 2, and so on.

Slab reefing also requires a set of reefing lines or hooks that run from the boom to the reef points. There are different ways to rig these lines or hooks, such as:

• Two-line reefing: This is the most traditional and secure way of slab reefing. It uses two separate lines for each reef, one for the tack point (the forward corner of the sail) and one for the clew point (the aft corner of the sail). The tack line runs from the gooseneck (the joint between the boom and the mast) to the tack point, and the clew line runs from the end of the boom to the clew point. Both lines are led to the cockpit through blocks and clutches for easy adjustment.
• Single-line reefing: This is a simpler and faster way of slab reefing. It uses one line for each reef that runs through both the tack point and the clew point. The line starts from the end of the boom, goes up to the clew point, down to the boom, forward to the tack point, down to the boom, and back to the cockpit. The line is led through blocks, clutches, and cheek blocks for easy adjustment.
• Hook-and-crank reefing: This is an alternative way of slab reefing that uses hooks instead of lines for the tack points. The hooks are attached to a crank mechanism at the gooseneck that can be operated from the cockpit. The hooks can be engaged or disengaged by turning the crank, which raises or lowers them to match the reef points. The clew points are still secured with lines as in two-line or single-line reefing.

Slab reefing has several advantages:

• It is simple, reliable, and easy to maintain.
• It allows precise control over the amount and shape of reefing.
• It preserves the aerodynamics and performance of the sail.
• It works well with full-batten or partial-batten mainsails.

Slab reefing also has some disadvantages:

• It can be difficult and time-consuming to do in strong winds or rough seas.
• It can create loose sailcloth that needs to be tied or secured to prevent flapping or snagging.
• It can cause chafe or wear on the sail, the lines, and the hardware.

Here is an example of a video tutorial on reefing a mainsail with slab reefing:

In-Boom Reefing

In-boom reefing, also known as boom furling, is a modern method of reefing a mainsail that involves rolling the sail around a rotating mandrel inside the boom. It is similar to roller furling for headsails but applied to the mainsail.

In-boom reefing requires a specially designed boom with a hollow core that can accommodate the mandrel and the sail. It also requires a mainsail with no battens or with vertical battens that can bend around the mandrel.

In-boom reefing also requires a set of lines and hardware that control the rotation of the mandrel and the tension of the sail. These include:

• A furling line that runs from the end of the boom to the cockpit through blocks and clutches. This line is used to roll the sail around the mandrel by pulling or easing it.
• An outhaul line that runs from the clew point of the sail to the cockpit through blocks and clutches. This line is used to tension the sail along the boom by pulling or easing it.
• A topping lift that runs from the end of the boom to the masthead and back to the cockpit through blocks and clutches. This line is used to support the weight of the boom and adjust its height by pulling or easing it.

In-boom reefing has several advantages:

• It is convenient, fast, and easy to do from the cockpit.
• It allows infinite adjustment of the sail area and power.
• It eliminates loose sailcloth and reduces chafe and wear.
• It works well with roachy or square-top mainsails.

In-boom reefing also has some disadvantages:

• It is expensive, complex, and heavy.
• It requires careful alignment and coordination of the lines and hardware.
• It can compromise the sail shape and performance, especially when partially furled.
• It can jam or malfunction if the sail is not furled evenly or tightly.

Here is an example of a video tutorial on reefing a mainsail with in-boom reefing:

In-Mast Reefing

In-mast reefing, also known as mast furling, is another modern method of reefing a mainsail that involves rolling the sail around a rotating mandrel inside the mast. It is similar to in-boom reefing but applied to the mast instead of the boom.

In-mast reefing requires a specially designed mast with a hollow core that can accommodate the mandrel and the sail. It also requires a mainsail with no battens or with vertical battens that can bend around the mandrel.

In-mast reefing also requires a set of lines and hardware that control the rotation of the mandrel and the tension of the sail. These include:

• A furling line that runs from the base of the mast to the cockpit through blocks and clutches. This line is used to roll the sail around the mandrel by pulling or easing it.
• A main halyard that runs from the head of the sail to the masthead and back to the cockpit through blocks and clutches. This line is used to hoist or lower the sail by pulling or easing it.
• A topping lift that runs from the end of the boom to the masthead and back to the cockpit through blocks and clutches. This line is used to support the weight of the boom and adjust its height by pulling or easing it.

In-mast reefing has several advantages:

• It is convenient, fast, and easy to do from the cockpit.
• It allows infinite adjustment of the sail area and power.
• It eliminates loose sailcloth and reduces chafe and wear.
• It works well with roachy or square-top mainsails.

In-mast reefing also has some disadvantages:

• It is expensive, complex, and heavy.
• It requires careful alignment and coordination of the lines and hardware.
• It can compromise the sail shape and performance, especially when partially furled.
• It can jam or malfunction if the sail is not furled evenly or tightly.

Here is an example of a video tutorial on reefing a mainsail with in-mast reefing:

Furling Reefing

Furling reefing, also known as roller reefing, is an older method of reefing a mainsail that involves rolling the sail around the boom. It is similar to in-boom reefing, but without a mandrel inside the boom.

Furling reefing requires a specially designed boom with a rotating mechanism that can wrap the sail around it. It also requires a mainsail with no battens or with horizontal battens that can roll around the boom.

Furling reefing also requires a set of lines and hardware that control the rotation of the boom and the tension of the sail. These include:

• A furling line that runs from the end of the boom to the cockpit through blocks and clutches. This line is used to roll the sail around the boom by pulling or easing it.
• A main halyard that runs from the head of the sail to the masthead and back to the cockpit through blocks and clutches. This line is used to hoist or lower the sail by pulling or easing it.
• A topping lift that runs from the end of the boom to the masthead and back to the cockpit through blocks and clutches. This line is used to support the weight of the boom and adjust its height by pulling or easing it.

Furling reefing has some advantages:

• It is simple, reliable, and easy to maintain.
• It allows some adjustment of the sail area and power.
• It eliminates loose sailcloth and reduces chafe and wear.

Furling reefing also has some disadvantages:

• It is outdated, inefficient, and rare.
• It requires a lot of effort and time to do from the cockpit or the mast.
• It compromises the sail shape and performance, especially when partially furled.
• It can jam or malfunction if the sail is not furled evenly or tightly.

Here is an example of a video tutorial on reefing a mainsail with furling reefing:

Reefing a Balanced Lug Sail

A balanced lug sail is a type of sail that has its tack point forward of the mast and its yard (the spar that supports the head of the sail) angled down. A balanced lug sail can be used on various types of boats, such as sailing canoes, dinghies, or skiffs.

Reefing a balanced lug sail is the process of reducing the sail area and power of the sail by folding or rolling part of it along the yard and the boom. This creates a smaller and flatter sail that is more suitable for sailing in strong winds.

Reefing a balanced lug sail requires a slab reefing system or a roller reefing system. A slab reefing system is a system that uses reef points on the sail and reef lines on the yard and the boom to secure the folded or rolled part of the sail. A roller reefing system is a system that uses a furling line on the yard to roll up the sail around it.

Reefing a balanced lug sail has several benefits for sailing:

• It reduces heeling, weather helm, and sail stress.
• It allows finite adjustment of the sail area and power.
• It eliminates loose sailcloth and reduces chafe and wear.

Reefing a balanced lug sail also has some disadvantages:

• It can compromise the aerodynamics and performance of the sail.
• It can cause jamming or twisting of the sail around the yard or the boom.
• It can be difficult and dangerous to do in strong winds or rough seas.

Here are some examples of reefing systems for balanced lug sails:

Slab reefing system

This is a system that consists of reef points on the sail and reef lines on the yard and the boom. The reef points are grommets or cringles on each side of the sail that correspond to different levels of reefing. The reef lines are lines that run from the yard to the boom through the reef points. 

To reef the sail, the sailor lowers the halyard and the outhaul, which drops the sail along the yard and the boom. Then, the sailor secures the new tack and clew points of the sail to the yard and the boom using the reef lines. 

To unreef the sail, the sailor releases the reef lines and hoists the halyard and the outhaul.

Roller reefing system

This is a system that consists of a furling line in the yard. The furling line is a line that runs from one end of the yard to the other and back to the cockpit through blocks and clutches. 

To reef the sail, the sailor lowers the halyard and the outhaul, which drops the sail along the yard and the boom. Then, the sailor pulls the furling line, which rotates the yard and rolls up the sail around it. 

To unreef the sail, the sailor eases the furling line, which allows the sail to unfurl from the yard.

Reefing a Hanked-On Sail

A hanked-on sail is a type of headsail that is attached to the forestay with metal or plastic clips called hanks. A hanked-on sail can be a jib, a genoa, a staysail, or any other sail that is set forward of the mast.

Reefing a hanked-on sail is the process of reducing the sail area and power of the sail by rolling or folding part of it around the forestay. This creates a smaller and flatter sail that is more suitable for sailing in strong winds.

Reefing a hanked-on sail requires a roller reefing system or a reefing pennant system. A roller reefing system is a device that allows the forestay to rotate and roll up the sail around it. A reefing pennant system is a line that runs from the tack point of the sail to the deck and back to the cockpit. Both systems allow the sailor to reef the sail from the cockpit without going forward.

Reefing a hanked-on sail has several benefits for sailing:

• It reduces heeling, weather helm, and sail stress.
• It allows infinite adjustment of the sail area and power.
• It eliminates loose sailcloth and reduces chafe and wear.

Reefing a hanked-on sail also has some disadvantages:

• It can compromise the aerodynamics and performance of the sail.
• It can cause jamming or twisting of the sail around the forestay.
• It can be difficult and dangerous to do in strong winds or rough seas.

Here are some examples of reefing systems for hanked-on sails:

Roller reefing system

This is a device that consists of an upper swivel, a lower drum, and a furling line. The upper swivel is attached to the top of the forestay and allows it to rotate. 

The lower drum is attached to the bottom of the forestay and holds the furling line. The furling line runs from the drum to the cockpit through blocks and clutches. 

To reef the sail, the sailor pulls the furling line, which rotates the drum and the forestay and rolls up the sail around it. To unreef the sail, the sailor eases the furling line, which allows the sail to unfurl from the forestay.

Reefing pennant system

This is a line that runs from the tack point of the sail to the deck and back to the cockpit. The line is attached to a snap shackle or a hook at the tack point and is led through a block at the bow and a clutch at the cockpit. 

To reef the sail, the sailor releases the clutch and lowers the line, which drops the tack point of the sail along the forestay. Then, the sailor secures the line to a new tack point on the sail, using a reefing hook or a grommet. 

To unreef the sail, the sailor releases the line from the new tack point and hoists it back to the original tack point.

Here is an example of a video tutorial on reefing a hanked-on sail with a roller reefing system:

How to Reef a Mainsail: Step-by-Step Process

The exact process of reefing a mainsail depends on the type of reefing system you have, but the general steps are similar for all methods. 

Here is a step-by-step guide on how to reef a mainsail:

Prepare for reefing

Before you start reefing, you should make sure that you are ready for it. This means checking the weather forecast, planning your course, organizing your lines, briefing your crew, and wearing your safety gear. 

You should also make sure that your sail is in good condition and that there are no knots, twists, or snags in it.

Ease the main sheet and vang

The first step to reefing is to ease the main sheet and vang. This will cause the mainsail to luff, stabilizing the boat by reducing heel and easing the tension on the mainsail making it easier to drop or roll. 

You should also ease the topping lift if you have one, to allow the boom to move freely.

Lower the main halyard or pull the furling line

This will start to reduce the sail area by dropping or rolling part of the sail along the boom or the mast. The amount of halyard or furling line to release depends on how much you want to reef and how your system is marked or calibrated.

Secure the new tack and clew points

This only applies to slab reefing systems. You need to attach the new tack and clew points of the sail to the boom using reefing lines or hooks. Make sure they are aligned and tight, but not too tight to cause wrinkles or creases on the sail.

Tension the main halyard and outhaul

This will finish reducing the sail area and shape the sail for optimal performance. The amount of halyard and outhaul to pull depends on how much you want to tension and how your system is marked or calibrated.

Trim the main sheet and vang

This will adjust the angle and twist of the sail according to the wind direction and speed. You may need to ease or tighten the main sheet and vang to achieve the desired sail shape and balance.

To reverse the process and shake out a reef, you need to do the opposite steps:

1. Ease the main sheet and vang.
2. Release the tack and clew points (only for slab reefing systems).
3. Hoist the main halyard or ease the furling line.
4. Tension the outhaul (only for in-mast or in-boom reefing systems).
5. Trim the main sheet and vang.

Here is an example of a video tutorial on reefing a mainsail with slab reefing:

When and How Much to Reef a Mainsail

The timing and amount of reefing depend on various factors, such as the boat design, the sail inventory, the wind speed and direction, the sea state, and the crew experience. 

There is no definitive answer to when and how much to reef, but there are some general guidelines and tips to follow:

Reef before you need to

This is the golden rule of reefing. It is better to reef early and be prepared for stronger winds than to reef late and be overpowered and out of control. Reefing early also preserves the sail’s shape and performance, as well as the sail’s life and durability.

Reef according to the apparent wind speed

The apparent wind speed is the wind speed that you feel on the boat, which is a combination of the true wind speed (the wind speed relative to the land) and the boat speed. 

The apparent wind speed is what affects your sail power and heeling, so you should reef based on that rather than the true wind speed. 

For example, if you are sailing upwind at 15 knots of true wind speed, your apparent wind speed may be around 20 knots, so you should reef accordingly.

Reef according to your boat and sail characteristics

Different boats and sails have different tolerances and preferences for wind speed and angle. Some boats may heel more or less than others in the same wind conditions, depending on their hull shape, keel type, weight distribution, etc. 

Some sails may have more or less roach, battens, twists, etc., that affect their power and shape. You should know your boat and sail characteristics and reef accordingly.

Reef according to your comfort and safety level 

Ultimately, reefing is a matter of personal preference and judgment. Some sailors may enjoy sailing with more power and heel than others, depending on their skill level, experience, confidence, etc. 

You should reef according to what makes you feel comfortable and safe on your boat, without compromising your performance or stability.

Here are some examples of when and how much to reef a mainsail for different types of boats:

Reefing a schooner

A schooner is a type of sailboat with two or more masts, with the aft mast (the main mast) being taller than the forward mast (the foremast). 

A schooner usually has a gaff-rigged mainsail and a Marconi-rigged foresail, both with slab reefing systems. A schooner can reef either the mainsail or the foresail, or both, depending on the wind conditions and the balance of the boat. 

A general rule of thumb is to reef the foresail first, as it is more forward and affects the weather helm more. 

Then, reef the mainsail as needed to reduce heeling and power. 

For example, in 15 knots of wind, you may want to reef the foresail to the first reef point, and in 20 knots of wind, you may want to reef both the foresail and the mainsail to the first reef point.

Reefing a Schock Harbor 20 sailboat

A Schock Harbor 20 is a type of sailboat with a single mast and a Marconi-rigged mainsail with a slab reefing system. It also has a self-tacking jib with a roller furling system. 

A Schock Harbor 20 can reef either the mainsail or the jib, or both, depending on the wind conditions and the balance of the boat. 

A general rule of thumb is to reef the jib first, as it is easier and faster to do with roller furling. 

Then, reef the mainsail as needed to reduce heeling and power.

For example, in 15 knots of wind, you may want to furl the jib to about 80% of its area, and in 20 knots of wind, you may want to furl the jib to about 50% of its area and reef the mainsail to the first reef point.

Common Mistakes and Tips for Reefing a Mainsail

Reefing a mainsail can be challenging and intimidating for some sailors, especially in adverse conditions. However, with some practice and preparation, it can be done smoothly and safely. 

Here are some common mistakes and tips for reefing a mainsail:

Keep your lines organized and labeled

One of the main causes of reefing problems is tangled or misidentified lines. Make sure your reefing lines are neatly coiled and stowed when not in use, and clearly marked or color-coded for easy identification. 

Avoid crossing or twisting your lines when running them through blocks or clutches.

Practice your reefing routine in calm conditions

Reefing is not something you want to learn on the fly when the wind is howling and the waves are crashing. Take some time to practice your reefing routine in calm conditions, with your crew, or by yourself. 

Go through each step slowly and carefully, and make sure you understand how your system works. Repeat until you feel confident and comfortable with reefing.

Check the weather forecast and plan ahead

Reefing is easier and safer when you anticipate the wind changes and prepare accordingly. Check the weather forecast before you go sailing, and keep an eye on the wind speed and direction while you are sailing. 

If you see signs of increasing wind, such as dark clouds, whitecaps, or gusts, plan to reef before it gets too strong.

Use reefing marks on your halyard and outhaul

One of the challenges of reefing is knowing how much to lower or tension your halyard and outhaul to achieve the desired amount of reefing. 

A simple solution is to use reefing marks on your lines, which are colored tapes or knots that indicate the optimal position for each reef point. 

For example, you can mark your halyard with red tape for the first reef, blue tape for the second reef, and green tape for the third reef. Then, when you reef, you just lower or hoist your halyard until the corresponding tape reaches the clutch or the mast.

Avoid over-tensioning or under-tensioning your sail

Another challenge of reefing is finding the right balance between too much and too little tension on your sail. 

Too much tension can cause wrinkles or creases on your sail, which reduce its aerodynamics and performance. 

Too little tension can cause sagging or flapping on your sail, which increases its drag and wear. 

The ideal tension is when your sail is smooth and flat, but not too tight or too loose. You can adjust your tension by pulling or easing your halyard, outhaul, main sheet, and vang until you find the sweet spot.

Use a reef knot to secure the reef points

A final challenge of reefing is securing the loose sailcloth that remains after reefing. This is especially important for slab reefing systems, where the sailcloth can flap or snag if not tied or secured properly. 

The best way to secure the sailcloth is to use a reef knot, which is a simple and secure knot that can be easily tied and untied. To tie a reef knot, you need two lines that run from the boom to the reef points on each side of the sail. 

Then, you cross the lines over each other, twist them once, cross them again, and pull them tight. You can also use a buntline or a buntline hitch to secure the sailcloth.

Here is an example of a video tutorial on how to tie a reef knot:

FAQs

Here are some frequently asked questions and answers about reefing a mainsail: