Sailing Guide‎ > ‎


Reefing the mainsail involves lowering the sail partway 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.


When to Reef

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 12-15 knots (depending on the boat), conservative sailors will start out with a reefed sail. Over 20 knots on many boats, it can become difficult to control the boat for smooth reefing, especially when short-handed.

Remember that when you’re sailing downwind and the boat is not heeling, you may not notice at first that the wind is increasing. Pay attention! 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:

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


Shown here 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.

This 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.

Here’s how the reefing line runs:

  • From a fixed point on the port side of the boom (not seen here) 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 this 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.


This photo shows a reefed sail using a slab reefing system. On this boat the reefing line runs through the cringle at the sail’s luff rather than using a horn. Note also that 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.

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

Note also that 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. But without lazy jacks, the bottom of the sail can blow about and get in the way. Go to the next page to see how to secure it.


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 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 (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:

  • Turn the boat toward the wind and ease the mainsheet to reduce pressure on the sail.
  • While slowly easing the reefing line, pull in the halyard to raise the mainsail back up.
  • 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/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, but once the line is rigged, it’s always ready for use and comes close to being foolproof according to the KISS principle (“Keep it simple, stupid!”).

Slab reefing, also known as "jiffy reefing," is a process of temporarily removing sail area from the main by lowering the halyard and re-fastening the boom to the sail using reinforcements sewn to the sail at the reef tack and reef clew.


By developing the skill to properly reef your mainsail you will lengthen the life span of your sail (by flogging it less), have fewer repairs done to the sail (by not tearing it), and reduce the emotional stress on those sailing with you...and probably yourself as well!

The big deal in reefing is making sure that during the reefing process and while the reef is in use, the loads are carried by fittings on the sail which are strong enough to do the job. When considering a reef, the strongest parts of the sail are the headboard, the reef clew, and the reef tack. You can convince yourself of this by closely looking at the size and number of layers used for reinforcements at these areas. The weaker parts of the sail are the luff sliders, and the spur grommets which are used to fasten the sliders to the luff of the sail, as well as the interim reef points used for tying the reefed portion of the sail around the boom. If you look closely at these locations you will notice that there are only two or three layers of cloth where the spur grommet is set.

Now that we know which parts of the sail are supposed to be pulled on, we need to understand what each line is doing to the sail. The halyard is obviously holding the sail up. The reef clew line is trying to pull the sail away from the mast, and the reef tack line is trying to hold the reef tack down and forward. Each of these lines is doing an essential job, drawing the sail taut, each corner pulling away from the others, making the sail flat...not a bad idea on a windy day.

It is important to note that the luff sliders are simply there to guide the sail up and down the mast when the sail is raised or lowered. Individually, each one is intended to support only a relatively small percentage of the sail.

When reefing, the order in which lines are tensioned or eased needs to follow a fairly rigorous procedure. Most importantly: you must not pull on the reef outhaul until you have established vertical tension on the luff between the halyard and the reef tack. Once luff tension is established, the luff sliders are protected from the large load imposed by the reef clew line. The penalty for improper reefing is usually a torn sail.

Practice reefing with the boat at the dock early in the morning when there is no wind. This is the perfect time to get the predetermined marks on the main halyard. When you practice reefing at the dock, you will be able to focus your attention on how things are progressing without any distractions that come with actually sailing.

I describe three types of reefing systems here:

  • two line reefing system, which is I think the simplest to use, fastest to reef and unreef, and possibly the easiest on the sail itself.
  • tack horn or tack hook for reef tack ring, which is easiest for the boat manufacturer to install, and not a bad system, but cumbersome and requires someone go to the mast to get the reef rigged.
  • single line reefing system, which I'm afraid we are less than fond of here at Pineapple Sails (see below).


Generally the reefing operation starts out the same, but changes depending on what type of reefing system you use. The steps are as follows:

  • unload controls which hold boom down
    • boom vang
    • preventer (?!)
    • mainsheet
  • hold boom up if possible
    • trim in topping lift
    • support can also come from a hydraulic or "rigid" vang
  • lower halyard and set reefed luff tension
    • two line reefing system
      • lower halyard to predetermined mark which leaves reef tack a little high
      • tension the luff by trimming in the reef tack line, pulling the reef tack down
    • tack horn or hook for reef tack ring
      • lower the halyard low enough to slip reef tack ring onto horn
      • tension luff by grinding halyard back up
    • single line reefing system
      • lower halyard to predetermined mark
  • trim in the reef clew line until the foot of the sail is flat along the top of the boom
  • release topping lift
  • trim main sheet and vang
  • tie in reef points if desired

If you follow the above guide line, the reef should be installed pretty quickly, and easily too. It should not be necessary to pull tremendously hard on the reef clew line, because all you are doing is tensioning the foot. The leech of the sail will be slack, and if you use the topping lift to hold up the boom, you don't even have to lift the weight of the boom with the reef clew line.


The process for unreefing is essentially the same, but with a twist or two.

  • untie the reef points if you tied them in
  • unload controls which hold boom down
  • ease off the outhaul and/or flattener (NOT THE REEF CLEW LINE!)
  • hold boom up if possible
  • be sure all un-related reef lines are clear to run
  • undo the reef lines
    • two line reefing system
      • ease off the reef clew line
      • ease the reef tack line
      • raise the halyard
    • tack horn or hook for reef tack ring
      • ease off the reef clew line
      • lower the halyard low enough to slip reef tack ring off the horn
      • raise the halyard
    • single line reefing system
      • ease off the single reef line
      • raise the halyard
  • trim on the outhaul/flattener
  • release topping lift
  • trim main sheet and vang

The point of item 3 is that it will be easier to hoist the sail if the sliders are under less load. We accomplish this by slackening control lines which are trying to pull the sail away from the mast. Notice we are NOT talking about the actual reef clew line which is in use at this time, but rather control lines which are "below" the reef clew.


I would like to discuss the single line reefing system as a separate subject. My biggest problem is that one cannot establish luff tension, thereby reducing the load on the luff sliders, before placing a load on the reef clew line. This will often cause the bottom several luff sliders to start tearing out of the luff of the sail. My second problem is that these 'systems' are sold under the notion that they are 'simple.' They are NOT simple. That is partially due to the fact that the loads in a reefed sail are not simple. The load coming out of the reef clew is very much greater than the load out of the reef tack. (If you look closely you will notice that the size of the reef clew patch is greater, and with more layers, than the reef tack patch.) It is difficult to have a single line carry a large load in one end and a small load in another end...not impossible, just difficult (not simple). To get around this, some single line systems do not have a "single line," but rather two separate lines, one is the reef clew line which lives inside the boom with a block attached, and the other, which starts at the front of the boom, travels aft to this block, then forward to the reef tack, then down and aft to the cleat...not simple.


  • Sail shape is important. It is possible/preferable to get a reefed sail to be relatively flat, thereby reducing excess heeling. A common fault is not pulling aft hard enough on the reef clew line. Sometimes the hardware on the boom is anchored too far forward to allow proper flattening of the foot. The lead should be back and down.
  • Luff sliders: You don't want to see wrinkles coming out of these sliders at any time. The wrinkle implies a load which is greater than what the slider was intended to carry. Some of the ways to get these wrinkles are:
    • by pulling on reef clew line before luff tension is established
    • by getting a luff slider stuck in the gate where they are inserted into the tunnel/track
    • by trying to pull the reef tack lower that the sail slide stop will allow the intervening slider to (1) remove the stop and allow the offending slide(s) to come out/off; (2) don't try to place reef tack at the level of the doesn't matter; (3) instal a jack line onto the sail to allow the sliders to migrate away from their 'normal' location, (4) modify the sail slide gate or sail slide track to allow the slides to go all the way to the gooseneck (elegant!)
    • If the reef tack is dragged aft by the load in the reef clew line, then there is a reef tack offset problem. The reef tack line is not holding the sail forward enough. The result will be that a large load will be transferred to the first sail slide above the reef tack. This can be solved on the water by tying a sail tie through the reef tack ring and around the mast, being careful not to trap the halyards.
  • Tearing luff slider off headboard...prevent this by placing the halyard in the aft hole in the headboard, which is a good idea on all windy days, even if not reefed
  • The reef points should not have wrinkles coming out of them. Their job is to hold the excess sail cloth up from hanging below the boom, not to pull down on the sail above the reef. If your reef lines are properly set, tying off these points will have no effect in the shape of the sail above the boom. If the cloth below the boom is "well behaved," (not flogging, not blocking your view, etc.) we recommend that you do not tie in the reef points, because a common repair stems from trying to unreef the main without untying the reef points!
  • If you don't have a way to hold the boom up while reefing, be careful that the boom doesn't get caught under the lifelines.
  • The easiest heading to steer while reefing or unreefing is either a beat (notice a lot of lee helm?!), or a close reach. This will keep the boom out of the cockpit, and away from the heads of you and your crew.
  • From the sails point of view, the hardest heading to be reefed or unreefed is on a run. The problem here is the sail will be pressed against the leeward shrouds and spreaders by the wind. This will add friction and sometimes cause tears as the sail is dragged past the standing rigging. Full length battens make this problem worse, because the batten is acting as a lever with the shroud as a fulcrum, trying to pry the luff slider out of the sail track. The best solution to this problem seems to be to purchase one of fancy mainsail luff slide systems made by Harken, Antal, Ronstan, and others.