Reefing Part 1 of 4

Reefing: Issues, Techniques, Systems and Solutions

A White Paper, the first of four, discussing why reefing is necessary, the three most common techniques and their benefits and disadvantages.                                     

Reefing is one of those activities on a boat that most of us like to avoid. Regrettably, not all sailing is conducted on balmy days with warm sun smiling down on us and flat water. Once in a while, we do need to get from A to B, upwind in 25 knots. Like everything else on boats, nay, in life, in fact, an understanding of ALL the aspects of the task and the odd bit of practice goes a long way to making The Task less onerous. Let me set up the discussion with some background on The Philosophy and Principles of Reefing.


A sailing boat is impacted by the force vectors created by wind, sea state and boat speed. There are eight inputs that determine how a boat ‘feels’ that is, if it is easy to steer, is not knocked down in gusts, and ‘feels’ good on the helm. These inputs are: true wind speed and direction, apparent wind speed and angle, boat speed and pitch, roll and yaw. These forces are resolved by sail trim, correct sail size and shape and steering to arrive at the proper balance of the boat. The ‘answers’ to these force vectors are ‘sent’ to the helmsman via the rudder to the tiller or wheel. WHEN the boat is overpowered, well we all know what that feels like and can determine it pretty easily.

Reefing is one aspect of the ‘correct sail size and trim’-Remember when a mainsail is reefed, it certainly gets smaller in area but what is often not addressed is the make it flatter part of the equation-We will get to this in a minute.

As for taking a reef, or shaking it out for that matter, this task is at that point where ‘sailing’ intersects with ‘seamanship’. The former is sail trim & steering, the ‘normal’ activities of steering the boat. Seamanship is all the activities one must be proficient in that are not actually steering or trimming. Anchoring, navigation, sailing, or motoring up to the dock or mooring, changing sails and so on are, of course, an intimate part of sailing but are not, of themselves, sailing.

We have all been aboard a boat, maybe our own boat, when she is heeling too much, where the leeward rail is in the water and may be getting into the cockpit, waves are breaking across the bow sending water over everyone, she is hard to steer, the sails are flapping, there is a lot of noise, and the whole situation is stressful. Ring a bell?

Any one or multiples of these events are among the key indicators that something needs to change.

WHY WE NEED TO REEF, the numbers

The reason for the need to reef is driven by the physics, the technical aspects of the sails: their size and shape and wind speed. The starting is this:

The wind FORCE increases with the square of the wind SPEED. At 12 knots of wind, there is 144 psi on the sails; BUT at 15 knots of wind, there is 225 psi on the sails. So for a 25% increase wind SPEED, there is a 56% increase in FORCE.

At the wind speeds where we are thinking about reefing, around 20 knots apparent, there is 400 PSI versus the 225 at 15 knots which is a 77% increase in FORCE, on an increase in wind speed of only 33%.

Secondly, as the wind SPEED increases, the DRAG increases, at the same rate. Unless the sails are made flatter, as the wind speed increases, there will be more drag. This is why the progressively smaller jibs are progressively flatter. Another comparison I draw here is the difference in wing shapes between a 747 airliner and an F-14 fighter jet.

The 747 Jumbo Jet is heavy and does not fly fast relative to the F-14, so the air (the apparent wind speed in a sailing boat, too) flowing over the wings is less than an F-14. The Jumbo needs lots of lift, so the wings are big in area, and thick, like full sails. The F-14, on the other hand, has loads of power, flies really fast, and so, has lots of ‘apparent wind’ and is looking to reduce drag so the wings (sails) are small and ‘flat’ like a number three or four jib.

Back to sails: In light to medium air, a sailboat is looking for power, (Think: a Jumbo on take off from FLA in winter, full of people, baggage and fuel) so the sails (wings) are full. When the wind speed increases, as when the plane speeds up and the forces increase, on a sail that is now too full, the DRAG on the sail (wing) increases. This increase in drag, on the sails, is felt through the wheel or tiller and manifests itself as being ‘heavy’, or weather helm resulting in the increasing difficulty in steering, described above.

This is one of the reasons why, if you are sailing in August in San Francisco Bay, your sails will likely be smaller and flatter than if you sail in Long Island Sound in August.

The foregoing list is not at all conducive to happy sailing but can be greatly improved upon by reefing, and so making the boat more manageable and docile and more comfortable and less stressful for all concerned.


Let’s take a look at this discussion for an actual boat, in this case a 1980’s Pearson 40. I produced a version of the following table for a fellow we are working with in preparation for his sailing in the 2019 Bermuda 1-2. The question to answer was ‘what was the optimal size of the mainsail at each reef?’ His main will have three reefs. A secondary reason for this exercise was to get data related to changing his mainsail sheeting system. The chart was prepared using calculations of mainsail force from the Harken website. This calculator is designed to estimate the loads for sizing a block, but it works well for this exercise too.

The salient point to follow on this chart is the amount of force, the load, on the sail at full hoist and at the first, second and third reefs. The goal of reefing is to maintain a force, or load, on the sail that is similar to that load in the sail at full hoist at between 18 and 22 knots apparent. This wind speed is, generally speaking, the amount of apparent wind in which this kind of boat will be at full speed, with the full size genoa set, sailing fully trimmed, upwind, as though (not necessarily) racing-I.E. tying to maximize upwind VMG.

There are some variables not addressed:

  1. Whether or not the boat has a smaller headsail that a 150.
  2. If the mainsail AND the mast and rigging are constructed, installed and operated in a way to make large adjustments in the mainsail shape.
  3. Strategic and tactical issues (when racing) to do with the weather on the sailing area: Some areas have conditions of wide variations in wind speed and direction. Long Island Sound in a north westerly is like this so, when ‘racing’ the sail combination is calibrated for the average, or lower winds and the upper wind speeds, in the gusts the sail trim is adjusted where possible since the puffs are often short lived.
  4. If the boat is being sailed with lots of crew on the rail or, as in the case of the fellow for whom this information was prepared, sailing alone without the stability and power provided by crew sitting on the rail.
  5. The sea state.


The column headings (Line 0) in BLUE are for full hoist and 1,2 and 3 reefs. As we progress with this exercise, we will follow the columns down to the load on the sail at each apparent wind speed, represented under the column heading of the same name, at line 7.

A second aspect to this exercise was to determine the loading on the mainsheet at various wind speed and reefed combinations. The reason for this being we are looking at ways to modify the mainsheet system so he can adjust it from the helm area rather than it’s present location on the cabin top-A not uncommon location for boats of this vintage. We were looking for the sheet loads in worst-case situations. The sheet is presently 5:1 onto a winch. The original calculations I did for the client had a calculation for 6:1 and 24:1-This latter ratio was to be gained by having a 4:1 fine tune on the 6:1 coarse adjustment for a total of 24:1 Basically, like most of the 30-36 foot J boats.

The point here is to determine the loads at each reef at wind speeds up to 50 knots apparent-line 27, which is roughly about 43, 45 knots true wind speed for most boats in this size range. I arrived at the areas by marking the luff height on the sail plan and then extending this across the sail to the clew reef position, noting the distance and using the new shorter luff and foot to arrive at the sail areas entered across line one.

Read Line 1, across. This presents the area in sq. ft. of each reef, subtracted from the full hoist area (352 sq. ft.) For example with first reef in the sail area is down to 280 sq. ft. from 352 sq. ft.

Read Line 2, across. This is the amount of area by which each reef reduces sail area from the FULL HOIST sail, i.e. 72, 119 and 192 sq. ft.

Read Line 3, across. This is the amount of area by which each reef reduces sail area from the PREVIOUS REEF, 47 and 73 sq. ft.

Read Line 4, across. This is the amount of area expressed as a percent by which EACH REEF REDUCES SAIL AREA from the full hoist sail, 26, 34 and 45 percent. In other words with the third reef in the sail area is reduced by 45 percent.

Read Line 5, across. This is the amount of area, expressed as a percentage by which each reef reduces sail area from the PREVIOUS REEF, so 20, 35 and 38 percent.

You may read for yourselves the loads at each two-knot increase of apparent wind speed. The salient ones I highlighted are for the loads for full hoist at line 11-18Kts. and at line 14-24Kts.  At 18 kts apparent, the load is 1,279 lbs. and divided by 5 (The mainsheet system is presently 5:1 led to a winch) the load at the winch is 256 lbs. In the event we did go to the 24:1 system, the load on the fine tune would be only 53 pounds, (1,279lbs. /24 [to 1]) a load readily adjustable by hand-which was the point.

At line 14, the apparent is 24 knots the load is up to 2,274 pounds. This represents a 33% increase in wind SPEED, but a 77% increase in the FORCE. Get the picture now? And the 24:1 mainsheet system is up to about 95 lbs. more load but well within the scope of someone sailing a 40 footer by themselves.

If you study this table, you will see that in the reefed columns I have highlighted forces that are similar to the force at between 18 and 24 knots apparent with a full hoist. I used these wind speeds as a baseline because it is in this range that the boat, most boats of this general style and size will be at the upper limit of their ability to carry sail. This is the wind speed and conditions where the boat is heeling too much, the helm is heavy, spray is flying, the sails are flapping and so on.

With the first reef at between 22 and 28 knots apparent with loads of 1,424 to 2,307 lbs. are in the same area as 18 apparent at full hoist. And remember this discussion does not take into account changes in the headsail area or any of the other variables noted above.

With the second reef, the wind range to shadow this force is between 26 apparent up to 30 apparent. And for the third reef, you are at between 36 and 40 apparent.

And so it goes, you can study this table and consider what the loads are on your boat.


Fig 1: An open 60 heavily reefed off New Zealand

Fig 2: This Quest 30, a sporty boat with a bigger than average sail plan for a 30-foot boat is very often reefed in comparatively low wind speeds.










A review of the foregoing

Flat is fast

1) When you reef the sails need to get flatter, as well as smaller. This is one of the most commonly neglected aspects of the whole reefing process. So, how do we get the sails flat as well as small?  The most important part of this is the make sure the clew of the sail can be tensioned, easily and effectively and that the new foot’ of the al can be made tight, so the sail becomes flat. Equally important is getting the correct firm tension on the luff.

Fig. 3 The ability to pull the leech reef aft is critical to effective-FLAT- sail shape

Now let’s have a look at the various ‘systems’ used for reefing, excusing from the discussion, in-boom furling and in, or behind, mast furling.

How DOES one reef, (properly)?

1) The blocks, sheaves, leads, string and clutches.

There are three principal ways to rig the reefing system. These three ways, or ‘systems’ vary by the age, style, most common use of and size of the boat. Generally speaking, most production boats employ (sailing) systems and techniques taken from the race boats designed a few years prior to the introduction of the production boat. There are three basic versions of the ‘systems’ that boats have. By ‘system’ I am thinking of the path the reefing lines (and halyard) take including blocks, fair leads, snap shackles, hooks, clutches etc. that are necessary to effectively tuck in a reef. There are a few small variations I will get to.

2) How do you like to sail?

As odd as it seems, how you prefer to, or like to, or will, sail the boat has a big impact on all things reefing. Things like your age, or more accurately your level of physical fitness, agility and strength, your willingness to move around the boat in conditions under which reefing is necessary-In particular when setting the second or third reef. Experience in general terms and with this particular boat. Familiarity with the boat and its systems, and if you are racing, how much practice the crew has had reefing are all elements that will impact the reefing process and so largely dictate the way your boat is rigged, or can be re-rigged, to make reefing most seamanlike.

4) How long does it take to reef? As quickly as can be done…

There are a multitude of variables here and in no particular order some are:

  1. How many times have you reefed this boat prior? The more you do it, regularly, the easier and faster it will become-It is perfectly acceptable to practice reefing every other time you go out…
  2. The efficiency, read minimal friction, of the system-more friction means more energy to trim lines in, wind winches and this means the humans are getting worn-out faster.
  3. The distance one needs to travel on the boat to affect a reef…do you need to go to the mast or is it all done from the cockpit? This is connected to sea state too.
  4. On what point of sail are we trying to reef? Reefing is easier upwind than across the wind or down wind, largely because when across or down wind there is much more friction from the sail laying across the lee rigging. This is aggravated sometimes quite dramatically, if the mainsail has full-length battens without any low friction sliders or cars at the luff so the slipperiness (friction, or lack of) factor of the slides on the main plays a role too.
  5. Related to this detail is the mast and standing rigging configuration. On more modern boats, say from 2000, and any boat where the spreaders are swept aft, from a J-30 all the way to the latest European boats, this configuration contributes to the increased drag on the sail as it goes up or down, when sailing across or downwind because the sail is now dragging across the standing rigging and spreaders.
  6. The amount of friction, or lack of it, across the entire system is also a big factor. Sheaves in the boom corroded and not turning freely or reefing line that are too thick for the blocks are two very common problems that, if fixed, will make reefing, if not perfect, less cumbersome and slow.
  7. And how well prepared the reefing system is particularly with respect to marks on the various lines making it easier to place a line where you know it needs to go and moving onto the next step.
  8. It is, in my opinion, perfectly possible to reef a regular 40 foot boat in less than a minute with the right system, set up the right way, well prepared and carried out in the right sequence. A bit longer across or downwind.

The steps required to reef are:

  1. Decide you need to reef
  2. Announce this to the crew and make sure they are awake and stationed where then need to be. Have them wait for the command, not simply just start in on their own task as soon as they arrive at that position.
  3. Make sure the various lines are clear to run, especially the halyard, that the crew knows which line is to be handled in what order, that there are winch handles located close to hand as needed and so on. Magic marker marks on the halyard or a few turns of seizing line with the tail sticking out makes it easier to feel as well as see.
  4. Ease the sheet, enough. This is the amount necessary to take the load off the sail such that it is luffing to, at a minimum, ¾ of the way aft from the luff of the sail. From here, it is a fine-tuning exercise each time you reef.
  5. The person steering plays a role too, maintaining a steady course based on the apparent wind angle, with the mainsail now (quite) eased. The balance, and so the feel on the boat, will be different than when the mainsail was trimmed in and the boat was more or less balanced. A common steering problem is when the mainsheet is eased the wheel, the helm goes light so the person steering bears down to get feel back into the helm and the boat tends up reaching instead of being close hauled. For instance
  6. Ease the vang, enough, and if you have a topping lift and not a rigid vang, trim the topping lift to a pre-determined point. This point is that which lifts the boom, ‘just a bit’, i.e. sufficient to take the weight off the boom and the leech of the sail. The reason for this is that almost universally sail makers will place the reef rings progressively higher up the leech, say 2,3 inches on an average 35-50 foot boat. This is so the successive reefs do not need to be jammed into the boom, on top of the already fabric-filled area. So the leech reef ring can be a few inches away from the boom, and still the boom is more or less horizontal.
  7. Lower the main halyard-and this is where the variations start to kick in-Lower the halyard to, ideally a previously determined point. As part of the discussion on Seamanship, preparation, that is testing this stuff at the dock, is a key ingredient here.
  8. Secure the tack of the reef point —THEN
  9. Tension halyard (this is ALWAYS to be completed before tensioning the leech reef line.)
  10. Tension the leech reef line. (It is critical in the arrangement of the leech reef line that the ‘new’ foot of the sail can be pulled aft and tensioned in order to make the sail flat.)
  11. Release the topping lift, letting the load come back into the sail-Otherwise you will end up trimming the mainsheet against the topping lift and not the sail. This helps to not break the topping lift too.
  12. Trim the sheet and vang as appropriate
  13. Secure the bunt (the bit of sail fabric now flapping between the boom and the reef point), as you feel necessary
  14. Check for chafe, and regularly there after.
  15. Put on the kettle for tea.

If you are at sea AND the conditions seem to be settling in for the duration, rig up some back up lines. I will get to these later on.

The foregoing is roughly the sequential narrative of reefing. The nuances depend on which of the three systems you have.

I will discuss these three systems individually in subsequent posts.