Mainsail Reefing.


Here I bang on quite a bit about efficiency, ease of use, etc. and make no apology for doing so. Especially when single or shorthanded things need to work smoothly and easily as you lack the brute force and extra hands you have in a fully crewed boat. A fully crewed racing boat may put up with minor inconveniences for the sake of speed of operation that, when by yourself, at two in the morning could turn into a character building incident.

When equipping and setting the boat up, go for ease of use rather than speed, although the two often go together. Consider what could go wrong and try and design the problems out or have a mitigation / recovery plan thought through in advance.

Particularly when you are sailing shorthanded, reefing systems need to be easy and quick to use, extremely reliable and suitable for the boat and rig, a mainsail reefing system that works well on a mast head rigged 20 foot boat may be a disaster waiting to happen on a larger fractionally rigged boat with a huge mainsail, so choose carefully. 


Self-steering systems working to the apparent wind may have problems when reefing, either because of the change in apparent wind when a sail is depowered or as the boat becomes unbalanced. Only experience will tell if this is significant on a particular boat in any given configuration, if necessary let the boat fall off a little before starting. 

In boom and in mast roller reefing

Hustler 30 reefing.
Popular, particularly on largish boats, and easy to use – although it may require a big or powered winch on some systems.

If you have one of these and it works tolerably well it is unlikely that  you will take it out and if you don’t have one you aren’t going to put one in, as both would be very expensive, probably more than an old or middle aged boat cost. So, it is not worth saying much about them.

Many people like them and I have seen some quite small boats with them, but personally I would avoid both, especially the in-mast system, the thought of having a couple of rolls in and it jamming with a storm coming along is not pleasant, at least with an in boom system you should still be able to get the rest of the sail down.

Round boom roller reefing

The main variant is known as “Through mast roller reefing” because the boom is rotated with a cranking handle on the front of the mast. Back in the 1970s it was very popular on cruising and day boats and was standard equipment on many, including the Achilles series. Other systems, some dating back to the 1930s and earlier were available with different turning mechanisms – through-mast might be tricky with a wooden mast.

1930's 50 square metre "Sperling".
They have gone out of fashion and in my view rightly so, although I know of one owner who swears by his, I used to swear at mine, and I only used it for stowing the sail! OK for day sailing in sheltered waters but in my opinion best replaced before going offshore, especially singlehanded. 

The photo above shows the through mast reefing on a Husler 30 pictured in 1973, the mainsail had sliders, hence the pin just above opening in the slot to stop them falling out, OK until you needed more than a few turns when you had to pull the pin, most systems had bolt roped sails with lots more friction.

The “usual” problems are:

  • The sail often does not set well when reefed, particularly large and / or full cut sails.
  • Usually it can’t be operated with the boom more than about 40 degrees off the centre line and it really needs to be further in than that.
  • The Kicking strap / Vang attachment is problematic.
  • If the sail has a bolt rope there is a lot of friction, if the sail has sliders as in they have to be fed back into the mast slot as reefs are taken out.
The picture above shows round boom reefing from the inter war period on the 50 square metre "Sperling", once owned by, or allocated to, Herman Goering, kicking straps / vangs were not then in use, Uffa Fox claims to have invented them in the early 1950's. She is shown here in September 1974 heading into the Fal when she was operated by the RAF Sailing Association. She was one of the windfall boats “liberated” in 1945 and used by various regimental and service sailing associations into the 1970’s.

Kicking strap attachment for round boom reefing,
the claw is held in place with a rope to the end
of the boom or a bar coming back from the mast.

Stack Packs & Lazy Jacks

Sancerre at the start of the 2019 JBC
in > 20 knots of wind. The StackPack
 and Lazy Jacks are deployed with one
slab in the mainsail and everything is
nice and neat.
For anyone with a slab reefing system these are great and for the singlehanded sailor a real boon. 

The lazy jacks guide the sail down and the stack pack sides hold the bunt in place. When fully dropped you just zip it up and put a cover over the front section when you leave the boat. They work best with fully battened mainsails as there is a tendency, especially with big mainsails on fractionally rigged boats, for ordinary battens to snag during hoisting and when dropping they stack better. But don’t let that put you off using them with short battens, if push comes to shove and you want to hoist the main when off the wind drop the leeward side stays and off you go. 

Some makers are a bit mean with the Lazy Jack string, you need enough so that when using the full main (or hoisting off wind) you can drop them and secure them near the gooseneck thus avoiding black lines on and horrendous chaff damage to the sail. I have mine rigged so that undoing one clip each side will immediately change the length as required and a bit of shock cord tensions them so that they will stay put once hooked round the reefing horns, now only used in emergencies.

Slab Reefing Systems

Several modern takes on a system that has been used for hundreds of years.

Clew line positioning for slab reefing

The clew lines need to be positioned so that the cringle is held close to the boom and the foot kept in tension, how this is done will depend on the type and design of the sail and boom.

With External lines

This option will usually have to be taken if converting from roller reefing, with a wooden boom or if for some reason the boom does not have built in blocks or enough of them to handle the required number of lines. The downside is lots of rope hanging down from the boom – leading them through a couple of loops fixed to the boom will help. 

Sancerre’s slab reefing clew lines (above) using a Barton off the shelf system. Note the zipped exit holes in the stack pack to accommodate them, the picture was taken before I had a 3rd (storm) reef added to the sail.

The turning blocks, regrettably quite small but they do need to fit on the boom, are on sliders, the line goes through the block, up, through the leach cringle, back down and under the boom to be tied off on a loop provided on the slider. This means that both sides move together and can be positioned in the ideal spot for each reef. Unfortunately, a previous owner fitted the track about 4 inches too far aft for the front block to be perfectly positioned for the storm reef I added, but its close enough.

With Internal Lines

With internal lines and a mainsail with a full length bolt rope holding it to the boom this is a potential problem because the line coming out of the end of the boom will be at too shallow an angle to hold the clew close to the boom and whilst there may be somewhere on the boom to secure the free end it may not triangulate well. In a bad case, for instance on a storm reef, it may be necessary to lash the cringle to the boom with a separate line – but mind the battens and be careful not to lash in runners or other lines which could cause embarrassment as it did to at least one leading yacht on the 79 Fastnet, although they got away with it.

Positioning of clew lines will be somewhat easier with loose footed mainsails as the boom will be more accessible, some sailmakers offer a hybrid solution when a bolt rope is required by having the aft few feet of the foot loose with a slider aft so that the lines go under the sail and secured around the boom.

Mainsail modifications you may need to make

There are some modifications you may need to make for more comfortable sailing. Firstly, if yours has a bolt rope on the luff and the reefing system permits, it would probably be best to convert to sliders, they will make hoisting, reefing (even down-wind) and lowering much easier and on a cruising boat have negligible impact on performance. The mast will also have to be modified to stop the sliders falling out of the gate / feeder.

Make sure that sliders are closer together further up the mast, when reefed these will be under more strain in the high wind, if room permits the headboard should have two sliders on it to take the strain and to mitigate failure of one.

If going well offshore consideration should be given to adding a storm reef if a Trysail is not to be carried.

Slab reefing with horns

If replacing a round boom reefing system, this is the easiest to fit and the cheapest, especially on a small boat. Also as explained below it may be necessary to mix this system with one of the following to reduce the number of lines going aft.

Slab reefing horns (extreme right)

It doesn’t get much simpler than this, the sail is dropped until the cringle for the reef will go onto the horn and the halyard is tightened. This can be the tricky bit singlehanded if you have to go back to the cockpit to tighten the halyard as the cringle can fall off, but that can be worked round. To make it easier to attach the sail to the horn, rings can be put either side of the cringle and joined with webbing (sometimes referred to as “spectacles”), they will fit (and fall out!) much more easily.

The cleats shown were put on by a previous owner to take the clew lines, that just about works and saves taking lines back to the cockpit but it means a visit to the mast (as do the horns), and it is very difficult to get sufficient tension on them and the sail has to be fully depowered putting the reef in also it is not going to work when running. I have left the cleats there for emergencies. 

Booms designed with slab reefing in mind will usually have the lines running inside the boom, exiting below the gooseneck and may have jammers built in which works well on a crewed boat with the halyard and often pennant lines taken back to the cockpit and a man at the mast whilst reefing.

If converting to another slab system leave the horns on as well, you never know when they might be needed.

Single line slab reefing without “horns”

There are two main variants of this system, the simplest has a single line that runs from the cockpit to the mast, up and through the reefing cringle on the luff, down to the boom, out to the end of the boom, up to the leach reefing cringle then down to the boom. Ease the halyard, pull the reefing line in, then tighten the halyard. Job done.

Easy, except for all the friction and stretch in the system. The line will have gone through at least 4 blocks and 2 cringles and probably changed direction slightly through a clutch and some eyes keeping the lines in line below the goose neck. Even with additional blocks at the cringles, the friction can be horrendous, which will usually mean that the sail must be fully depowered. Shaking the reefs out can also be a difficult job

Reefing on a run, explained below, is usually not possible as the clew can’t be progressively tightened to ease the pressure on the sail from the shrouds.

If you are lucky enough to have a big boat, electric winches, amps to spare and have a fixed vang, all you need to do is ease the main, release one clutch, press two buttons in turn and then reset the clutch and mainsheet – very impressive. But apart from the friction which can make it hard work and slow to operate it is simple to use close hauled, reliable and there is only one, but very long, line to take to the cockpit.

The second version is more complicated and attempts to get the luff lightened before the clew, which seems like a good idea, unfortunately it introduces yet more friction by having a “shuttle block” inside the boom. Some internet searches under “Jiffy Reefing” found many diagrams for the first variant but very few for the second which I suspect reflects the current relative popularity of the two systems.

Dehler 41 "Blue Magic" coming into St Mawes,

Blue Magic has single line reefing and big electric winches to control a big mainsail. Note the blocks at the tack and clew reefing cringles to reduce friction and that the lead from the boom to the clew is well forward on the boom.

Two line slab reefing

In my view this is by far the best system, especially when shorthanded. Properly set up it is reliable, easy to use and quick, when on the wind or fetch I would expect to take 30 -  45 seconds to get my first reef in from the time I depower the main to having it powered up again, quicker than most fully crewed cruising boats I see in the Solent and up there with some of the racing boats. The trick is to have the lines in the right place, friction reduced as much as possible and a bit of practice.

The clew line is set up as for slab reefing with horns, then back to the cockpit and a second line run from aft up the side of the mast, through the luff reef cringle and down to below the boom where it is fixed slightly forward of the normal tack position. It may be necessary to have a block or more likely an eye at, or just below, the gooseneck to give a good lead but mine go directly from the blocks low down on the mast and they work well.

Starboard side clutches on Sancerre, left to right, kicker, 1st, 2nd
& 3rd reefing tack pennants then in prime position for the winch
the main halyard followed by a foredeck line and the topping lift.
On the port side the clew lines are 2nd, 3rd and 4th in from the hatch,
with the same colour codes and well positioned for the winch.

The secret to fast operation is not to be changing lines on a winch whilst you are reefing. Assuming that you need a winch for the clew lines and that you have two winches available this is easily managed because you should not need a winch on the tack line, if you do it is time to convert to sliders rather than using the bolt rope. 

So, the clew lines should be on the opposite side of the boat from the main halyard and the tack lines go where you can fit them in, ideally arranged as a mirror image of the clew lines and the same number of clutches from the centre so you can find them in the dark when you may not be able to make out the colour coding that you used.

Using a two line system reefing system

This is how to do it on any point of sailing except for a very broad reach or a run, no need to head up although, if sea state permits, heading up a little will make things easier when broad reaching:

  1. Rig the lazy jacks and release the stowed “StackPack” if necessary – I don’t need them for my first slab even though it is quite deep, but I do for the second and I often use it for the first as it is neater and it is then easier to put the second reef in or to drop the sail for storage. 
  2. Sort out the main halyard so it will run out easily – I flake if down. Have a winch handle ready to hand for that winch. 
  3. Take up the slack on the clew line and put a couple of turns around the winch, put the winch handle in if it locks in place, otherwise it is your choice. Take up the slack on the tack line.
  4. Unless you have a fixed vang that will support the boom, pull on the topping lift so that it will take the weight of the boom. On a masthead rig you may not need to ease off the kicker as the boom will probably be in the same position when done. The large mainsail on a fractionally rigged boat is more likely to need easing unless the flattening reef (Leach Cunningham) is already in. Leave the preventer alone if rigged.
  5. Depower the sail, on Sancerre when close hauled it will usually be enough just to let the traveller right down to leeward. 
  6. Release the main halyard clutch. If the sail has sliders the sail may come down quickly so try and stop the halyard from going too far!
  7. Pull on the tack line, as soon as the tack is in position set the clutch, grabbing the halyard to stop it running.
  8. Heave in, then winch in, the halyard until it is tight – a crease will normally form down the luff and using that as a guide experience will tell you when to stop. Set the clutch. If the winch is self-tailing it may be quicker to use it as an ordinary winch depending on how far you can typically pull the sail up without winching and the distance to go.
  9. Heave in on the clew line, initially you will only need to use the winch as a snubber, then use the handle if needed to get the clew into position. Set the clutch.
  10. Get the mainsail drawing.
  11. Ease the topping lift and tidy up.

Reefing down wind

This can be a problem in boats with swept back spreaders as there is just too much friction between the sail and the shrouds, but it should be no problem on boats with in-line spreaders and certainly works on the Achilles.

Proceed as above but with the following changes.

Don’t depower the sail at (5) if on a broad reach. On a run leave it right out except that with swept back spreaders it might help to pull in a bit to get the sail off them. Reset the preventer after any adjustment, the boom is best locked in position.

Pulling the tack line down will be much harder and may require the winch but go carefully. When it sticks, as it probably will, or gets harder to move, stop and pull in on the clew line to ease the pressure on the sail from the shrouds. Repeat as necessary until the tack is in position, then haul in on the clew to finish.

Mixing systems to reduce the number of lines

A fractionally rigged boat with a particularly large mainsail will certainly require 3 reefs, it may also have a flattening reef (a.k.a. a leach Cunningham which shortens the leach but not the luff to take fullness out of the sail) and if the boat does not have a trysail then a storm reef will also likely be required if going well offshore. 

With two line slab reefing with dedicated lines for all 4 reefs there would be 4 or 5 lines going to the clew and four going up the luff and probably a luff Cunningham as well, so potentially 10 lines to go back to the cockpit plus halyards, downhauls, toping lift, kicker and all the others. On most boats, especially smaller ones with less deck space that is just not a practical proposition, and clutches are expensive.

One option is to reuse some of the lines by reeving messengers between reef points so that with 2 set of lines when the second reef is put in and a third reef may be needed the line for the first reef is re-rove to be the 3rd reef and when the 3rd reef is put in the 2nd line can be used for the 4th reef.

On a sail with four reefs, the first reef tends to be used very frequently the 2nd reef quite often, the 3rd rarely and with luck the fourth reef never.

Another option is to use a combination of any of the slab reefing systems and perhaps some shared lines to reduce the number of lines, the problem is what combination? 

On a crewed boat sending someone to the mast to hook a reefing eye onto a horn whist someone else handles the halyard is not usually that big a deal, it’s been done for years, but singlehanded it becomes more problematic and which reef should be put to the horn? The first reef is used a lot so it will slow things down and create problems more often but at least the wind should not be too strong whereas doing that for the fourth reef means going forward by yourself in a tempest.

I’m afraid I don’t have an answer to that, there are so many combinations and boat specific issues (like how many other lines are needed, from where to where) it will have to be thought through on the boat and tried in practice. Once you have the maximum number of clutches that can be fitted, blocks etc. in place you can try all the alternates until you find the best one and, if appropriate, use different methods in different circumstances.

Sancerre at the start of the 2019 JBC, one
reef in and the stack pack in use as it would
be for the first 18 hours or so close hauled
in the F5-6 wind.
With a small high aspect mainsail only requiring two normal reefs and a storm reef I have enough clutches on the coach roof (7 aside, listed below) for almost everything I need, but I only reeve the storm slab clew line when it is likely to be required as is slows getting other reefs in and out and is a heavy line to have flopping about all the time. I don’t need it until the wind is well over 35 knots and in the channel, I would hope to be snug in some anchorage by then, recently most often Fowey 😊 or Portland. I have a messenger rigged on the leach and the reef line is through the clutch, spray hood and on to the end of the boom where it is secured. To keep the cockpit clear, the long bight is stored in a bag at the mast.

I can do similar with the tack line but usually reeve it as a luff Cunningham despite that rarely being required. Its only an 8mm line and I have room to store that in a halyard bag in the cockpit.

The picture above shows Sancerre with one slab in, the 2nd slab is just visible halfway between the 1st and the camber line. The new storm reef is a metre above that, at the bottom of the lower sail number. It reduces the sail to c 6 sq m.

In very severe weather I would probably risk a trip to the mast to back up the tack pennant for the storm reef with a sail tie or rope around the mast to reduce strain on the lower sliders.

Slab Reefing Tips

Use large diameter, oversized blocks where possible to help reduce friction.

It will be a bit harder on the hands but use a relatively thin line with a firm outer cover and a flexible inner, all will reduce friction. I use a Lyros "Herkules" a premium Polyester 8mm braid on braid line with blocks that will take 12mm line.

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