Traditionally, all sailboat mainsails were reefed by simply pulling down the reefing lines through cringles in the luff and leech of the mainsail, then securing the reefing pennants—often permanently attached to the mainsail—to the boom to tidy the sail up.
Then, in the late 1960s, the rolling boom was developed. This was thought to be easier than simple slab reefing and allowed the skipper to reef down through an infinite number of sail sizes, rather than the fixed slab dictated by the sail cringles.
Though some liked it, roller boom furling never became very popular as it required the vang to be removed before rolling, after which one crewmember would turn a furling handle at the mast while a second released the halyard and a third pulled back on the leech of the sail to prevent it from creasing and bunching up.
To prevent the sail from becoming hopelessly baggy when rolled, it also had to either have been designed with a reduced belly or you’d have to place lengths of foam or rolled towels inside the roll toward the center of the sail, which worked rather like the foam you find on the luff of a furling headsail today.
Finally, the vang could only be reattached using a horseshoe style attachment that wrapped around both the boom and the sail, and often chafed the latter. For all these reasons, roller boom furling was eventually all but abandoned.
Boom furling systems have since re-emerged, mainly on boats above 50ft LOA. However, rather than having the sail roll around the boom, the new designs feature a lightweight composite “shell,” or “trough,” in the middle of which runs atapered mandrel (spindle) around which the sail rolls. The shape of the mandrel—thicker in the middle, and tapering down toward the ends—solves the problem of taking up the belly of the sail, and the shell allows a vang to be permanently mounted. In fact, a permanent vang is essential, as the boom must be kept at the correct angle to the mast when furling.
Most boom furlers are electrically driven, although some smaller versions are available with a manual drive at the mast. Some systems have a furling drum, rather like those on a furling headsail, on the leading edge of the mast, from which a furling line can be led aft to a manual or electric winch in the cockpit for simplified reefing.
Unlike in-mast furling systems, with a boom furler the mainsail can still be lowered if the mechanism fails or jams. Boom furlers also allow sailmakers to incorporate regular horizontal battens in the main.
MODERN BOOM FURLER
Pros
• Sail area can be reduced incrementally
• Can still use horizontal battens
• Neat way of storing the reefed sail
• Can be operated from the cockpit
• Sail can still be lowered normally if system fails
Cons
• Extra complexity
• Boom needs to be at correct angle or sail will not roll properly
Slab Reefing
In the early 1970s, mainstream rig builders modified the traditional slab reef method so that a reef could be put in by a single crewmember, fitting a ram’s horn for the luff cringles and reeving the leech reefing lines through blocks at the after end of the boom and then leading them forward (usually inside the boom) through jammers to winches or cleats on the mast.
A good number of roller furling booms were subsequently modified to slab reefing by fitting a ram’s horn for the luff cringles and attaching cheek blocks to the after end of the boom. You can do this by riveting eyes in the correct position at the sides of the boom, to which blocks are then attached. If you can remove the end cap from the boom and through-bolt these eyes with aluminium backing plates, even better. The leech lines are then led through the blocks and jammers, to a reefing winch on the mast, the same as with any other slab-reefing arrangement.
Whichever method you choose, it is important that one side of the leech reefing line (usually the end that’s tied down to the boom) be attached in such a way as to exert a certain amount of backward, as well as downward, pull on the leech of the sail, in order to retain tension along the foot. In heavier air you want the main to be as flat as possible to minimize the heeling forces at work and make it easier to keep your boat under control.
Although traditional slab reefing requires that a crewmember go up to the mast to put the luff cringle over the horn, many sailors prefer this method for its simplicity and because it requires a minimal amount of line. For increased security, those who reef at the mast often fit stout granny bars on which they can lean in heavy weather.
You can take the basic slab-reefing approach one step further by running lines through the luff cringles too, so that instead of needing to hook them over a horn, both luff and leech reefing lines can be led down to the foot of the mast and back to rope clutches and a halyard winch on the coachroof (Figure 1). Such a two-line system allows one person to put a reef in from the cockpit, provided the main halyard is also led aft.
SLAB REEFING
Pros
• Can be done singlehandedly and relatively quickly
• Minimal reefing line required
• Lower friction than single-line reefing
Cons
• Requires additional blocks, jammers and mast winches
• Requires a crewmember to go to the mast
TWO-LINE REEFING
Pros
• Allows single-handed reefing from the security of the cockpit
Cons
• Requires turning blocks at the mast base and rope clutches at the halyard winch
• Results in lots of cockpit spaghetti
Single-line reefing
Single-line reefing, in which a single line runs to both the tack and the clew, simplifies the reefing process and is the most popular method of slab reefing today. Its drawbacks include the increased friction induced in the system through the inclusion of yet more turning blocks. Pulling a single reefing line initially hauls down the luff until the reefing cringle is pulled down to the gooseneck. After that, the load is automatically transferred to the block at the clew where it begins pulling down the leech—much as you would start by pulling down the luff line, followed by the leech line, in a two-line system.
There are two common methods of single-line reefing. The first, which can be retrofitted to a standard slab reef boom, incorporates a single, continuous line that leads through a block where the luff cringle would normally be, back down to a turning block on the outside of the boom, along the boom to a second turning block, and back up to a second block/cringle in the leech, before terminating at the boom end.
To upgrade a simple slab reef system, you should replace the regular reefing cringles with turning blocks of some sort to keep the friction to a minimum. Leaving the leech cringles as standard, simply reeving the line through the ring and down to the boom, adds to the already excessive friction in the system. By lashing together two stainless steel rings with a diameter larger than the cringle ring itself, one either side of the sail, you can provide a strong fixing point for a block. Blocks should ideally have smooth, plasticized covers to avoid chafing on the sail unless they are the type that can actually be sewn onto the sail itself.
The second method, used by some sparmakers, actually uses two separate lines, but only one activates the reef. This involves placing a free-moving plate with a block at each end within the boom itself. The reefing line is then led from the cockpit to the mast foot, up to the boom, around the forward block on the plate, back to a turning block forward, then up to a cringle or block and down again to terminate to a fixed anchor point on the mast or boom. A second line is then run from an anchor point inside the boom, around the aft plate block, back to a turning block in the end of the boom, up to the reef cringle/block on the sail leech and finally back down to the boom.
As you can see in Figure B, pulling on the reefing line at the cockpit end first pulls the luff down (line of least resistance) until it reaches the boom. Then, when it can go no farther, the internal block plate starts to move forward, pulling down the leech pennant until it too reaches the boom. The downside to this system is there’s a great deal of friction, and if one of the lines breaks (which has happened to me during an ocean crossing), you can end up with a mass of spaghetti jammed inside the boom!
In most cases, single-line reefing is only provided for the first two reefs. If you have a third, it will have to be treated as a standard slab reef and tied down manually. The one time you wouldn’t want to be on deck grappling with a manual reef is when conditions are bad enough to need a third reef! Perhaps bluewater sailors should consider fitting the cockpit-controlled, single-line reefing system to reefs 2 and 3 and keep the first reef as manual. It would make more sense, although it would require considerably longer reefing lines.
Needless to say, the blocks in either of these systems need to be the low-friction, ball bearing type. It is also wise to pair these systems with lazyjacks and a sail bag to tidy up the reefed sail and keep it from falling onto the deck and restricting the helm’s view forward. If you prefer, you can still incorporate reefing pennants or cringles into the sail and tie the reefed sail up neatly, but that means leaving the cockpit, which defeats the primary object of single-line reefing.
Photos by Peter Nielsen; diagrams by Alastair Garrod
