Main Sail Furling & Reefing Systems

Main Sail Furling & Reefing Systems

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Caliber 40 "Windom",

Above Image Caliber 40 "Windom", with in mast Furler

This article compares the various methods of reefing the main sail, specifically mainsail reefing systems. We look at each type of main reefing systems, describe the mainsail reefing equipment, describe reefing techniques, and mainsail reefing tips. We then look at the Pros and Cons of each system.

At the Annapolis sail Boat Show 2008 one of our readers asked an easy question. Which is the best mainsail reefing/furling system? Easy question but not a simple answer.

We decided to look at all the sailboats specifically keel Boats, at the 2008 Annapolis Boat show and do a survey of which system is the most popular.

Mainsail reefing & furling Survey

The Annapolis sailboat show has many racers and cruisers on show. We took the opportunity to see how each type, cruiser or racer, tackles mainsail reefing.

There are 3 types of main sail reefing;

  • Slab reefing
  • In mast furling systems
  • Boom furling systems.

The survey is based on all boats over 28ft. The boats using In mast furlers are the larger production builders, Catalina, Hunter, Beneteau, Island packet etc.


Survey Annapolis Boat Show 2008


Reefing type

# boats


In Mast Furlers



Boom Furlers



Slab reefing bolt rope



Slab reefing sides and Lazy Jacks



Slab reefing sides and Dutchman system


In mast furling is the most popular method of main sail handling as its found on most of the major production Boats, but if you add up all the slab reefing options you have 76 ie the most.

Note; As of 2010 two years after the 2008 show, there has not been any major change so we continue to see results similar to the 2008 survey.

Mainsail Reefing

Leisure furl

Leisure furl

In mast furling is the most popular method of main sail handling as its found on most of the major production Boats.

Roller furling Booms are typically found on high end and larger boats and most used the Leisure Furl from Forespar. Boats in this category are the Trintella, Morris, Hylas, Friendship etc. Hylas had the GMT boom.

Slab reefing systems incorporated 3 types. Bolt rope and slides, lazy jacks and Dutchman systems. The performance cruisers use systems to capture the mainsail when it drops, like the Dutchman and lazy Jacks systems. I was surprised to see so many lazy Jacks as IMHO the Dutchman system is the better system, as it flakes the sail as its drops, but it is also more expensive.

The performance orientated boats including the racers tend to go with slides or bolt rope and slab reefing.

Mainsail Slab reefing

Slab reefing is the most traditional & simplest form of reefing. You only need some grommets in the sail and some blocks and reefing lines to make this system work.

A list of production yachts at the Annapolis Boat Show using Slab reefing include;
Impression, Dufour , Southerly, Outbound, Fingulf, Valiant, Delphia, Grand Solie, X41, Wauquiez, J Boats, Shannon, Catamarans, marla, Geronimo, Fountain Pajot, Alerion, Etap, Sabre, Hanse, Tartan, Caliber, Sunsail, Moorings, Hunter, Morris, Crealock,

How slab reefing works

Harken page slab reefing layout and equipment

Harken slab reefing

Harken slab reefing

The slab reefing system is the cheapest simplest and easiest to add to your main. This Harken diagram details the blocks and lines you need to assemble a slab reefing system

Video tips on slab reefing

Single Line reefing makes slab reefing simple. Instead of a reef line for the tack and the clew, there is one line for both. The process of reefing involves easing the main halyard to the desired point and then taking up on the single reef line. The line starts by pulling the tack of the main down tightening the luff and then the load automatically pulls the leech tight.

Slab Reefing






Physical effort



May involve getting out of cockpit



High reach for boom cover


Easy modification

Loose sail material after reef


Mainsail Slab reefing

Dutchman system

Dutchman system

Dutchman system

When you use a slab reefing system you will find as the sail is lowered it flaps around a lot. There is nothing to hold it in place. This may not be a problem and once you have secured the reef, there are grommets in the sail to tie the loose sail down.

However there are two systems you can add to control the sail; the Dutchamn System and the Lazy Jack System.

The Dutchman system helps the mainsail fold itself while lowering. The Dutchman lines are led from side to side through the sail. Its almost automatic flaking.

Imagine a window blind that has a central line that goes through each slat. this is how to look at the Dutchman System. While reefing the Dutchman works the same way flaking the sail until you get to the reef point.

To use a Dutchman System you will need sail slides on your mainsail. It will not work on a bolt rope mainsail.

To learn more about the Dutchman System click here

Mainsail Slab reefing

Lazy Jacks

harken lazy jacks

Along with the Dutchman System, lazy jacks are another way of capturing the mainsail while its drops or is reefed.

Lazy Jacks work by having lines either side of the mainsail. Hence the main sail is always captured between the lines so when you lower the sail it so captured and will no fall on the deck.

This diagram from Harken shows how the system works

This link will take you to more information on Lazy jacks

Mainsail Slab reefing

Main sail slide system and Boom w Lazy Jacks

Gull Wing Boom

Shipman 65

Hall Boom

There is a mainsail on that boom even though you would think it was a bare boom until you see the head at the front end. It is not a furling boom, the main sail is simply flaked, with the help of lazy jacks. Typically you would see a lot of sail sitting on top of the boom plus a stack of battcars at the luff.

The combination of Halls gull wing composite boom and Harkens Switch T track which reduces the height of the mainsail cars, makes for a very clean look on the Shipman 65.

Mainsail Slab reefing

Harken Switch Track

lower stack height of batten cars

Shipman 65

Harken Swith Track mainsail batten car track

The Switch T Track looks like a railway switching system. The battcars alternatly fall down the portside then the starboard side helping the sail flake itself and lower stack height.

In the picture of the forward end of the boom you can see the Switch T Track just above the mainsail cover. You can see lazy jacks pulled forward in the picture above. Lazy jacks work well with Antals low friction rings

Other mainsail Luff batten car systems

A car system that will help the mainsail raising and lowering is Ronstans balls slide cars this car has ball bearings yet will fit in a bolt rope track.

Yet another is Tides Strong track

In Mast Furling

The basic design is a roller furler unit fitted inside a mast section that has a slot in the aft end that the mainsail rolls in and out of. This mast section is larger than normally required and may require less spreaders due to the extra stiffness. The mainsail because it furls like a jib cannot support battens, hence the mainsail needs to be cut with leach hollow like a jib/genoa.

In Mast Furling

mast furler

mast furler

A list of production yachts at the Annapolis Boat Show using In mast furling include;
Jeaneau, Hunter, caliber, Gozzard, Fingulf, Oyster, Hylas, Halberg Rassey, Bavaria, Island Packet, Catalina 6, Dufour, Beneteau, cruisers, Passport, Robi, Impression, & Wauquiez,

The Sparcraft in mast furler is one example of in mast furlers

Points to consider & potential problems;

In mast furling although a very convenient furling system it does has its pitfalls. The Z Spars link to in mast furling help describes some of the pitfalls and how to overcome them.

In Mast Furling



Weight up high

Simple to use

Reduced sail area

No boom cover

Poor light air performance

Furl to any sail size

If the main furler jams you may not unable to drop main

In Mast Furling

Increasing sail Area

One complaint about mast furlers is the reduced sail area from the leech hollow. there are a couple of ways of increasing sail area.

The air batten From Halsey is an inflatable batten which is inflated when the sail is set, giving you much more sail area. More

Another idea from Halsey is the vertical batten.

In Mast Furling

Modifying an existing mast



There are some behind the mast options that you can retrofit your existing mast if you wish to convert to main sail reefing. Bamar external mast furling unit to add to existing mast section.

Boom Furling

The Boom Furling system works similarly to slab reefing. The main halyard is dropped and the lower part of the main sail is rolled up into a mandrill located inside the boom.

One critical feature of boom furlers is the angle of the boom to mast. This is specified by the manufacturer and you will need some sort of solid vang to control this angle.

A list of production yachts at the Annapolis Boat Show using Boom furling include;
Hylas 70ft, Trintella, Niad, Cabo Rico, Westsail 42, Saga, and Tartan 4400.

There are several Boom furlers including Schaefer BoomFurl, GMT PowerFurl and FurlBoom and Forespar/Leisure furl among others.

Boom Furling

Schaefer BoomFurl

Schaefer BoomFurl

Schaefer BoomFurl

Two points of interest in the Boom Furl are the aft track on the mast and the aft furling drum which make retro fitting possible with out huge modifications.

The unique Sail Track and feeder combine to precisely transfer any fully battened main to the mandrel located within the boom. The Sail Track is mounted to the back of the mast to allow the entire system to articulate on the same axis, for easy hoisting, reefing and stowing at any apparent wind angle.

The front end of the Schafer BoomFurl is machined out of a large alloy block. This allows for easy inspection of the Luff tape and furling operation

Placing the furler drum at the aft end of the boom eliminates the need to drill large holes through the mast to mount the drum forward of the mast where it can foul lines.

Boom Furling

Forespars Coastal system

Coastal system

Coastal system

Forespars Coastal system is the smaller boat version of the Leisure furl and is shown on the Catalina 30 pictured below. The coastal system has the furling drum in the boom at the aft end and so does not go through the mast, unlike the traditional Leisure furl.

Video Mainsail Furling Demonstration from Forespar.

Used Forespar Coastal system

Boom Furling Pros


Large sail area power

Boom furling most expensive

Full battens

Most complex

Reef to any sail size

Boom angle critical

No boom cover needed


Low C of G


If it jams you can slab reef


Other Mainsail Flaking systems

Doyle Stackpack



Stackpacks were invented by Doyle sails as a way to enclose the mainsail after flaking in an easy manner. The mainsail cover is basically part of the system so you do not need to store and retrieve the cover every time you go sailing. The lazy jacks capture the sail as its drops and then all you need to do is zip up the top of the cover.

Introduced in 1983, DOYLE StackPack is the original trouble free mainsail furling system for the cruising sailor The simplest, easiest way to handle your mainsail Proven to be the most innovative and cost-effective mainsail handling system ever Maintains mainsail speed & shape - lies flat against the sail while sailing Available as a retrofit for your existing sail

StackPack is a fully battened mainsail with integral lazy jacks and a cover that opens automatically to accept the sail as it is lowered. The cover and lazy jack system neatly flakes and holds the sail as it is lowered or reefed. The folds at the foot of a reefed mainsail also lie neatly in the StackPack cover, eliminating the need to tie off the excess fabric with ties. With the sail completely stowed, the StackPack system presents a neat appearance and automatically protects the sail from harmful UV rays. While sailing, the integral cover lies flat against the foot of the sail for a clean aerodynamic effect.

More Sailmakers these days are producing their version of the stackpack, so ask your sailmaker.


The most obvious observation after starting my survey was realizing how popular in the mast mainsail furling is. They numbered almost as many as the slab reefing systems. The main reason for this is the number of production cruiser manufacturers that choose to install in the mast furling as standard.

Boom furling although having the best pros is an expensive and intricate system. Many large yachts employ Boom furling as the cost is a smaller percentage of the overall cost of the boat, however there are smaller boats using boom furling systems for the ease of use.

There is not a reefing system that is perfect. Each has its own compromises, so look at the pros and cons for each system before choosing the one for you.

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