Main Sail Furling Systems – Standard, In-mast, In-boom

Roller Reefing Spruce Boom

The way you stow your sails is an old problem dating back to the beginning of sailing. As far back as you research, sailors have experimented with various ways to facilitate head and main sail control. Lazy jacks are a good example of an ancient idea used for many centuries named after British maritime nickname of “jacks.” Whatever their orientation, lazy jacks essentially are two webs of lines on either side of the main which corral when de-powering and ease mainsail flaking. Another example is slab reefing where you tie down the mainsail at tack and clew reef cringles with a reef line run through the clew reef cringle and possibly another tack reef line. Before modern rigs, mariners experimented with all types of reefing, flaking, and even furling systems.

Starting the early 1990’s, English craftsmen invented and produced the Wykeham-Martin Furling gear, the first headsail furling system. The gear rotated via top and bottom swivels attached directly to the head and tack of the jib. Torque transmitted from the lower to upper swivel via a wire thread along the luff of the headsail. This arrangement in contrast to modern units prevented sailors from obtaining a defined sail shape when the they partially furled, i.e. reefed, the headsail. With the Wykeham gear either you flew all the sail or none. The company is still making these beautiful and traditional units and boasts of being in continuous production 100 years.

Reefing on a standard rig is accomplished by a slab reefing system. It is essentially a manual way to furl up the mainsail. Slab, aka jiffy, reefing is best described by the following sequence of commands:

  1. Loosen the main halyard
  2. Take in the tack reef line to the appropriate reef point
  3. Take in the clew reef line to the same reef point
  4. Tighten the main halyard

There are variations on this simple theme of securing the main sail at two points. Some systems do not have a tack reef line and instead rely on a tack hook. Such a slab reefing system with only a clew line is a “one line” system. Some systems have nettles which when secured perfectly flake the reef across the foot. Nettles are cringles with lines thread through at the same level between the clew and tack points.

The current era of mainsail furling systems to manage sailplans traces its roots back to the first half of the 20th century when some wooden boat manufacturers experimented with primitive boom furlers. These booms rotated at the gooseneck wrapping the mainsail around the boom. While a novel idea, the implementation was not acceptable. The process was finicky and when partially rolled tended to slide along the boom leading to poor sail shape. These relics of the early to mid 1990’s attest to marine ingenuity. It would be many years until we would think to revisit and perfect this idea.

The era of modern headsail furling kicked of with the introduction in USA of the headsail furling system in the 1960’s by Murray Scheiner in New York. Previously all staysails were hanked on, taken down, and stowed in a locker. Murray was inspired by a fellow disabled sailor who could not handle this process. The idea spread and the first widely adopted unit was designed by Tim Stearn. Manufacturers would begin rapidly improving and launching new products every seven to fifteen years – about the time it takes for service teams to see what engineering ideas work the best by evaluating real world feedback.

Introduced in 1973, the popular Twinstay was the successor to Stearn’s original Hyde System design. The Twinstay became especially popular in racing cycles. Yachts could hoist a new headsail before taking down the old one and avoid the performance loss of a bald headed sail change. During the late 1970’s, headsail roller furling systems were perfected and led to a large industry populated by Hood’s Seafurl, Profurl’s ProEnsign, and Seldon’s Furlex models to name a few. Hood’s Seafurl unit became the dominant standard on production yachts such as Oday. Hood Yacht Systems would become the leading innovator in mainsail furling systems.

Wykeham Martin Furling Gear

Hood Systems in the late 1970’s introduced the first commercial in-mast furling system – the Hood Stowaway. This legendary piece of equipment is still featured on many vintage yachts of this era such as Bristols and Gulfstars. In contrast to a standard spar with in-mast furling, storage is completely inside the mast with no mainsail cover necessary. The sail rolls up on a spool protected inside the mast casing leaving the mainsail always ready, tucked neatly out of view inside the mast.

This innovation of in-mast furling has proved a double edged letter opener. While storing, hoisting, and reefing the mainsail is much easier, the vertical rolling necessitates the use of batten-less sails and the mechanism inside the mast necessitates a larger diameter spar and more weight aloft. In-mast furling causes significant trade-offs in performance with estimates of 20% less sail area on the roachless sails. You pay for it too. Switching from a standard spar to in-mast furling will run $30,000 dollars for installation and the new spar.

Even with the limitations, in-mast furling makes a good deal of sense on sloop rigged, center cockpit yachts over 45-feet in length where the mainsail is onerous to handle. Hoisting and reefing the mainsail can be as much as flicking a switch. And as you find out, most cruising is done under a reefed main anyways, so the sail area trade-off is much less significant than the numbers suggest. With furling, a single-hander can hoist and reef the mainsail without ever leaving the cockpit which is rarely the case on standard rigs with slab reefing and lazy jacks even when all lines thread through to the cockpit. Sailing an in-mast furled main is much safer offshore as long as the system functions properly.

In-mast furling stows the mainsail inside the mast.
In-mast furling stows the mainsail inside the mast.

In 1983, Doyle Sailmakers introduced the Stack-Pack which along with lazy jacks makes flaking a standard main as easy as yet. A stack pack is a mainsail canvas cover which secures to the boom and is held open at the top by lazy jacks. Thereby the main sail naturally falls into her canvas cover. A zipper at the top finishes the arrangement to protect the mainsail from UV light. If you do not have furling, a Stack-Pack is an excellent way to stow the mainsail.

In 1986, Martinus van Breens started publicizing his invention called the Dutchman system. In this mainsail flaking system, meant as an alternative to lazy jacks, filaments thread through cringles in the mainsail and secure into the topping lift. This installation of vertical filaments creates a track over which the main sail flakes better than with lazy jacks. In trade, sails have to have cringles (holes) cut in them to thread through the filaments. While not necessarily ruined, such sails are forever Dutchman system sails.

Dutchman System

In the late 1980’s came through another innovation from Hood Systems, the Hood Sto-boom, spurred on by the popularity of in-mast furling despite their limitations. Like the primitive rotating booms of yester years, this system sought to use the boom as a reefing and stowing platform. Inside the mast was installed a spool over which the mainsail could furl onto and hide inside. Electric motors automated the mechanism for easy handling from the cockpit.

At first sweet waft, in-boom furling seems to have all the benefits and none of the performance drawbacks of in-mast furling. A horizontally furling main still can have full battens and use a traditional mast. The boom is accessible via the deck if any problems occur. It is easy to reach up and unclog the boom unlike scurrying aloft. And if all fails, with in-boom furling you can go back to standard and just tie up the sail on top of the boom and use a sail cover. In-boom furling falls back to the standard rig.

But sailors soon found that the Hood Sto-boom while novel was a terrible engineering mistake. It was costly, complicated, and less convenient than standard spars. The mechanism easily jammed and required perfect boom angle alignment and wind conditions to furl correctly and not chafe the luff. The failures of the Hood Sto-boom gave in-boom furling a bad reputation which it is still overcoming.

During the early 1990’s, Forespar from New Zealand introduced a greatly improved in-boom furling system called LeisureFurl which is still the dominant product today. Other manufacturers followed dress such as Denmark’s John Mast, France’s Profurl, and Australia’s Furlboom in the late 1990’s. Most recently in the mid 2000’s Schaefer introduced an exceptional in-boom furling system that allows for reefing off wind. For new Hylas yachts and other manufacturers, the Schaffer in-boom furling system has become a popular option and rightly so as it rarely catches.

Even today with all the improvements, standard, in-mast, and in-boom furling all have a place in a sailor’s consideration. As with every yacht topic, it depends on the scenario – how the boat is going to be sailed, where, and by whom. And of course, price is a factor. Prices are higher for in-mast and in-boom furling units. To convert a 45′ yacht with standard rigging to in-mast furling is around $30,000. A standard rigged mast costs around $18,000. Expect to pay a premium of $15,000 for an in-mast or in-boom furled yacht. Who knows what we will see next with the wing sails of America’s Cup spreading to cruising design. Or maybe manufacturers have reached parity with the efficient systems that equip current yachts.

3 Replies to “Main Sail Furling Systems – Standard, In-mast, In-boom”

  1. Ahoy, me name is Fox Axel the Pirate. Some thinks these newfangled furlings are fer sissies. Maybe, Big Red likes sackcloth and ashes, but the Pirate of Monkey Isle likes to be pampered. Me bought me in-mast furler off a landlubber’s rig. With all me treasure and booty, me canst have whatever me wants. Though it ergs me, me ship is a fine yacht tricked out in all me pirate ways. Be fair about these rigs, all have their sharp points. Avast, me must bludgeon a swab. Pieces of eight!

  2. Arghh, I’m back. the times a changing. I used to have nigh a prop on my clipper. These days dis ere scoundrel keeps a high-tech pirate ship with all the latest gear. It ain’t no shame and the wenches just can’t keep away from me. Aye, furling systems are one of the best options. A light breeze, cocktails, and naught to tend with me in-mast furler. Just a fine cruise off Monkey Isle with me lady. Keep your minds open me mateys – Black Fox the Pirate.

  3. Not bad article, but I really miss that you didn’t express your opinion, but ok you just have different approach

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