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Old 07-12-2002
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Boom Furling Revolution

This article was originally published August 2001 on SailNet.


Gone are the clunky, circa-'50s boom-furling systems, replaced these days by more functional furlers that allow sails to retain much of their optimum shape while partially furled.

Sailors often travel in full circles, and such has been the case with boom reefing and furling. In the 1940s and '50s, Eric Hiscock and others touted the advantages of mechanical roller reefing. These early units often consisted of a crank driving a worm gear assembly that rotated the boom. While they worked, the original boom roller-reefing gears left much to be desired.

The first obstacle was that fittings could only be attached at the boom ends, eliminating the use of boom vangs, mid-point mainsheets, and other desirable hardware. If you've been sailing long enough, you may remember special "boom claws," metal rings with rollers, that could ride on the reefed sailcloth with only minimal damage.

There were other problems with the old roller-reefing systems. The sail had to be battenless, or have the battens installed parallel to the foot of the sail, which reduced sail area. Sail track gates usually had to be custom-built to let the slides off the track as the sail was rolled down. The boom had to be round, which is not a good shape for strength, and these booms usually ended up far heavier than would have been necessary otherwise—a curse in light airs.

By far, the worst problem with the old roller reefing, however, was "boom droop." The sailcloth at the gooseneck, heavily reinforced at the tack and containing a boltrope, would build up a considerable bulk as it was rolled down. The leech, on the other hand, spiraled forward along the boom and developed very little girth. After a few turns, the difference in diameter allowed the outboard end of the boom to drop dangerously close to the helmsman's head. Tapered booms were tried, and they always looked odd being small at the gooseneck and fat near the mainsheet. The best ad hoc solution I ever saw was a boat whose captain stuffed the cockpit cushions into the leech as the sail was reefed.


Modern in-boom furlers now have smaller yet well-functioning parts.

Still, the desire for a furling mainsails grew. The next generation furled the mainsail on the vertical axis into the mast as this was the easiest to perfect, but this methodology also has limitations. Whether behind-the-mast, in-mast, or internal add-on,roller furling systems put a great deal of windage and weight high up in the air where it is least desirable. Repairs on many of these systems involve extensive disassembly, often well above the deck. Even a perfectly cut sail in a housed unit usually has less than an optimal performance shape when reefed. The sail must be loose-footed and cut high at the clew, further reducing sail area. And battens are next to impossible, thus eliminating the ability to add sail area or improve shape.

While all this work with vertical furling was going on, however, other designers were still attempting to turn boom-based roller-reefing into a workable approach to furling. In the mid 1980s, the ever-daring Hood company introduced a boom furling system they called the Sto-Boom. Still in production in both Europe and the US, the Sto-Boom was not initially a commercial success, especially with larger boats. A second boom furler manufactured in Denmark under the name of SailTainer no longer has a US distributor.

The lack of development during this period was due to several major obstacles inherent in boom-furler design. First, the space required to insert the furling drum and necessary universal joints between the mast and the boom forces the luff of the mainsail far aft, thus creating a need for innovative sail track design. A second problem is that the boom must be at the same horizontal angle to the mast each time reefing is attempted in order to avoid bunching the sail up or jamming the whole system. A third factor is simply the weight of the mainsail and friction on the sail track. Hoisting is still required when furling a mainsail on a horizontal axis, and big boats often find that electric or hydraulic winches are needed for the halyard.


Modern roller furling booms stand ready to tackle even the largest sails—including those in found on mega-yachts.
Decades of tinkering are beginning to pay off. In the past few years, Leisure Furl, Profurl, and Furlboom have created three new in-boom mainsail furling products that are garnering a great deal of praise. All three claim to be adaptable to existing masts on boats up to approximately 60 feet, and to have solved the engineering difficulties around the gooseneck and sail track. All claim to accept mainsails with long battens—a great leap forward in furling mainsail performance, and all have achieved these feats in unique ways.

Rolling Your Way Home

If you're sold on boom-based roller-furling and you're setting out to change over to one of these systems, keep in mind that this will indeed be a major project. All three of the most popular brands (Leisure Furl, Profurl, and Furlboom) are imported into the US and may involve shipping delays. Installation time and a shakedown period are required, so don't wait until two weeks before the big cruise to order one. Here are a few additional tips for converting to a roller-furling boom.

  • While a few sailors would be able to install these systems themselves, most of us would choose a simpler task like re-powering or changing keels. It isn't simple. Use an installer who has successfully completed several of the brand you are purchasing—don't let an inexperienced rigger experiment on your time.
  • Buy a new mainsail with the system and make sure the sailmaker works with the rigger. Converting an old mainsail may save a few dollars initially, but will give disappointing results. Mainsails for roller furling booms require very careful planning of the boltrope area and reinforcement patches. The required shapes are also new to most sailmakers unfamiliar with these systems.
  • Install a solid rod vang. The angle between mast and boom continues to be critical with in-boom furlers, and most problems are traced to not maintaining this angle. Sailcloth bunches along the foils, luffs jam in the sail track, and fervent oaths are heard across the water when this angle varies by more than a degree or two. The vang needs to be beefy enough to take the unrelieved strain of maintaining a constant angle between mast and boom.



Suggested Reading:

Roller Furler Layup by Tom Wood

Leading Sail Controls Aft by Sue and Larry

Installing Roller Furling by Sue and Larry

SailNet Store Section: Mainsail Reefing and Furling Systems

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