This article was originally published August 2001 on SailNet.
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.
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.
Roller Furler Layup by Tom Wood
Leading Sail Controls Aft by Sue and Larry
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