I’ve long been fascinated by the ancient square rig. It has been widely acclaimed for its downwind and reaching ability, but the traditional sails were often poor working upwind and required extensive rigging to do so. I wanted to experience what it was like to use the rig, and also to improve on its effectiveness using modern materials and aerodynamic theory. I built several square rigs for canoes and my peapod, and those results were rewarding.
One simple sail for my canoe was particularly instructive. I made it quickly, just a flat shower curtain with edge reinforcements and a fiberglass bicycle flagpole for a batten, slipped into a sleeve sewn in its foot. It would go downwind and broad-reach as well as the traditional rig’s reputation suggested. My friend Mike tried it out on his beautiful 1937 Peterborough canoe with only a paddle and boat trim for steering.
Downwind, these sails do best when they have some “belly” to contain the wind and minimize eddies curling around, destructively, to the front of the sail. We achieved this by pulling the battened foot of the sail up against the mast, then creating the belly by pulling the sheets further to the rear. We also found that we could pull one corner of the sail snug against the mast, and downward; when we did so the sail could be pulled fore-and-aft and would point higher.
Encouraged, I later built a bigger, carefully designed sail rig for my Gartside Riff catboat, ROSE. I used 4-oz Dacron sailcloth and gave it a lower spar to tension its foot, avoiding the complex rigging of historic ships. ROSE’s unstayed mast lets the sail rotate easily without being hindered by shrouds and stays. This sail is a rectangle slightly wider than it is tall. (Square rig sails came in many shapes and were only occasionally square; the name comes from the sail being hung perpendicular—square—to the mast.) I designed this sail as I would a contemporary balanced lug, with a loose foot, vertical panels, head and foot round, and broad-seamed to make the middle fuller than the top and bottom. The starboard edge is perfectly straight and built to withstand high tension while serving as a lugsail’s luff, while the port edge is hollowed a tiny bit to prevent it stretching and flapping when it’s serving as a lugsail’s leech. I also moved the deepest draft from center to 5 percent toward the starboard edge to give better control in fore-and-aft mode. The loose foot can be tightened for upwind work and loosened for downwind, creating the desired belly. When loosened, the effective center of effort moves back toward the middle of the sail.
The sail operates in two distinctive modes: across and down wind, with the yard square to the mast, and upwind, with the sail hauled fore-and aft. Going downwind in the square mode, the sail is docile and easy to handle. In the upwind mode, the rig can also work across and downwind, but downwind steering is, as you’d expect of a sail set well outboard to one side of the hull, much more demanding of the skipper.
A 4:1 downhaul is attached to the center of the lower spar for the square-sail mode, or near the starboard/front edge for lug-sail mode. Either way, this allows the edges to be tensioned, which is essential as it lets the sail develop aerodynamic lift and point higher. The leading-edge tension in fore-and-aft mode is much higher, creating the taut luff that is the key to best upwind performance.
In square mode I can run and beam-reach through a downwind arc of 190 degrees and more. When I take a couple of minutes to change mode to fore-and-aft, I move the downhaul point and change the sheets. The sail is now rigged like a balanced lug, and in this mode I can tack reliably and point as close as 55 compass degrees to the wind. Not too bad for a lugsail, let alone a square sail! With almost 30 percent of the sail forward of the mast in lug mode, one must tack rather decisively to keep from being backwinded, and this takes a bit of practice.
I am quite satisfied with my new sail. It performs better upwind than I expected, given its low aspect ratio. The current rigging gets the job done, but there remains room for new thinking on the arrangements: I’d like to make the transition between modes quicker and easier to do without going forward.
My experiments with square rigs have satisfied my curiosity and exceeded my expectations. I think this sort of contemporary square rig has good potential for sailing courses that include lots of downwind work, for which square format is quite docile. When higher reaching and upwind work is called for, it can be changed to the lug mode. Lugsails appear to be the heirs apparent to the square rig, and this two-mode setup gave me a glimpse at the how and why.
Bob Cavenagh grew up in a navy family and lived in seaports and around ships and boats from infancy. At the age of five he built his first boat; it sank immediately. After college, Army, and grad school he began an academic career, bought his first sailboat and canoe in 1975, and has been an enthusiastic sailor ever since. For the last three decades he has pursued a particular interest in rigs and sailmaking. Now retired, he spends summers sailing a small fleet of small boats on a Canadian lake.
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