Why Slider has a Sprit-sloop Rig

The first thing most sailors notice about Slider is her sprit mainsail.

Boats with traditional, low-tech rigs are uncommon in most sailing areas, and it’s no different here in the Florida panhandle. We have a couple of gaff schooners over in Destin, and there may be other character boats around, but they rarely make an appearance on the bay.

When these sailors notice that Slider is a catamaran, their degree of surprise ramps up a few notches. Multihulls seem to be regarded as innately high-tech machines. Maybe folks have forgotten that the ancestors of these craft carried people swiftly to every corner of the Pacific, using only wood and rope and palmfrond mats. I think it can be fairly said that the voyaging ancestry of multihulls is a pedigree that goes much deeper into the past than many of the western monohull boats that we think of as “traditional.”

In a recent discussion on the yahoo group dwforum regarding traditional rigs, I was struck by something written by the New Zealand designer John Welsford, best known for his beautiful and rather traditional-looking small boats, of which hundreds have been built all over the world. He pointed out that low-aspect, traditional rigs like gaff, sprit, and lug had a couple of advantages over the tall skinny triangular sails of the conventional Bermudan rig that most folks think of when they picture a modern sailboat. If I understood him correctly, he was saying that if efficiency is measured on per-square-foot of sail area basis, Bermudan wins. If efficiency is measured on a heeling moment basis, the older quadrilateral rigs win.

I interpreted this to mean that the older rigs can carry more area, because their center of effort is lower. There’s not only more of it, when the wind pipes up, the boat can hang on to that area longer. The high-aspect ratio Bermudan rig has to reef sooner, which both lowers the aspect ratio and reduces sail area (and any advantage it might have.) John also pointed out that the proportionally greater chord of a low-aspect sail like gaff, lug, or sprit leads to greater latitude of trim on a reach– the low-aspect sail, like the low-aspect rudder, is not as quick to stall.

Other fine designers have done terrific work with traditional rigs. Michael Storer, for example, is a guru of the lug rig, as exemplified by his Goat Island Skiff, a handsome, simple, and fast open boat, and the graceful traditional-looking boats designed by Iain Oughtred would never look right with a modern rig, yet are both fast and handy, from all reports.

I wish I could say that any of that entered into my decision to put a sprit main on Slider– but it didn’t. I was cornered into choosing the rig. Or to put it another way, the boat chose the rig, not me.

I wanted a low-tech rig. I’m fascinated by the simplicity in use that characterizes some older rigs. I’m a particular fan of the junk rig, so much so that I once put a junk rig on an 11 foot dinghy. (It worked great.)

But as I explored the idea, I was confronted by three different objections, as it applied to Slider. One was weight aloft. A junk rig is heavy, with its yard, battens, and heavier free-standing mast. On a fine-hulled craft like Slider, excessive pitching due to too much weight aloft can be a serious flaw. Second, the boat would have had to put on some extra pounds, in the form of a tabernacle and struts, in addition to the heavier mast. Finally, someone online drew my attention to the fact that lug rigs like the junk were known to be slow in stays. Cats are also prone to that vice. Put the two together, and it might make the boat dangerously slow to tack. I reluctantly abandoned the junk rig idea.

The next idea up to bat was a balanced lug. I’d tried out a balanced lug on the dinghy, Sweet Potato, using a curved yard to approximate an elliptical planform. I clung to this notion for so long that I fixed Slider’s bulkheads and frames, and the location of her forebeam, based largely on the idea that I would put a big balanced lug on her. The rig is almost as simple to use as a junk, but is somewhat lighter, and doesn’t have quite as bad a reputation for slow-tacking as the junk.

The boat was half-built before I came to the dismal conclusion that the balanced lug was just too much for a boat like Slider– too much weight aloft– too much weight in general with the necessary stout tabernacle and struts. Plus a lot of that weight– the mast, the tabernacle, the struts– would be forward of midships and would tend to depress the bows, leading to increased weather helm.

No, I had to face reality. Unstayed rigs can make sense for monohulls and trimarans, where the structure of the boat can take the thrust of the mast. But out on the naked crossbeam of an open bridgedeck cat, it’s a lot less simple to arrange proper support for an unstayed mast. And it always adds weight.

In this case, I needed a stayed rig, because on a cat, such a rig is simpler and lighter. I’d have to resign myself to the complications of wires, and give up any hope of a lug rig, which is at its very best on an unstayed mast.

I wanted a workboat-like rig, as Slider’s lines are partly inspired by my admiration for the everyday beauty possessed by some old workboats (and the modern designs derived from them). To me that ruled out exotic rigs like the Oceanic crabclaw sail, or the lateen. I wanted something from the Western workboat tradition, since this was the underlying visual theme of the boat.

I also ruled out gaff rig, due to the weight aloft of a gaff, and the necessity for a taller heavier mast– though that may have been a mistake. Bernd Kohler, the well-known multihull designer, has developed a wishbone gaff that gives him very good control of his mainsail’s twist, using a vang to the gaff.

But I was thinking of traditional design, using wood, not carbon fiber, so I narrowed it down to two rigs– conventional fractional Bermudan, or sprit sloop.

I was pretty lucky, because when I went back to the drawing board, I found that the position of the forebeam was perfect for a Bermudan fractional rig. The position of the crossbeam and the position of the daggerboard case had already been finalized, so it was luck indeed. A person could transplant the rig of an O’Day Daysailer to Slider and it would be just about perfect, if it wasn’t too baggy.

On the other hand, a sprit-sloop rig would also fit the boat perfectly.

Temptation struck, and I was further tempted by the remembrance of an old article that I’d seen reproduced in various places on the web. It concerned a test carried out under a grant from a charitable organization interested in bettering the lives of subsistence fishermen. They wanted to assist these fishermen to acquire better boats, in which they could earn better livings, and so on. It somehow occurred to someone that while the conventional wisdom was that the Bermudan rig was superior in almost every way to older and less tech-intensive rigs such as gaff, lateen, and sprit, there was in actual fact no good test data to support the idea.

The organization arranged to use two identical 18 foot catamarans as test beds. One was rigged with a conventional (for the times) Bermudan rig. The other was rigged with each of the three archaic rigs, and then the two boats were sailed side by side to evaluate the differences in performance between the conventional rig and the old-fashioned low-tech rigs.

The surprising result was that the sprit rig was the best rig in that test. To windward, it was a staggering 30 per cent better than the conventional rig. It pointed higher and sailed faster.

You can see copies of the article’s pages here.

This caught my attention, because we live about 5 miles northwest of the nearest pass into the Gulf of Mexico, and on many summer afternoons, there’s a stiff breeze from the southeast. The need for good windward ability was, as a consequence, high on my list. I’d already fought my way through a morass of indecision regarding leeway prevention devices for Slider, finally deciding on a single deep daggerboard.

Of the major traditional rigs, the sprit has the lightest weight in spars, and the center of gravity is lowest. One of my most admired writers on design, the late great boatbuilder and designer Thomas Firth Jones (best known for his modest cruising multihulls) was a strong proponent of the sprit rig for small boats– and he’d had a positive experience with the sprit rig on a 23 foot catamaran.

With all this, and the tantalizing possibility of good windward performance from a cheap rig, I couldn’t resist.

It took me a while to figure out how to sail Slider– and how to put up the sprit with a minimum of bad words. But I now believe I made a lucky choice. The home-made polytarp mainsail, with its darts instead of broadseaming, gives decent performance at a fraction of the cost of a loft-made sail. Its effectiveness is most notable to windward, as the article indicated it might be. It’s even pretty good in light air, despite its modest area.

As I get to know the virtues of this simple, cheap, and handy rig, I feel less and less inclined to experiment with a conventional rig. I might someday, and I might even give Slider more area, just to see what she’ll do with more power.

But not any time soon.