BUILDING A CANOE SEAT THAT SUPPORTS A MAST

This article originally appeared in the Jan/Feb 2003 issue of Small Craft Advisor. It introduced a series on "Seeking the Perfect Small Craft Rig."

The thirty year old seats in my Old Town canoe finally gave up the ghost. No doubt sunlight was the culprit; turning the flexible plastic coating into a brittle one. The surface cracked open, exposing the foam flotation which gradually chafed away. Reluctant as I always am to undertake boat maintenance/renovation projects, inaction was no longer an option. Something had to be done.

The sorry state of my gear provided the impetus to replace both seats with wooden ones, integrating a maststep and partner into each. Masts of varying heights could then be mounted in one of two (if not both) locations. This was done, in part, to mollify my canoe who was undergoing a midlife crisis. For some time, she had been nagging me to help her fulfill a life-long ambition. She had long yearned to give her hull to science and to become a full-fledged research vessel. She wanted to be able to test "a vast array of rigs"--her words not mine--in order to determine finally and definitively: which rig would yield the best propulsion for a small craft. I tried to point out to my canoe that she might not be the ideal boat for the job; that testing a "vast array" of rigs might require something more or better than half-vast equipment. But she remained adamant, claiming that her new facelift would qualify her completely. With the means thus available for a ambitious rig research project, all that was lacking was the reason for doing it.

Tradeoffs and compromises in rigs

A number of service industry businesses display a sign that reads: "Speed, quality, economy. Pick two." A rig designer faces a similar dilemma since, ultimately, any sailing rig is a compromise struck among three ideals: 1) performance, 2) convenience and safety, and 3) economy. It is relatively easy to achieve two of the ideals; virtually impossible to meet all three criteria in the same rig. A high performance racing rig, for example, can be made to operate with a modicum of convenience and safety, but it will not come cheap. Likewise, a seaworthy, time-tested, rig built with inexpensive, off-the-shelf materials, will get you to your destination, but never at the head of the pack.

Sporadically, over the next several issues, I propose evaluating different rigs in terms of how well each one meets the three stated ideals. Where and to what degree does a given rig succeed? Where does it fall short? How does it achieve its success and what does it tradeoff in the process? Tentatively, I plan to consider: a lateen, a lug rig with particular attention to a standing lug of high-aspect ratio, perhaps a windsurfer sail or a low-tech version thereof, and a gaff rig. I hope, along the way, to stimulate discussion among, and to solicit suggestions from SCA readers on the topic.

In all likelihood, most sailors consider the question closed; long since resolved in favor of the Bermudian sloop rig. Indeed, the standard Bermudian rig, consisting of a jib and a jib-headed or triangular mainsail, has been the rig-of-choice for small yacht owners throughout the last century. Its popularity is likely attributable to its success on the racing circuit. Yet naval architect and historian Howard Chapelle has argued that its popularity is undeserved. The rig, he maintains in Yacht Designing, had long been known to builders of commercial sailcraft. Working skippers, however, rejected it in preference to other rigs. Chapelle recommended, instead, a sailplan similar to a West Wright Potter's, an arrangement which, he argued, would deliver greater thrust on a significantly shorter mast. A rig, in his estimation, much better suited to bringing home the bacon--or oysters or lumber, for that matter.

Unquestionably, the Bermudian rig has its virtues. And because of its popularity, these virtues have been systematically exploited and developed. It may be the most weatherly of all rigs--though there is some dispute on that point. It is certainly easy to use; sheeting, roller-reefing and roller furling systems have all been carefully refined to that end. Against that, however, the rig has some notable deficiencies. The mast is tall relative to the sail area, putting more weight aloft than is ideal. If one chooses to reduce the mast section at the peak, he is forced to add stays which increase the total windage. The top 5-10% of a triangular mainsail is largely ineffective because of the wind shadow of the mast and the tiny amount of sail area that receives undisturbed air. Not to mention the inevitable power loss at the tip of a foil. For the jib to be effective, the forestay must be kept taut, which means that all stays must be torqued down to ensure that. The mast becomes a compression strut which has to handle loads of up to twice the boat=s displacement. The keel, mast step, chain plates, or bridgedeck, in the case of a catamaran, must all be reinforced to contend with such loads. In order to be properly sheeted, Bermudian rigs typically involve hardware; blocks and winches. To eliminate sail twist, a vang or kicking strap is required. The entire package ends up relatively complex and expensive. Because the various parts are interdependent, the integrity of the rig depends upon the integrity of its individual components. On some boats, if a single stay fails, the mast can topple. Off the wind, a Bermudian rig will not provide speed of a lower-aspect rig like a gaff or lug rig. Often shrouds prevent the main from being fully boomed out. On a run, the jib is likely to be backwinded, becoming completely ineffectual. To be competitive on a run, the Bermudian skipper will need a spinnaker with all the additional rigging, paraphernalia and crew that this finicky sail entails. Though unarguably good, the Bermudian rig is far from perfect.

What, then, should we be looking for? The following are more explicit criteria by which to compare and judge rigs.

Naturally, we will want our perfect rig to provide good performance. Square foot per square foot, it should be effective in converting side pressure into forward thrust. It should minimize heeling moment. In theory and in the lab, different sails are deemed differentially efficient. A jib, for example, is thought to offer superior performance per square foot than the typical mainsail. And some theorists hold that the traditional South Pacific crab claw lateen is the most efficient sail of all.

In the field, however, such differences are much harder to demonstrate with any consistency. Furthermore, small differences in rig efficiencies may be somewhat irrelevant. The skipper who can instantly increase sail area to take advantage of changing wind conditions does not need to be overly concerned with thrust per square foot. If the wind drops, he piles on more canvas; his speed limited only by how much sail is at his disposal. The ability to quickly change the size of a rig, then, can easily compensate for a minor deficit in efficiency. Nevertheless, we will keep an open mind on the subject of efficiency, dutifully noting all of a rig's alleged performance enhancing features as well as those characteristics that are thought to impair performance.
We will also seek a weatherly rig. In theory, a single full-sized sail is more weatherly than two half-sized sails. A single sail can be sheeted into an angle of about five degrees off the centerline. On the other hand, a jib sheeted so hard is likely to spoil the airflow around the main.

As a result, a jib can rarely be sheeted to an angle closer than ten degrees. On paper, therefore, a catboat can point higher than a sloop. In practice, however, this too is hard to prove. Still, since a single sail is more convenient to use than two, and more economical, we will assume the fewer sails our perfect rig has, the better.

For weatherliness, our ideal would be a tall, high-aspect rig; something in the four- or five-to-one range would be optimal. But off the wind, we would prefer something closer to an aspect ratio of two to one or less. The ideal, of course, would be a sail whose aspect ratio can be instantly changed as course is altered. Unfortunately, no such thing exists. But if it did, we would want it.

For convenience and safety we would like our spars to be as short as possible. In fact, we would like to dispense with a boom entirely if we could be sure performance would not suffer seriously. Or, possibly, could we substitute a light, flexible batten for the boom? We will be looking for a light mast with a high strength-to-weight ratio; a mast that can be quickly and easily stepped. Similarly, we will want to be able to shorten sail quickly and easily. A number of other hypothetical issues crop up under the "convenience and safety" rubric. Are some rigs more forgiving than others, or adaptable to a wider range of conditions? Are some rigs better able to weather a sudden gust; becoming automatically self-reefing in effect? Are some more amenable to self-steering than others? When course is altered, do rigs differ on how drastically helm balance shifts? Do they differ in the degree to which heeling affects helm balance? Are some rigs inherently more docile than others? (A useful dimension that Philip Bolger introduces in 101 Small Boat Rigs.)

Our ideal rig would be portable. We would like it to form a nice compact, storable package.

Battens pose a particular dilemma, particularly full-length ones. On the one hand, they're a pain; they can catch on a stay or shroud, they create chafe points which reduce the sail's longevity. In order to furl a sail, battens may have to be removed entirely. On the other hand, their benefits are manifest. Battens allow sail makers to add area in the sail's head, which, in turn, allows that part of the sail to contribute thrust. Battens prevent the sail's leech from fluttering, a condition that robs the sail of so much force. And battens can control the camber of the sail, ensuring that the sail will take and hold its desired shape. Consequently, we are reluctant to rule out the use of battens entirely in our ideal rig. But I propose, tentatively, that we limit our rig to one batten. One batten should give us the expected benefits at an acceptable cost to our other criteria. Zero, of course, would be preferable.
To ensure the economy of our rig, we will look for little or no standing rigging. Stainless steel stays, turnbuckles, swages, pad eyes, and tangs all drive up the cost of a rig; the "boating" or "marine supplies" label seems to automatically double an item=s price. These items also increase a rig's complexity while increasing the points where a rig can fail. State-of-the art blocks and winches carry astronomical prices. We will, accordingly, look for a rigs that do not require them; rigs that seek to balance, somehow, the forces and stresses that are generated.

Skeptics who doubt that one's choice of rig can put even a small dent in the overall cost of sailing should take heed: Moth skippers (SCA #16) estimate that their seventy-five square foot cat rig--including mast, boom, sail, hardware and rigging--represents almost half of their total investment. Certainly, the largest, most expensive item in any rig is the sail. But a rig design that lends itself to the amateur sailmaker, using alternative sail fabric, can save the boat owner a bundle. Somewhere along the way I will discuss alternative sail materials and sailmaking procedures, suitable for both the non-dexterous and the sewing-machine-challenged.

Converting an Obstinate Canoe to a Full-Fledged Research Vessel

The original sailplan for my canoe, developed six years ago, featured a lateen mounted on a short, bipod mast. Ideal as the mast may have been for the sail, it would have been very confining to a canoe whose stated ambition is to test a vast array of rigs. Hence the need for new mast partners (along with the new seats) and an adjustable leeboard.

One important consideration imposed on the seat design: I did not want the new mast brackets to interfere in anyway with paddling the canoe once the mast was removed. I didn't want sharp edges projecting forward where they might snag or chafe a paddler's leg. I didn't want them to project upward where they might snag an even more sensitive part of the anatomy. Consequently, the use of hinges was rejected. A second consideration: I didn't want to have to drill a hole or holes through my hull to accommodate fasteners with which to hold a maststep in place. The mere thought of compromising a hull's integrity by drilling holes below its waterline leaves me in a physically weakened state.

I designed and built the forward seat first. I have used it for approximately fifty hours; experimenting with three different masts and five different rigs. The stern seat came later. Though its design is probably better, so far it remains an untested, unknown quantity.

In both cases, I started by building a sealed box, using three-eighths-inch plywood. I mitered all edges to provide for a larger gluing surface. Small screws held the six panels in place temporarily. I joined the four sides with epoxy, and then epoxyed the top and bottom panels in place. Once the epoxy set up, I removed the temporary screws and filled the holes with epoxy. This plywood box serves both as a sealed flotation chamber and as a structural element; a box beam, in essence.

For the bow seat, a second 3/8" ply panel, cut to the shape of the old seat, was epoxyed to the top panel of the flotation chamber. From one-by material, I ripped two strips: 3/4" x 1" x 10".These were screwed and epoxyed in place as indicated in the diagram. Epoxy fillets were added along the joints to ensure that these cleats would have sufficient strength to prevent the mast from moving side-to-side. The former plastic seat had been held to the underside of the gunnels by four stainless steel bolts. I simply reused the bolts, passing them through the existing holes in the gunnels. Fore and aft movement of the mast is prevented by a ten foot length of 3/8" braided nylon line. I tie a bowline in one end. The loop thus created remains temporarily on the top of the seat. The free end of the line proceeds down the after side of the seat and forward underneath the seat. It wraps around the base of the mast, passes underneath the seat again, then up. It proceeds forward, around the mast, then back through the bowline. The free end is pulled tight. A half hitch or two will keep the line (and the mast) in place.(diagram) It is possible to exert a tremendous amount of force using this technique; if your knots are good, your mast is secure. If not the most convenient method of stepping a mast, it is unequaled for reliability and cost-effectiveness.

Mast Partners Diagram (PDF)

In retrospect, what would I do differently? 1) The top, trapezoid-shaped panel should be cut from 3/4" ply rather than 3/8". 2) The side cleats should be ripped from two-by stock rather than one-by material to furnish a larger gluing surface. 3) The cautious, safety-conscious builder will want to fill the flotation chamber with foam to ensure its performance. I had considered doing this at the outset, but I have an unfortunate habit of erring on the side of frugality, hesitating to invest too heavily in something that may not work.

The back seat differs only slightly. The top trapezoidal panel is wider (fore and aft) to allow for a two-inch-square hole aft of the flotation box. This seat has a second bottom panel epoxyed to the flotation chamber. The bottom panel has a similar two inch hole. The mast passes down through the two holes and lodges against the plywood flotation chamber. Once the mast is in place, a dowel, or a cotter pin of some sort is installed directly below the top panel. This will prevent the mast from popping free following a capsize. If your rig design calls for a mast stepped close to the bow, you would use the mast in this location. What is normally the stern of your canoe would become the bow.

To properly evaluate a rig, the centerboard (leeboard, or dagger board) must be properly positioned relative to the sail's Center of Effort. If the board is too far forward, the boat has a tendency to luff up. The board will then stall, the boat will slide leeward, and forward progress will come to a virtual stand-still. If the board is too far aft, the boat will not point properly and will not want to come about. What appears to be a defect in the rig, may, in fact, only reflect the improper positioning of the board. I therefore developed a leeboard that would hang from the gunnel. It was capable of sliding fore and aft to produce the desired helm balance. I made only one board which, as a consequence, must move from port to starboard when changing tacks. Changing tacks, the forward edge of the board becomes the trailing edge and vice-versa. The board, therefore, is symmetrical (fore and aft) around a vertical axis running down its center. I assembled my leeboard from cedar one-by-six, a piece of sheet metal (heavy gauge roof flashing), and a one-foot length of 3" PVC pipe. To minimize water resistance, I beveled the edges of the one-by-six below the waterline. I nailed and glued the sheet metal to the outboard side of the one-by-six, and bolted the PVC pipe to the inboard side. Prior to that, using a circular saw, I had cut and removed a two-inch longitudinal slice of the pipe. This allowed the PVC to slide down and clutch the gunnel. Mounted on the lee rail, the board receives pressure pushing inboard. This pressure effectively locks the PVC and the leeboard in place.

LEEBOARD DIAGRAMS (PDF)

This leeboard design is adequate to its task, but only adequate. Because of its light weight, the leeboard has an annoying tendency to lift off of the gunnel once side pressure is removed. Upwind it works fine. Off the wind, however, the would-be researcher will want a lanyard that runs between the leeboard and canoe, lest his leeboard lift free from the gunnel and disappear into the wake, leaving him piloting a sailboat that is incapable of going to windward. If one is considering designing and building a boat, a leeboard of this type would be a good interim solution to determine the proper and permanent location for a board.

Philip Bolger (Boats win an Open Mind) suggests a slightly different model for a gunnel-hung leeboard. But his enlarged clothespin design has some apparent liabilities of its own. The apparatus is bulky, appears heavy, and looks as if it would interfere with the operation of a low hanging sail. In his defense (and mine, too): because of the stresses imposed upon a leeboard--certainly enough to crush a carelessly placed finger--designing a temporary and moveable version is no mean trick. If anyone out there has come up with a satisfactory solution, I hope they will share it with the rest of us. Similarly, if anyone has suggestions on the perfect rig, alternative sailmaking materials, alternative materials or techniques for spar construction, please pass them along, too.

The objective of this whole, on-going exercise--besides offering endless hours of entertainment and self-fulfillment to my stubborn, implacable canoe--is not to try to start a wholesale rig conversion movement. Few readers will experience a sudden, overwhelming urge to take a chainsaw and bolt cutter to their rig. You should, however, be able to achieve a better understanding of your own rig, how to tweak it or tinker with it, and perhaps how to set up a jury rig to get you back to port. Plus, if you do experience a sudden, overwhelming urge to build a daysailor, or if find yourself suddenly in possession of a canoe undergoing a midlife crisis, you'll be able to respond promptly.