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by Philip Frohne - Hazelwood, Missouri - USA

Want to have the coolest looking boat on the lake? Show off your high tech building skills with a rigid wing sail that will make any America's Cup fan envious. Needing a winter project, I combined my model airplane and boat building knowledge into a ten foot tall by 4 foot wide hard sail using common hardware store materials. By avoiding both carbon fiber and epoxy, I kept the price around $50. Being a private pilot and graduate of an aeronautical college, I wasn't going about this project totally clueless. I opted to keep the prototype simple and not hinge it with contour changing flaps, slats, or slots (yet). I wasn't sure I could finish it, or even transport it to the lake in the back of my pickup truck without damaging it.

The build was half the fun. For starters, I chose the same airfoil most of us attempt to use on our rudders; the NACA 0012. I found the loft dimensions for the airfoil on-line, and scaled them onto a four foot long paper pattern. These were then transferred to a 4'x8' sheet of 1 inch construction foam insulation. Cost of the foam sheet was about $15. By overlapping the ribs front to back, there is easily enough material for 2 wing/sails. Even though I had access to a hot wire cutter, it was quicker and easier to cut out the ribs using a fine toothed saber-saw, then sanding with 100 grit paper. Foam is very easy to work with. The top and bottom ribs were skinned in 1/16" plywood (TB-III glue) for strength.


I slip it onto a Sunfish mast; a 2.25" diameter by 10' aluminum tube. Three sets of mast holes were drilled into the ribs, one at the center of pressure (lift) and 2 on either side for experimental purposes. Three feet of duck-under room was created by plywood doubling the appropriate rib hole for the mast to rest and pivot on. No downhaul was used. This is a nine pound wing for those concerned about leverage moment arms and tipping. Theoretically, the airfoil will have less air drag than the plain round mast, so allowing it to weather-vane should prevent most tip-over worries.

Twenty-four ribs were easily made in half a day. Slots were made in each for a pair of 1" x 0.25" x 10' pine stringers by drilling three 0.25" holes side by side, then cleaned up using a 10" mill bastard file. The ribs were then strung six inches apart and bonded with Gorilla glue. The location of the stringers isn't critical. In hindsight, the ribs could have been spaced a foot or more apart, allowing for a slightly lighter structure, and a faster build. A 1/16" plywood "X" shaped stub mast (main spar) supports the section above the aluminum mast in one of the alternate sets of mast holes.

If I have lost you, just look at the pictures. It's far from rocket science. The leading (LE) and trailing (TE) edges are simply Duck TapeT ala Mythbusters. Try to keep the surfaces smooth. Three overlapping strips on the LE, and one on each side of the TE is enough. The covering material came from 2 large packages of 3M heat shrink window insulation film. That's another $15. It was attached to the four outer edges using 2" wide clear packing tape. I bought extra double sided tape to stick the film to every rib as well. (On Piper Cubs, the fabric covering is sewn to each rib.) The strings in the pictures mimic airplane drag/anti-drag wires. I was hoping to reduce any twist and assure that all the bits would stay together in a catastrophic failure. It wasn't worth the bother. The wing is now complete except for some spiffy colored and checkerboard tape, and number decals. Looking cool is 50% of the effort.

I transported the wing to the lake on top of my Uncle Johns Skiff in the back of my pickup. The wind plasters it down to the boat gunwales and it rides along at highway speeds just fine. Two people are required to hang onto it though once at the boat ramp and exposed to the wind. It's a handful. Keep it pointed edge into the wind because it wants to fly. The mast is slid into the bottom rib until it hits the stop rib. Then by keeping the top of the wing facing into the wind, and allowing it to weather-vane as it is brought to vertical, it can be stepped into the boat. Do this when no one is looking.

The first day I tested the wing, there was no wind and I simply drifted into the middle of the lake. The second day I tried it, there was too much wind and a gust pick up the boat and knocked it over on the launch ramp, a testament to the strength of my mast step and dispelling the "less drag then the bare mast" theory. The third day, a tornado damaged my house. Fearful of any fourth attempt, I dry sailed it a couple times on the front lawn. Contrary to the extreme flimsiness, there is absolutely no twisting in any amount of wind. And as far as strength, I have yet to accidentally puncture the skin or break any internal bits & pieces, even after the wind tried to double it in half a couple times while off the mast.

I finally found a decent 6-8 mph wind day on a 2,400 acre oxbow lake that is silting in at 4 feet deep (great waves though). After rowing out, I attached a sheet to both ends of the bottom rib for control. There is no conventional 'feel' to a wing sail, so the only way to point it is to watch a wind vane attached to the stub mast. The wind vane rocked with the boat and wasn't a lot of help. The wing also had a tendency to flop long its center of gravity if both sheets were not held firm. I haven't tried the mast in one of the alternate holes yet. But once pointed into a direction that moved the boat (speed measured by calendar, not GPS), some conventional handling pressure could be felt.

Unfortunately for aerodynamic theory, the wing was at a negative angle of incidence when propelling the boat! The NACA 0012 generates lift between just 12 and 15 degrees to the apparent wind, not much margin. So as a rigid sailboat sail, it's the wrong airfoil without adding lift devices (flaps, slats, slots, jibs, etc.). Once we put on the usual Sunfish Mach II lateen sail, we rocketed up and down the lake at a blistering 2.5 to 5 knots like always (eighth season sailing this fun flatiron skiff).

At this point, I'll probably let my son try to hang-glide it off a small hill. I sailed on Dennis Conner's Stars & Stripes 12 meter yacht (#56) in Cozumel Mexico last fall. I learned that when the wind isn't blowing, all sailboats handle exactly the same. The rigid wing sail is no exception, but it looks a whole lot cooler than a conventional polytarp sail!

Phil Frohne

Uncle Johns Skiff, 1974 Chrysler Buccaneer, Catyak

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