Wing Sails for Small Watercraft such as Kayaks, Canoes and Multihulls
Is this for You?
In this post I’m going to introduce the concept of wing sails for small watercraft, perhaps something you can implement for yourself on a kayak, canoe or perhaps an outrigger canoe. This first post in the series will provide a general introduction. I’ll go deeper into technical details in future.
Backstory
The wing sail is a concept that captured my imagination decades ago, ever since I first learned how to sail a dinghy in the Singapore harbor at age 11, that’s 49 years ago.
I’d always been fascinated with the power of the wind and ways to harness it with technology for transforming it into useful driving thrust through sailing rigs, especially rigs based on airfoils.
I also developed a fascination with flight, the design of aircraft wings, ultralight hang gliders and any kind of craft that would let you to explore uncharted wilderness on your own terms while simultaneously harnessing the power of the elements.
More recently, I stumbled upon a Swedish website (https://sites.google.com/site/icewinghomepage/) by Anders Ansar, who’d developed the Ice Wing. The Ice Wing is a hollow, vertical airfoil. You stand inside it. Think of it as a personal wraparound wing. Straps suspend it from your shoulders as you lean into the wind. The lift created by the Ice Wing allows you to skate across the vast areas of frozen smooth ice of the Baltic Sea at record speeds. Ansar Anders was able to set some pretty incredible speed records for ice sailing with his innovative Ice Wing.
Another wing sail that caught my attention was described in a post I found on the Australian Kayak Fishing Forum, by Goanywhere: “Is this Australia’s first Kayak Wingsail?” (https://www.akff.net/threads/is-this-australias-first-kayak-wingsail.46609/#post-482345)
Goanywhere provided a detailed description of how he built a wing sail for his sit-on-top kayak. For the primary construction materials, he used poly tarp, paracord, aluminum tubing, PVC pipe, closed cell foam sheet and closed cell foam pool noodles. Briefly, he suspended the pool noodles on a harp-like frame built from PVC pipe, aluminum tubing and paracord. This frame provided the mechanical support and the space filling “body” for his aerofoil. Then he wrapped the frame with foam sheets and polytarp to complete the sail. His result was a remarkably aerodynamic wing sail, that allowed him to sail very close to the wind, with very little drag, using a very small sail area,
What caught my attention about Goanywhere’s wing sail was rather than furl the sail after setting anchor fish, he simply let it luff in the wind. This worked well even in a fairly fresh breeze. Moreover, he was able to get to his fishing spots rapidly and efficiently in his kayak.
In other news, I’ve experimented with poly tarp sails of conventional design, specifically a simple lug sail that I fitted to a diy outrigger sailing canoe. I sailed it on a reservoir in the prairie region of Minnesota. I had great fun and I was able to drive my little outrigger canoe craft to tremendous speeds. But with a lug sail, I was never able to sail very close to the wind. This limitation turned out to be quite frustrating because there were a set of narrows on the reservoir that I wasn’t able to navigate past to get to the main body of water.
To clear that hurdle, I decided to build my own pool noodle noodle sail. My project is pretty much based on Goanywhere’s (Australian kayak fishing forum) but with a couple of twists,
Theory of Lift
There are two main schools of thought for how aerofoils generate lift:
According to both, you need an aerodynamic, teardrop shape that offers minimal drag. Minimal drag means that the sail will be more efficient and sail closer to the wind. The teardrop design will peacefully weathervane when allowed to luff instead snapping and flapping like sails made from thin, single sheets of fabric.
Beginning with a teardrop cross section, you can add things like camber and angle of attack to generate lift.
One school explains airfoil lift in terms of the Bernoulli effect whereby air on one side of the airfoil flows faster over the surface than on the other side. The resulting difference in surface pressure accounts for lift. The upshot of this school is that the air stream distance on one side of the wing needs to be longer than on the opposite side. To create this difference, you can design a thick, asymmetric airfoil. The pool noodle design relies on pool noodles and foam sheets to create a thick sail. The wind helps to shape the airfoil by flattening its windward side, while billowing out its leeward side.
The other school purports that an airfoil generates lift by deflecting the airstream. By Newton’s principle of opposite and equal reaction, deflecting the air in one direction imparts lift on the airfoil in the opposite direction. This school goes far deeper into the nuance of momentum transfer, the Cut Off principle, circulation around the airfoil, et cetera. In the interests of brevity I’ll leave that for another article. The deflection/momentum school teaches that in order to create lift, you need to be able to change the angle of attack and the camber of the airfoil. You can do both in a number of ways. For example, you can fit the airfoil with adjustable flaps on its leading and trailing edges. With the pool noodle sail, the whole airfoil flexes in the wind as you sheet it in, while it pivots about its mast, to alter both its camber and its angle of attack.
Design Details
In my case, I wanted something that is economical and easy to construct out of readily available materials, so materials like PVC pipe, pool noodles, paracord, and polytarp really fit my bill.
The design should also allow a certain degree of flexibility, i.e. be amenable to quick modification and correction. Again, the pool noodle concept really fits the bill.
A semi-rigid airfoil that can reverse its camber is also ideal. What I wanted was an airfoil that self-cambered on either tack to create more lift.
The alternative to self-cambering is to resort to flaps. I had entertained that but decided on leaving that for a future project.
Yet another design consideration was to create a hybrid between a thick airfoil and a thin sail. In other words, the leading section of the wing sail would be thick, with a certain degree of camber, but the trailing edge could be extended into a membrane sail. I wasn’t too keen on this concept but I wanted to leave it open as a possibility.
The final design concept I wanted to keep in mind had to do with traction kites, for example those used for kite sailing and hydrofoil surfing with inflatable wing sails.
I think it’s worthwhile to look closely at inflatable wing sail technology that’s really blossomed recently.
The main advantage of a wing sail with respect to a conventional sail, is that you can develop a lot more lift with a much smaller sail area, and with a much smaller amount of drag. This means it can sail closer to the wind. Closer to the wind is where a wing sail can really excel. It gives you the crucial advantage of weatherliness.
A wing sail also provides the benefit of being able to peacefully weathervane without the need to furl or stow the sail below decks when moored, beached or at anchor, simply by virtue of the small amount of drag that a wing sail develops and its freedom from the violent snapping and flapping of a membrane sail.
Moreover, a wing cell is remarkably simple. It can even be set up to be self-trimming, with the addition of a small area airfoil rig to keep it at an optimal angle of attack. But that is the subject of a whole different article and a whole new project that I will hopefully get to within the next couple of months.
For the moment I’m going to focus on rigging my sit on top plastic Pelican kayak with an outrigger for stability, a dagger board for tracking, and a rudder for steerage, so that I can mount a wing sail on a simple cross bar, so I can test it out the pool noodle wing sail concept on either the waters of San Francisco Bay, Bodega Bay or Tomales Bay here in Northern California.
Interested in equipping your kayak with a wing sail?
I recommend you first look at the pool noodle design published by Goanywhere on the Australian Kayak Fishing Forum. (https://www.akff.net/threads/is-this-australias-first-kayak-wingsail.46609/#post-482345)
Also take careful look at the designs published by Ansar Anders on his Ice Wing homepage. (https://sites.google.com/site/icewinghomepage/)
More Info on wingsail design and airfoils
Theory of Wing Sections (https://aeroknowledge77.files.wordpress.com/2011/09/58986488-theory-of-wing-sections-including-a-summary-of-airfoil-data.pdf)
Look at the flip tacker design. It provides an ingenious way of using a rigid airfoil on a small craft.
Also take a look the rigid, flapped designs for wingsails seen on the latest contenders for America’s Cup.
Also look into self-trimming wingsail rigs:
Peter Worsley – Wingsail Experiments -Article https://www.sailwings.net/article.html
Self trimming wingsail – the pulley/cord control system. https://www.sailwings.net/pulleycord.html
Design of a free-rotating wing sailfor an autonomous sailboat http://www.diva-portal.org/smash/get/diva2:1145351/FULLTEXT01.pdf
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And stay tuned for my next blog post on my own pool noodle project. Until then Happy sailing and thanks for reading.