Unisail for Solo Sailor?


Moondance Open 30

Van Gorkom Yacht Design LLC

Now that  you got rid of your crew, who is going to tack and trim the jib for you? Well maybe the answer is to get rid of your front sail altogether!!!

New technology in sails design and carbon free standing masts give a new lease of life to an old idea: the cat rigged racing boat.

The history of the cat-rigged sailboat, or “cat-boat” as they came to be known, dates back as far as 1840 when they were used for fishing and coastal transportation in and around the New England area. They were characterized by a single mast carried well forward, the virtues of this type of rig being simplicity and ease of handling. Around the turn of the 19th century, catboats were adapted for racing.

After all, the un-stayed rig idea is widely spread in the dinghy racing world (Laser I), so why not for keel boats?

So what exactly are the advantages of a cat rig with a free-standing mast? Modern free-standing rigs are inherently safer, far less complicated, cost effective, more aerodynamically efficient, and when paired with the right platform are able to match the performance of a conventionally rigged boat.Paradox_1050 - Van Gorkom Yacht Design LLC

Safer: Conventionally stayed rigs are held up by hundreds of little parts, any one of which could fail or slip resulting in a failure that could bring down the mast. A free-standing mast is held up by just two parts, the partners and the heel fitting – so the safety of the rig increases by the ratio of hundreds to 2. Failure in these areas is very unlikely if properly engineered, and can be easily inspected unlike a rigging connection at the top of a mast.

Less Complicated: The uni-sail has three trimming controls: the sheet, which is mounted at the very after end of the wish-bone boom and is controlled by winches port and starboard; a conventional cunningham arrangement lead back to the cockpit; and the choker which is a purchase system on the front of the boom that controls foot and leechtension, as well as mast bend. This serves to flatten and depower the sail in stronger wind conditions (not unlike a windsurfer rig). The uni-sail can be flown in breezes up to 25 knots without being reefed because the unstayed mast bends off in its upper sections with increasing wind pressure causing it to automatically unload. If it becomes necessary to reef, the sail has a conventional slab-reef system that is contained within lazy jacks supported by the wish-bone boom – so it becomes a one-man operation to lower and contain the sail. Because everything is so simple, there’s a lot less work to do so you don’t have to be a star athlete to sail the boat solo or double-handed. Yet, you can still maintain a very high level of performance. It also makes for far less stress when taking the family out for a Sunday cruise.

Cost Effective: The cat rigged Open30 has two sails……maybe three if you want a couple of spinnaker variations. So the cost of your sail inventory is cut dramatically, and with fewer strings to pull the deck hardware package is greatly simplified. While the mast will require more material to maintain the desired stiffness and bending characteristics, the heavier spar sections will be offset by not having spreaders, rigging terminals, standing rigging or chainplates. The wishbone boom is made from aluminum tubing and far less expensive than a conventional boom.

Aerodynamically Efficient: Free-standing rigs are more aerodynamically efficient because without wires, there is less windage (parasitic drag). In addition, the sail plan is no longer confined by the triangular shape defined by the fore and aft rigging. Because of induced drag the triangle is absolutely the worst possible planform for a lifting surface. Induced drag is a bi-product of lift, and although there are ways to manipulate it, it can never be totally eliminated. A working aerofoil, such as a wing, sail or keel, has a high pressure to windward and a low pressure to leeward and these are trying to equalize. In a triangular planform, the fluid flow on the high pressure side gets a chance to equalize sooner, by virtue of the shape (as opposed to a rectangular planform) by skewing up toward the tip and off the surface.  This skewing of flow from the high pressure side, mixing with the flow on the low pressure side, creates a tip vortex. The bigger the skew, the bigger the vortex, and the greater the induced drag. A way to reduce induced drag and increase the aerodynamic efficiency of the rig is to have either an elliptical or rectangular planform as there is little tendency for the flow to twist off into a large vortex with these shapes.  This is one of the main reasons for highly roached and square-topped mainsails on modern race boats. However, many of them place a great amount of importance on their running backstay systems to keep the rig up. Not so on a free-standing mast.

Comparable Performance: Cat-rigged boats have been stigmatized with a reputation for poor windward sailing capabilities and that was certainly the case with earlier designs. However, modern carbon fiber cat rigs are strong, light, aerodynamically efficient, and are able to carry a comparable amount of up-wind sail area to a conventional sloop. Between the incredible advancements in sail technology and not having a backstay to worry about, the roach of the sail can be fairly generous with full length battens to support it, creating a highly efficient airfoil.  Couple this with modern sailboat design philosophies, and the result is a vessel every bit as capable of hanging with the fleet on a beat to the windward mark. The off-the-wind performance of the cat rig is just as impressive and maybe more so. The area of the unisail alone, which can be adjusted to an extremely full shape, is more than enough for a great downwind ride, and very easily handled. To complement and enhance the reaching performance, the spar on the Open30 has been engineered to allow for a fractional asymmetric spinnaker to be flown from a deck-mounted, retractable bowsprit that can be articulated 35 degrees to port or starboard.


American boat builder Wyliecat
has taken the lead in producing unisail performance boats which, apparently, are competitive under the local PHRF handicap system but have built a sufficient following to have their own one design class in the Bay of San Francisco.
Wyliecat 30
“…The Wyliecat 30 was conceived with the premise that performance sailing doesn’t need to be complicated to be fast and fun. Combining state-of-the-art technology with the time-proven cat rig, the Wyliecat’s performance needs to be experienced to be believed…”

Elsewhere, in Australia, a 12m performance oreinted yacht (Radford Yach Design) was recently launched boasting a similar unisail and wishbone set up. The programme is short-handed offshore racing, fully crewed racing in the bay of Sydney as well as family cruising…
Food for thoughts…

I leave you with a video of some smooth tacks with the Wyliecats: http://www.wyliecat.com/latest_news/vids/WYLIE%2030_320x180_h.264.mov

Links / references:
http://www.sponbergyachtdesign.com/StateoftheArt.htm (Good article on free standing mast technology and efficient sail shapes)
http://www.vgyd.com/Catrig.html
(Van Gorkom Yacht Design)
http://www.wyliecat.com (Wyliecat Boats homepage)

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