Canting Keel, DSS and Dynamic Control

Canting Keel

Jonithan McKeeCenterboard, swing keel, or keel, new monohull sail boat purchasers should at least consider vessels like Sadlers, Potters, Etaps and MacGregors that have solid flotation. They should also choose thin rather than wide monohulls. The thinner the hull, the more it is like a log in that it is self righting and of course the quicker the righting the less likely serious flooding. Such vessels, in the hands of competent crew, are the most seaworthy. Note – some ocean racers are wide rather than thin. This is the result of artificial limitations on design, like maximum water ballast and experimentation with canting keels that if canted to the wrong side could cause capsize quickly in a thin hull. Without these design rules the vessels would be thinner. Since 20012 experiments with a replacement for a bulb keel (canting or otherwise) have been successful and in 2014 Dynamic Stability was shown better because the drag caused by the surface area of a bulb is eliminated when the bulb is eliminated.  Even wide canting keeled racers such as the stretch Volvo 70 Maxi Comanche, present a thin form to the water when heeled modestly. It is the surface area of the bulb itself that makes them slower when there isn’t enough wind to bring the competitors to hull speed.

In November of 2003, I finally caught up with one of the McKee Tasar crew at a South Sound Sailing Society membership meeting.

Jonathan McKee keeps himself on the edge of sailing technology which in 2003 meant canting keels, which he prefers to call swing keels. I think the swing term should be reserved for technology advanced by MacGregor Yachts and hence will stick with canting keel as the descriptor. An advocate for canting keels, McKee was active in a project that in 2004 produced a vessel called Genuine Risk (GR) running out of San Diego. That ship is a 94 foot “no compromise” ocean racer showcasing the canting keel technology.

Obvious once you become aware is that a canting keel does not provide lateral resistance. This implies that vessels using this technology will do poorly upwind. The fix on GR was a forward rudder.

In 2004 water ballast and canting keel technologies started being described as kinds of movable ballast. The term movable ballast applies to both boats. Fortunately, in March of 2004, Sail magazine on page 110 proposed that canting keels are a superior form of movable ballast. The author was unaware that artificial limitations, discussed above, had encouraged some ocean racing designers to build wide water ballasted vessels.

“Wide boats with water ballast are very effective at generating stability at low angles of heel, but they are prone to capsize and are too stable when inverted; they can stay turtled indefinitely….A moveable keel can be an effective tool when righting a turtled boat.”

Water ballasted boats need not be wide and the Mac26x is not prone to capsize. She is also self righting. To be fair, the author did note many of the canting compromises. These include loss of lateral resistance which limits sailing to downwind, the T-bulb configuration which is a “classic trap for crab pots and weed”, and that canting technology is a rather expensive way to increase stability. With these one should add that canting keel vessels once capsized can sink and that the bulb on the fin is a large source of drag. Furthermore, I have yet to find a canting keel vessel that does not have an opening in the hull through which water can enter. They are severely limited on the interior because of the mechanisms necessary for the technology. Then there is the weight. Water ballast is moved off the boat in light wind. This advantage is significant especially in doldrums.

I have concluded that patent holders were high on the canting technology but sailors need have been.  Of course it would not be difficult to add something like the CBTF canting bulb used by the Shock 40 to a mac26x. The forward foil is already in the correct position and a well for the canting mechanism could be added without modifying the ballast tank because the components for the tank are far from center line. But I think water ballast superior.

A group of keel boater’s peppering McKee at a sailing society meeting about Mini-Transat racing couldn’t help vocalizing how similar McKee’s mini boat looks to a Macgregor 26 (x). Sailing Society mates later confirmed that I had heard the comment. It pleased me very much. I have no idea who made the comment but it was a highlight of the evening. You lift a rudder on the mini’s just like you are instructed by the manuals to do with a Mac26x. McKee was encouraged to admit that he prefers sailboats that plane and mono hulls over keel boats and multhulls. He reluctantly noted that his favorite boat is an Ozi 18? and couldn’t help himself from commenting on a grounding incident a new-to-our-society keel boater had that weekend while returning from a race (no damage fortunately). As an aside – it is now possible to have pizza delivered to a grounded vessel – this owing to cell phone and gps technology. The mini-transat boats are half the weight of a Mac26x unballasted. Owing to a “Box” rule they have become wide over the years but can not be more than 22 feet long. Stability comes from the wide beam but more from moving solid weight – gear, water, food etc – to the windward side, according to McKee. Any sail plan is allowed within the box rule.

In sufficient seas all boats can capsize. Today small racing and ocean cruising sailboats, similar to Mac26x vessels, are rigged to withstand capsizing, the most seaworthy righting themselves quickly, like a log, rigging undamaged. This is in contrast to vessels prior to the 1970s where solid ballast was added in amounts so large that the boats would sink when flooded. Solid ballast weight even today is mistakenly believed to be better insurance against capsize than water ballast.

Charlie McKee was appointed high-performance director of the U.S. Olympic sailing program in 2012, three months after the United States failed to win a medal in a sailing competition This had not happened since the 1936 Berlin Games.

McKee won the bronze medal in the 470 class in the 1988 Olympics with John Shadden and the bronze in the 49er in 2000 with his brother, Jonathan (pictured above.)  He also coached the U.S. windsurfers in 1992; Michael Gebhardt won silver.

Dynamic Stability Systems

Like Canting Keel technology, Dynamic Stability technology is highly favored by the patent holders. However, sailors do need to take note of it because it is technology used by rowing craft, like Viking long boats and crew shells. In its pure form (the form used by Wild Oats in the 2014 Sydney Hobart) foils not unlike oars are extended on the leeward sided to hold the boat from healing further.

shell at east end of

Montlake Cut

Opening Day 2002Rowing looks gentle, like sailing, but there is a certain violence and a definite acceleration involved at the start of a race. The shells are tippy vessels with the lowest of freeboard and yet on any morning that a pleasure boat might make way through the cut, they will. Stability is gained by balance. The balance of the extended oars and attention to the details of catching, driving, feathering and recovery.These vessels rocket. A sailboat built for high performance sailing is similar. The form presented to the water when under sail will be thin and shell-like or as is sometimes stated racing-canoe like. That is a simlar shape presented by the Murrelet when heeled at ~ 17 degrees.

Murrelet doesn’t have oars for balance, instead she has water ballast tanks as far from the centerline as possible, which provides stability like extended oars would and maximum hull speed is reached with wind that is normal when heeled between 15 and 20 degrees. A sailboat that is sailed at an angle of heel greater than 25 degrees has too much sail up or needs more ballast.There is a physical law that limits maximum speed in displacement hull vessels. The law dictates that the smaller the length of the vessel at the water line, the slower the maximum possible speed. It has to do with the inability of a displacement hull vessel to climb its own bow wake. The Mac26x hull design is displacement like in the bow but is a planing hull further aft. Hence by moving crew aft and reducing heel to 10 to 15 degrees it is possible to break out of displacement mode and reach planing speeds.This is possible on reaching and down wind points of sail. Upwind, Murrelet is limited to hull speed.

In combination with another long used stability mechanism called water ballast DSS should be the future of yacht design.  Completion of the Sydney Hobart race in 2014 signaled the end of experiments in bulb fins. Prior to that race, which showcased Wild Oats against the most advanced canter, Comanchee, the IMOCA 60s had already started converting to DSS. The canting bulb keels, which do nothing for lateral resistance, are being fixed in the IMOCA 60s and the large wetted-surface area bulbs removed, so that foils for lateral resistance when sailing upwind at hull speed can also be removed. A review of comments below (to be authorized by site administrator) demonstrates that a DSS fitted Mac26x would be possible. A 27 foot DSS prototype was used to show DSS feasible. However, the Mac26x already has Dynamic Control. The following is from Section II of the Tasar Manual.

Dynamic Control; Learning to steer a planing hull

a) Steering for balance

The technique first learned by all sailors is to respond to heeling to leeward by luffing the boat into the wind and, conversely, to respond to heeling to windward by bearing away. This technique is correct, (provided that luffing or bearing away is done in a smooth, gentle manner) but it must be stressed that it should only be used when sailing to windward close-hauled. When a Tasar or any other light sailboat is sailing fast off the wind precisely the opposite technique must be used it must be “steered for balance’. The technique of steering for balance is exactly the same as driving a car at high speed (Fig.20)

If the car (boat) starts to roll over to the left, only by turning it to the left toward the direction of the roll will it be brought flat again. This is sometimes referred to as “steering the hull under the rig”. The beauty of this technique is that the faster the car (boat) moves the more responsive it becomes to this form of steering and, in the case of the Tasar, the steadier and easier to keep upright.

A number of principles are involved; Steering for balance is dynamic control and depends upon speed. At low speed it is in-effective. At high speed, its control becomes dominant. Conversely, if the reverse technique is applied at high speed, the result can be embarrassing.

A classic example is when a lull is suddenly encountered during a high speed reach and the boat heels to windward. The skipper who, at this moment, bears away from habit will capsize his boat to windward. And the skipper who steers for balance by luffing under the windward heeling rig, as the boat slows down, will enjoy perfect control.

To steer for balance, the boat must roll the proper way when turned. A Tasar sailing fast with its centerboard down or “half-up” will roll to the left when turned right as in Fig.20. This is exactly right for steering for balance. But if the centerboard is pulled all the way up, when it is turned right, it will roll right (like a speedboat) in which case, steering for balance won’t work. So when reaching or running really fast, never raise the centerboard above half-up.

b) The balance position

When broad reaching or running in any boat in strong winds, the mainsail should never be eased beyond the balance position. When the mainsail is sheeted closely, the boat will heel to leeward (Fig.2la)

As sheet or traveler is eased and the upper mainsail trims approximately at right angles to the center line, a position will be reached at which the boat does not tend to heel either way – this is the balance position (Fig.21b).

Broad reaching

If the mainsail is eased further, the top of the sail will blow forward of the mast (even if the boom is still at right angles to the center line) and the boat will heel strongly to windward (Fig.2lc)

The consequence of this behaviour is that when broad reaching or running in strong winds, normal handling technique must be modified for proper control. A description will make this clear. When a boat is close-hauled or beam reaching, a strong gust will heel it to leeward, and easing the mainsail eases the heeling force and helps bring the boat upright. But when broad reaching or running with an eased mainsail, any further easing of the mainsail can only result in the boat rolling forcefully to windward.

To sum up – when close-hauled or beam reaching in strong winds, the mainsail should be eased in a gust. But when broad reaching or running in strong winds, the mainsail should never be eased in a gust. Instead the balance position should be sought, the mainsail never eased beyond it, and the boat “steered for balance under the rig.” The stronger the wind and the faster the boat sails, the more certain will be this method of control.

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