Flexible flyers

Iceboats and scows can move faster because they have flexible mast, sail, hull, and runner plank that produce apparent wind while working in unison. Working here means bending and stretching that can push the boats to move in excess of 80 miles per hour.

Have you ever raced across a frozen lake, inches above hard black ice, at speeds in excess of 80 mph? What is it that makes an iceboat so fast? Part of it is the iceboat’s ability to generate apparent wind, but just as important is the interaction of the mast, sail, hull, and runner plank, which must work in unison for maximum speed and control. And by “work” I mean to bend and stretch, for on the world’s fastest sailboats, stiff is slow.

For years, soft-water sailors have been striving for the stiffest hulls and masts. But hard-water sailors know that you can make an iceboat too stiff. In the fastest soft-water boats – the A and E scows – we’ve implemented our iceboat philosophy and designed hulls and masts that have some flexibility. These scows have proven to be faster for the same reasons that flexibility is fast in iceboats.

Why Bend is Fast

It’s a common misconception that energy is lost when a boat bends. In fact, bend in an iceboat captures energy and enables the boat to accelerate out of a puff in a controlled manner. As a puff hits, the tendency for a stiff hull, mast, and runner plank is to cause an iceboat to “pop up in a hike,” or heel over quickly. Control is compromised, and you often have to spill power by easing the sail. But if the hull, mast, and runner plank all bend in unison, and in the right increments, the iceboat absorbs the sudden puff and quickly turns it into speed. Control is maintained and the boat remains on track.

Flexibility itself is not enough. These major components also need good “memory.” They must bend quickly as the puff hits and then recover to a normal position just as quickly. If the mast and runner plank don’t have good memory, they bend out to a maximum position and stay there after the initial shock of the wind gust hits. As a result, the boat takes longer to accelerate, will not accelerate to as high a speed, and will not point as high. Memory gives the iceboat “life.” When the mast and plank recover quickly from the initial shock of the puff, the acceleration is immediate and controlled.

Anatomy of an Iceboat

Depending on the iceboat class, the hull can be made of wood, fiberglass, or carbon fiber. Weight isn’t important, except in conditions when the ice is rough. Flexibility in the hull is important, especially as the wind increases. The hull must bend if the boat is to be forgiving and easy to sail.

The runner plank (which spans the two outboard runner blades) must also bend, but the range of flexibility needs to be larger. Runner planks are typically made of wood with multiple laminations and are customized to bend to a specific sailor’s weight. A typical plank is laminated with several inches of “crown,” or camber, and will deflect 6 to 10 inches when sailing. Heavier sailors use stiffer planks with more crown.

Iceboats have rotating wing masts. In the smaller iceboats, such as the DN, the masts are extremely “whippy.” As an iceboat accelerates, the apparent windspeed builds, the sail is trimmed harder, and the mast bends. This flattens the sail, which allows more boatspeed, which means more sheet trim, and so on. This trim cycle is repeated until the layman would swear the mast was about to snap. Much of that mast bend is sideways, but because the wing is rotated into the wind, side bend is a very effective way to flatten the sail.

As the boat accelerates, the apparent-wind angle also moves forward. If the sail didn’t get flatter, you wouldn’t be able to point. To give you an idea of the speed and apparent-wind angles that are generated, an iceboat runs downwind with the sail trimmed in tight in most conditions.

The mast must also react like the hull and runner plank, absorbing the puffs as they hit and turning them into speed. The fastest masts are those that can quickly bend an extreme amount and then recover immediately as the puff subsides. The bow and arrow is a good analogy. The memory of the bow is what gives the arrow its speed and acceleration. An iceboat mast is typically made of wood, fiberglass, or carbon fiber of multiple laminations, and must have the same memory.

The sail is the final piece of the puzzle. A fast sail should be draft forward and straight-leeched. It must be matched perfectly to the mast so that the sail completely flattens out when the mast bends. Full-length battens are used, and there are several sets (of varying stiffness) used in different wind conditions. While the rest of the sailing world moves to stiffer and less stretchy fibers in sailcloth, iceboaters have found good old Dacron is still the fastest. A Dacron sail is stretchy enough to allow the sail to twist open automatically as a puffs hit. This “flexibility” is yet another aid in the acceleration package.

By now, you should be dying for an iceboat ride. Here’s a taste of what it’s like to round the weather mark in a Skeeter: You’re on the layline approaching the mark in 20 knots of wind, doing about 70 mph, and starting to feel the apprehension. As your leeward runner reaches the mark, you push as hard as you can on the starboard foot-steering pedal. The windward runner lifts off the ice, slowly at first, increasing rapidly as you whip the boat onto the run, never easing the mainsail. Your body is forced into the back of the seat as the boat accelerates to 140 mph, creating G forces that no other sailing vessel could match. The adrenaline rush is unbelievable. You’ve just pulled off the most dangerous iceboat maneuver and are now speeding downwind within feet of several other iceboats, if not overlapped. Remember, this is a race, and you are only in control of your craft by the grace of all those magically flexible elements.

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