The powerful hull at right, surging ahead like a surfboard, is one of an exciting new type of sailing craft called planing boats. Capable of moving at triple the speed of conventional boats, they have advanced the art of sailing into a truly new dimension. Until planing boats were developed (SI, April 28, 1958), the speed of a sailboat was limited by the length of its waterline. Every boat moving through the water made a bow wave and a stern wave (top diagram, right). And once the boat reached a given speed, it could not go any faster, because to do so it would have to climb up its bow wave. Because of weight and the shape of the bottom, the conventional displacement hull could not rise out of its own wave trap. The planing boat, however, is designed to escape the trap. Light in weight, with powerful sails and a flat stern, it behaves like a displacement boat in light winds (center diagram). But when a puff hits, the force of the wind, counterbalanced by the weight of the crew, pushes the boat onto the bow wave. Then the flat bottom, instead of mushing down in the water, forces the light hull toward the surface until it pops out of the trap and skims along (lower diagram) on the crest of its own bow wave. The key man in the development of planing in the U.S. is George O'Day of Marblehead. As a salesman he has distributed more than 900 planing hulls. As a racing skipper he has won the Men's North American championship in a Thistle-class planing boat. Last summer, using the skills he refined in planing, he won an Olympic gold medal in the displacement-type 5.5-meter boats at Naples. At right and on the following pages, O'Day, with the help of his Olympic crewman, Dave Smith, demonstrates these skills both for planing sailors who want to master their high art and for sailors of conventional hulls who can use some of these same advanced techniques to make their own boats go faster.


The 5-0-5 carries all the equipment and has the design characteristics commonly found in planing boats. She has a fiat stern to help her get onto a plane. She weighs 280 pounds (compared to 425 for a comparable nonplaning class, the Snipe) and has 150 square feet of sail in her mainsail and jib (a Snipe has 115). Because of her light weight and her big sails, she needs special gear to keep her upright. The most potent piece of equipment is the trapeze (1). This consists of a wire attached to the upper part of the mast, with a wide belt that snaps on at the lower end. In heavy winds the crewman clips the belt to the wire and hangs out over the windward side (above). There he can exert three times the leverage of a man perched on the windward rail. The less spectacular hiking straps (2) are canvas belts under which the legs can be hooked to allow both the skipper and the crew to lean (hike) over the water from the hips up. The extension tiller (3) lets the skipper control the boat while he is hiking. The boom vang (4) is a short wire that holds the mainsail in its best shape. The trapdoor bailers (5) are a pair of hinged flaps held by elastic cord (upper diagram, right) that can be released (lower diagram) to drain the fast-moving hull if she ships water.

1 Ready to plane, O'Day and Smith sit on rail. Wind is broadside. Smith holds jib sheet; O'Day holds main-sheet and extension tiller, while he watches for dark patch on water that means strong puff of wind is coming.

2 Wind hits and boat accelerates. Both men move outboard, bringing their ankles up against the hiking straps and leaning out quickly. At same time O'Day slacks mainsheet about a foot, ready to pull it in fast to help pump the boat onto a plane.

3 Breaking onto plane, O'Day pulls sail in quickly, and both men hike far outboard. Boat now surges ahead on top of its own bow wave, leaving typical flat wake as 5-0-5 jumps speed from 5 knots to 10 or more.


Trapeze is used only when wind is blowing so hard that hiking with straps, as O'Day and Smith are doing in gentle gusts above, will not keep hull flat. Crewman, however, wears wide foam-padded belt continuously, whether it is attached to wire or not. The wire—actually two wires, one on each side of mast—is held secure at lower end by elastic cord. Getting out over water is fast, tricky work. Here O'Day momentarily relinquishes tiller to show proper procedure. First, with belt hooked onto wire, O'Day, jib sheet and wire in right hand, slides back (A) to brace left leg stiffly against trapeze block. Then (B) O'Day pulls jib sheet taut and pushes off with right leg. Next he swings over water (C), keeping left leg stiff, right leg relaxed to act as shock absorber. Coming back in (D), he slips foot under hiking strap before removing belt wire.


Getting a boat to plane is fun in any circumstances, but in a race it is absolutely essential, for the first boat up will double the speed of its rivals. Therefore the skipper and his crew must watch the wind and learn to feel when the boat is going almost fast enough. In a 5-0-5 this will be at about 6 knots and requires a wind of at least 10 knots. The instant they feel conditions are right, the men must lean far out, pump the sails and try to bounce the boat out of the trough created by its bow and stern waves and get it up onto a plane.

The most important factor in planing, as in all sailing, is the direction and strength of the wind. A planing boat reacts most efficiently to wind coming in from slightly forward of broadside. Therefore, in the sequence at left and below, O'Day and Smith bring the 5-0-5 broadside to the wind. As a puff hits, they do a precisely timed, simultaneous backward and outward hike to keep the boat on its feet so its broad stern can help lift it up. On a gusty day, when the wind first drops below planing strength and then rises again quickly, the 5-0-5 will go on and off plane repeatedly. The skipper and crew then have to move in and out constantly to keep the hull flat on the water. If they move out too soon, the boat will tip awkwardly to windward, spilling wind from the sails and losing way. And if they move out too late, the boat will miss the chance to get up; or at worst it will flip over, leaving all hands paddling in the water.


Once the boat is on a plane, keeping it there calls for finesse and judgment, especially in maintaining the best, most powerful angle with the wind. As the 5-0-5 accelerates, the direction of the wind experienced on board shifts toward the bow (small arrows in diagram below left), even though the direction of the true wind over the water (heavy arrow below) remains the same. This new and varying wind direction is called the apparent wind and is a combination of the true wind and the air which naturally flows back as the boat moves" rapidly forward. If the boat is not handled properly, the apparent wind will eventually swing so far toward the bow that the boat will slow down and drop off its plane. Therefore, as the boat accelerates, O'Day keeps the apparent wind at the correct angle, by driving off (veering downwind). In the diagram, the second and third hulls from the top show how O'Day keeps the apparent wind coming over the side of the hull at a constant angle. As the boat speeds up, both men have to hike out farther. For not only does the apparent wind change direction, but the increasing speed of the boat itself adds to the power of the apparent wind. When the wind drops off, however, O'Day must sense the change immediately and swing the boat back to the original course. The snakelike path that results from driving off and coming back is typical of a well-skippered, planing hull. The enormous advantage of keeping the boat driving at top speed more than makes up for the curving passage through the water.

1 In steady wind, the boat planes perfectly, kept flat by hiking of O'Day and Smith.

2 In rising wind, O'Day drives (veers) off and slacks main. Both hike out farther.

3 Under control, O'Day pumps main to add speed as he continues to drive hull off.

Apparent wind shifts forward and then back, forcing boat to drive off and then return to its original course.



O'Day shows the techniques of planing downwind: how to ride the waves and handle a spinnaker.