A sailboat
broaches when its
headingIn navigation, a course is the intended path of a vehicle over the surface of the Earth. The course is the intended path of a vehicle of a line drawn on a chart representing the intended path. It is expressed as the angle measured from an object clockwise from 0° through 360° to the line. The...
suddenly changes towards the wind due to
windWind is the flow of air or other gases that compose an atmosphere . On Earth, wind consists of the bulk movement of air...
/
sailA sail is any type of surface intended to generate thrust by being placed in a wind—in essence a vertically-oriented wing. Sails are used in sailing.-History of sails:...
interactions for which hull hydrodynamic reactions cannot compensate. This happens when the aerodynamic force on the rig greatly exceeds the hydrodynamic force on the hull, usually due to a sudden increase in wind strength. In small boats and dinghies, broaching often leads to
capsizeCapsizing refers to when a boat or ship is tipped over until disabled. The act of reversing a capsized vessel is called righting.If a capsized vessel has sufficient flotation to prevent sinking, it may recover on its own if the stability is such that it is not stable inverted...
(see
Death rollIn a keel boat, a death roll is the act of broaching to windward, putting the spinnaker pole into the water and causing a crash-gybe of the boom and mainsail, which sweep across the deck and plunge down into the water. The Death Roll often results in destruction of the spinnaker pole and sometimes...
). In larger boats broaching can lay the mast horizontal, putting both rig and crew at risk.
A sailboat
broaches when its
headingIn navigation, a course is the intended path of a vehicle over the surface of the Earth. The course is the intended path of a vehicle of a line drawn on a chart representing the intended path. It is expressed as the angle measured from an object clockwise from 0° through 360° to the line. The...
suddenly changes towards the wind due to
windWind is the flow of air or other gases that compose an atmosphere . On Earth, wind consists of the bulk movement of air...
/
sailA sail is any type of surface intended to generate thrust by being placed in a wind—in essence a vertically-oriented wing. Sails are used in sailing.-History of sails:...
interactions for which hull hydrodynamic reactions cannot compensate. This happens when the aerodynamic force on the rig greatly exceeds the hydrodynamic force on the hull, usually due to a sudden increase in wind strength. In small boats and dinghies, broaching often leads to
capsizeCapsizing refers to when a boat or ship is tipped over until disabled. The act of reversing a capsized vessel is called righting.If a capsized vessel has sufficient flotation to prevent sinking, it may recover on its own if the stability is such that it is not stable inverted...
(see
Death rollIn a keel boat, a death roll is the act of broaching to windward, putting the spinnaker pole into the water and causing a crash-gybe of the boom and mainsail, which sweep across the deck and plunge down into the water. The Death Roll often results in destruction of the spinnaker pole and sometimes...
). In larger boats broaching can lay the mast horizontal, putting both rig and crew at risk. It can be particularly dangerous when racing other boats at close quarters.
Sailing in variable, gusty winds is a common cause of broaching when sailing on a close reach and in strong gusty winds on a broad reach. When sailing on a
broad reachPoints of sail describes a sailing boat's course in relation to the wind direction.First, there is a distinction between the port tack and the starboard tack. If the wind is coming from anywhere on the port side, the boat is on port tack. Likewise if the wind is coming from the starboard side,...
, the helmsman must be careful to make sure that the wind is not allowed to cross the stern. If this happens, then the sails may fill from the
leewardWindward is the direction from which the wind is blowing at the time in question. The side of a ship that is towards the windward is the weather side. If the vessel is heeling under the pressure of the wind, this will be the "higher side"....
side, resulting in a sudden reversal of the direction of thrust as the sail moves from one side of the boat to the other. This is called a
gybeGybe may refer to:*Gybe, an alternative spelling of jibe, a sailing maneuver*To deride or tease with taunting words, also spelt "gibe" or "jibe" and done with a Sneer.*Godspeed You! Black Emperor, a Canadian post-rock band, commonly abbreviated to GYBE...
, and it can be a dangerous maneuver even when performed under controlled circumstances. When it happens unexpectedly, the
boomIn sailing, a boom is a spar , along the foot of a fore and aft rigged sail, that greatly improves control of the angle and shape of the sail. The primary action of the boom is to keep the foot of the sail flatter when the sail angle is away from the centerline of the boat. The boom also serves...
may live up to its name, as it crosses the boat under full load and may sweep unwary crew members overboard, unless a
preventerA preventer, or jibe-guard, is a mechanical device on a sailing vessel which limits the boom's ability to swing dangerously across the boat during an accidental jibe.The uncontrolled jibe is feared by all sensible yachtsmen...
is rigged on the boom.
One of the less obvious causes of broaching is an
oscillationOscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power...
developed when
runningPoints of sail describes a sailing boat's course in relation to the wind direction.First, there is a distinction between the port tack and the starboard tack. If the wind is coming from anywhere on the port side, the boat is on port tack. Likewise if the wind is coming from the starboard side,...
downwind. When running dead downwind, the sails are set with an angle of attack of nearly 90 degrees to the wind. The high angle of attack causes turbulent bubbles to form on the leeward side of the sail, and when there is insufficient attached flow to keep these bubbles attached to the sail, they separate. The sudden separation of a turbulent bubble drops the lift of the sail to nearly nothing, which causes the boat to rock slightly. At angles of attack near 90 degrees, lift can generate on the leech, or trailing edge of the sail. As the boat rocks due to separation of turbulent bubbles, a constructive interference is formed, as bubbles begin to shed from alternating sides of the sail. Once started, the oscillation builds quickly, especially in modern ultra-light displacement centerboard boats, which lack the damping effects of a large
keelIn boats and ships, keel can refer to either of two parts: a structural element, or a hydrodynamic element. These parts overlap. As the laying down of the keel is the initial step in construction of a ship, the construction is dated from this event, with only the ship's launching considered more...
. Once this oscillation reaches a certain point, the extreme change in heel angle will cause the boat to broach.
SpinnakerA spinnaker is a special type of sail that is designed specifically for sailing off the wind from a reaching course to a downwind, i.e. with the wind 90°–180° off the bow. The spinnaker fills with wind and balloons out in front of the boat when it is deployed, called flying. It is constructed of...
s generate lift from the top, rather than the side, and thus they are less prone to this form of broaching than other modern sail types.
Square rigSquare rig is a generic type of sail and rigging arrangement in which the primary driving sails are carried on horizontal spars which are perpendicular, or , to the keel of the vessel and to the masts. These spars are called yards and their tips, beyond the last stay, are called the yardarms...
ged vessels also generate lift from the tops of their sails, which in fact, combined with the large keels they traditionally use, makes them immune to this type of broaching.
Another cause of broaching is encountered in heavy seas and high winds. If the bow of the yacht is not kept pointed into the waves, then the waves will push the bow aside, turning the boat side-on to the waves. Once side-on to the waves, the waves will roll the yacht side to side violently, causing severe discomfort to the crew, the yacht may broach and may even capsize. Since a sailing ship cannot steer unless the sails are providing forward motion, and since heavy seas are most often from the same direction as the wind, a
sea anchorA sea anchor, used to stabilize a boat in heavy weather, anchors not to the sea floor but to the water itself, as a kind of brake. Sea anchors are known by a number of names, such as drift anchor, drift sock, para-anchor, and boat brakes...
may be used at the bow in extreme weather to keep the bow pointed into the wind and waves.