Broach (nautical)

A broach can result from one of two causes, wind action or wave action, or a combination of the two. A sailing vessel broaches when a wind gust heels (leans) it over—causing the rudder to be unable to control the direction of the vessel—and suddenly changes course towards the wind. Any vessel may broach if it is traveling downwind in large waves at a speed that is close to that of the waves—this can cause the rudder to become surrounded by water moving at close to the same speed as the vessel, because of the forward rotation of the upper parts of the waves, and thereby cause loss of control. Both situations cause the rudder to become ineffective, either from approaching horizontal when the vessel heels in the wind or by being surrounded by water moving at a low relative velocity.


RS K6 Keelboat broaching, caused by wind action.

Caused by wind action

Broaching caused by wind action may occur when a vessel is sailing away from the wind and its sails are suddenly overpowered by a gust of wind, causing it to heel excessively. The heeling causes the rudder to move from a vertical orientation towards a horizontal one and thus become less able to control the direction of the vessel. With loss of directional control, the vessel turns into the wind.[1] In the process, the vessel may heel close to horizontal and possibly capsize.[2] Such loss of control may be preceded by oscillations of the vessel's mast and course, as the person steering attempts to maintain control.[1]

Caused by wave action

Any vessel that is traveling in the same direction and close to the same speed as large waves (relative to the vessel) risks losing directional control when the stern is lifted in the water by an overtaking wave. Near the crest of a large wave, the orbital motion of the upper part of the wave is in the same direction as the vessel's course and can be close to the same speed as the vessel. When the orbital motion of the wave minimizes the velocity of the rudder through the surrounding water, it loses effectiveness and compromises steering. The vessel is likely to swing across the waves, roll to one side, and perhaps capsize.[3] Wave action may contribute to a broach initiated by wind gusts.[1]

See also

References
  1. Colgate, Steve (1979). Anne Madden (ed.). Oscillation and Rolling. More Sail Trim. Sail Books Inc. and Adlards Cole. p. 138.
  2. Bruce, Peter (2016). Heavy Weather Sailing (7th ed.). Bloomsbury. p. 248. ISBN 9781472928207. Retrieved 21 June 2017.CS1 maint: ref=harv (link)
  3. Rawson, K.J.; Tupper, E.C. (1976). Basic Ship Theory. 2. Elsevier Science. p. 562. ISBN 9780080523385.

Bibliography
  • Sailing yacht broaching
  • Tank test of power vessel broaching
  • Training material for power vessels


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