Join Date: Feb 2000
Location: Annapolis, Md
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Question? Swinging BOOM?
It sounds like you did an accidental jibe. A jibe is when the wind passes across the stern of the boat from one side to the other (as opposed to a tack in which the wind passes across the stern of the boat from one side to the other). In a tack, the boom swings with the comparatively slow speed that the boat is turning, but in a jibe, the boom swings with the usually much higher speed and force of the wind.
When you want to jibe it is important that you do so in a controlled manner. Intially this means bringing in the mainsail to the centerline of the boat before you make a slow turn putting the stern through the wind. Once the mainsail has crossed to the new leeward side, ease the mainsail back out before turning onto a reaching course.
In practice this is not all that hard taken a step at a time. To prevent accidental jibes while learning to sail, avoid going dead down wind until you feel comfortable with your boat handling and wind direction detection skills.