mainsail

1.bend a mainsail onto the boom.

把帆系在帆杆

2.reefing the mainsail in strong winds.

在强风中收缩帆。

3.Jibe: To shift the mainsail from one side to the other when sailing with the wind behind; also "gybe".

转帆：顺风行驶时将帆从船一侧转到另一侧。