More on Airships

This is a diagram of an airship executing a "cross," that is, a turn that moves across the direction of the wind. The short black lines are the four sails: a spritz'l afore, a mizzen astern, and two lateral mainsails, designated as leeward and windward or as starboard and larboard (port). In the diagrams below the larboard sail begins as the windward sail, but as the turn concludes it becomes the leeward sail.

Other important terms are open (said of a sail at a narrow angle to the wind) and closed (said of a sail approaching or at a right angle to the wind). An open sail produces more off-wind (away from the direction of the wind) force than a closed sail, although one must keep in mind that the mizzen sail, being the stern, when it has excess off-wind force, it produces an on-wind turn (toward the direction of the wind) in the vessel. A cross, incidentally, begins as an on-wind turn, and continues into an off-wind turn.

The red arrows indicate directions of force from each of the sails and for the turning of the whole vessel. The black arrows are movements of the sails, and the blue arrow in the lower left of each figure is the direction of the wind.

	Fig. 1 Sails balanced, the ship moves straight ahead. The hub shouts "Ready to cross!" Mastmen spring to the mainsails.
	Fig. 2 The hub shouts "Cross ho!" and the helmsman opens the mizzen, beginning an on-wind turn.
	Fig. 3 As the turn continues, the mastmen haul the windward sail and ease the leeward sail, maintaining trim to the turning ship. The spritz'l is opened to the wind by the turning ship, so the helmsman closes the mizzen to prevent the turn from accelerating.
	Fig. 4 As the ship comes to its new heading, the hub shouts, "Stay the course!" The mastmen secure the mainsails, and the helmsman opens the mizzen further to arrest the turn.
	Fig. 5 The mastmen now spring to the spritz'l, and bring it into trim, and the helmsman trims the mizzen. The ship is on its new course. Sailors make fine adjustments to the set of all four sails, and then the mastmen have a break.

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