Wednesday, August 12, 2009

Form Follows Function: 3, Sailing Ships' Design

19th-Century British warship. wiki Click here to see full view.

Dutch Man O' War. wiki Click here to see full view.

Sailing ships are another class of objects that visually express their functions, often beautifully so. Few objects so clearly exhibit the functional purposes of individual elements as do these ships. The intricacies of full-rigged ships have been an undying source of fascination for centuries.

17-century merchantman. Dorset County Museum. wiki

A 17th-century warship. Vasa Museum, Stockholm.

The main functional bases of form spring from the capture of wind, sails; the need for balance, ballast; and the means of controlling direction and the amount of sail deployed at a given time.

Extensive descriptions of American sailing ships are available here.

All other things being equal, the more sail area, the more wind can be captured. The size of sails was limited by how they could be handled, so the vertical division of sails evolved into multiple tiers. The area exposed to the wind could be controlled by complete or partial gathering and unfurling. Access was provided by means of rope ladders and other rigging components. The process of managing the sails was essentially a push-pull relationship between the sails, masts and hull by means of ropes. The combination of these elements makes up the ship's rigging.

I asked a friend with a USCG captain's license, Lanny English, about the jibs, the triangular sails at the front of a ship. Along with defining apparent wind, he explained that these sails provide lift to the ship's prow, needed because the force gathered in the sails of the other masts tend to push the front of the ship down, as the height of the masts have the effect of levers. Lanny also pointed out that the action of wind and sails is analogous to lift on an airplane wing, with the "lift" effect of the void on the downwind side of the sail pulling while the direct wind force hitting the other side of the sail is pushing. A further explanation of the physics of sailing is here.

Click here to see full view. Here, the arrangement of masts, hull and stays clearly illustrates the structural system they comprise. This is a two-dimensional diagram, though, and a 3-d view would illustrate rigging that is perpindicular to the plane of this drawing. Article here.

Hull thickness had two main variables other than structure and water-tightness. These were simply whether the ship was expected to withstand shelling or not. A man o' war would tend to have a much thicker hull than, say, a whaler or freighter.

Hull configuration was largely determined by an inevitable tradeoff between stability and speed. For military use, though, a more complex array of factors came into play. A good artilcle describing the evolution of 19th-century battleships.


Rick McClain A very complete glossary of terms for sailing ships.

No comments:

Post a Comment