For rhyme the rudder is of verses, With which like ships they steer their courses.

-Butler, Samuel
  Hudibras, pt.1, canto1, l.457^8.

By viewing nature, nature's handmaid art, Makes mighty things from small beginnings grow: Thus fishes first to shipping did impart, Their tail the rudder, and their head the prow.

-Dryden,John
  Annus Mirabilis, stanza155.

Perspective is the bridle and rudder of painting.

-Leonardo daVinci
Quoted in Irma  A Richter (ed) Selections from the Notebooks of Leonardo da Vinci (1977).