A body carried half in the water and half in the air
How the relative speeds of wind and current set the speed of a half-submerged object
Leonardo analyses a body floating half-submerged, whose motion depends on how the air moving above compares with the water below. When air and water move at equal speed in the same direction the body reaches its first degree of quickness; if the air lags behind the water the body is slowed, the more so as the two speeds differ, while air faster than the water speeds it up. When equal air and water push in opposite directions, the body follows whichever medium it touches more. The folio is entirely text, without diagram.
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Speed of a half-submerged body under matching or differing flows
A body half in water and half in air moves at its first degree of quickness when air and water share one speed and direction. Air slower than the water slows the body in proportion to the difference, while air faster than the water quickens it.
When opposing air and water contend, contact decides the course
If air and water move against each other at equal velocity, the body follows the water if it touches the water more, and follows the air if it touches the air more.