On the Motion of Ships; Water Wearing Away Its Banks
Broad-bowed hulls shaped like fish and birds, and falling water eroding riverbanks
Headed "On the motion of ships," the page compares three hull forms, sketched top right beside profiles of fish, and argues that of three vessels of equal size driven by equal force the one presenting its widest part forward moves fastest, like birds and mullet. A second section, on the wearing that water makes in its falls, uses lettered diagrams to show how a cascade strikes and consumes the base of a bank until, its support gone, the bank collapses. A final note explains that falling water deepens the bed where it strikes.
On this page
Why a broad-bowed ship moves fastest
Of three ships of equal breadth, length and depth driven by equal powers, the one that sends its widest part in front is the fastest, resembling the shape of birds and of mullet fish. It opens much water at its sides and front, whose revolutions then press the ship from the rear two thirds; the hull d c does the opposite, and d f is middling.
Reflected whirling motions gnaw at the bank
Where water falls from height a c to n it strikes and consumes the struck place; m n c is the middle of the percussion, where the reflected motions n m o and n c b divide. These whirling reflected motions rub and consume the bank on every side, so that, its supports gone, it ruins where its stay fails.
A cascade deepens the bed where it strikes
Water falling from a b onto m n goes on deepening the bed from which it falls, down to the lowness of the place where it strikes, from a b to c d. The repeated fall is shown eroding both bank and bed.