Brunel switched the Great Britain to a screw propeller mid-build

In 1839 the Great Western Steamship Company began building the Great Britain, an iron ship larger than anything afloat, with paddle wheels planned for propulsion. That year Francis Pettit Smith's Archimedes became the first successful screw-propelled steamship.

When the Archimedes reached Bristol in May 1840, Brunel paused the Great Britain's engine work and spent three months experimenting with screw forms aboard the borrowed vessel. On 1 October 1840 he read a detailed report to the board, and the directors voted to adopt the screw.

The screw sat low in the water, was less vulnerable to damage and freed the hull sides for cargo and passengers. The Great Britain launched in 1843 as the world's largest ship — and the first iron-hulled, screw propeller-driven, steam-powered ocean liner.

Test a rival's screw on their ship first

The screw was less exposed to damage than paddles

It freed hull space for cargo and passengers

Three months of trials produced evidence, not opinion

Borrowing the Archimedes kept the cost of testing low

Before committing an irreversible design, borrow someone else's platform for the decisive experiments — evidence from a trial beats argument in a boardroom.

The Great Britain carried passengers across the Atlantic, then emigrants to Australia, and proved the combination of iron hull and screw propulsion that every later ocean liner followed; her surviving hull is now preserved in Bristol.