Recto: Designs for boats. Verso: A design for a paddle-boat, and the head of an old man in profile

This drawing studies the construction of boats of various sizes – the line of circles in the lowest study are the heads of a bank of rowers. The notes describe the mechanism of a boat propelled by paddle wheels, as drawn on the reverse of this sheet (beside the head of an old man) – a crank handle to turn a large toothed wheel, which is engaged with a smaller toothed wheel on the axle of a large paddle wheel, such that when the crank is turned the paddle wheel would spin quickly. Leonardo’s calculations promise a speed of 50 miles per hour, but he seems not to understand that while such gears would increase the speed of rotation of the paddle wheel, they would also require proportionally greater turning force (torque) in the crank to do so. Melzi's number 18. Text adapted from Leonardo da Vinci: A life in drawing, London, 2018