Patents, underwater devices and the screws of Santa Maria del Fiore

The Renaissance artists/engineers already felt the problem of protecting their technological knowledge, inventions and "secrets" with what are now called patents. One example can be seen in the request made by Brunelleschi to the Florentine Signoria in 1421 to protect the invention of the "badalone", a boat designed by him to transport slabs of marble from the quarries at Carrara to Florence.
Around 1506, in the Codex Leicester (f. 15A-22v), Leonardo asked himself, «Why do I not write about my method for remaining under water?… I do not publish or divulge it due to the evil nature of men, who would use it for assassination at the bottom of the sea ….». This passage shows an ethical sense of secrecy that seems to contrast with the notes on a youthful folio in the Codex Atlanticus, where Leonardo shows himself primarily jealous of his secrets («Do not teach and you alone will excel»). Here he was in fact describing the way to sink enemy ships by surprise, with divers who would use Brunelleschi's screws, the same employed on the construction site of Santa Maria del Fiore («Bring one of the 3 iron screws from the works of Santa Liberata»). In this way Leonardo thought of managing to capture enemy commanders so as to collect a ransom, but with a written agreement stipulated to ensure the gain: «Take the commanders in your own way and secretly, with many bonds, put them ashore, but first make a pact through an instrument [a notarial deed], that half the reward will be yours, freely and without any exception».