The English-speaking world clearly distinguishes the ship designers into naval architects and marine engineers, who are normally, respectively, the designers of the hull and of the propulsion plant. These are indeed two very different disciplines which, although interfaced, have differently influenced the evolution of the ocean liner.

Italy has a long tradition of naval architecture which, in modern times, was emphasised by the opening of the first test tank in Continental Europe for the towing of scale hull forms in La Spezia; the shape and appearance of the top of the ship was, unlike that of the hull, mainly influenced by the type of service, of routes and by the demands for transport of passengers, freight or both.

The hull shape was obviously affected by the type of propulsion used, whether paddle wheels or propeller; the first deep sea-going screw steamer, the Civetta, had been successfully tested by her inventor Josef Ressel (1793-1857) in 1829 in the Gulf of Trieste but it would take many more years before the paddle wheels were definitively supplanted.

The proverbial prudence of the Ligurian people (that is, the inhabitants of Genoa and the neighbouring area) would lead in the middle years of the XIX century to the development of the first hybrid sailing/steam ship, known as "screw clipper", i.e. a fast sailing ship fully fledged with masts and sails full kit but also with a steam engine and its propeller. In those days the steam engine was not reliable enough to convince shipowners to adopt it, its operating costs were high due to the huge consumption of costly coal; it was still a rooted conviction that, especially for long journeys, the steamer could not compete with the sailing ship, whose “free-fuel” compensated the longer duration of the trip. The screw clipper would therefore constitute the first shy step towards the embracing of modern technology at sea.

Giovanni Battista Lavarello (1824-1881), a native of Recco, near Genoa, was the pioneer in commissioning screw clippers. After gaining his first experience at sea as captain and owner of sailing ships on the routes to Latin America and the Black Sea, Lavarello began a regular passenger and freight service between Genoa and the ports of Rio de la Plata with screw clippers. The first to enter service was the Buenos Aires, built by the shipyard of G.B. Cadenaccio at Sestri Ponente (now Genoa Sestri); she sailed from Genoa on her maiden voyage on the 4th January 1864, arriving at Rio de la Plata after 64 days.

The design and construction procedures for iron-and steel-hulled ships remained basically unchanged from the first buildings to the outbreak of the Second World War; the revolution was to come with the advent of computer-assisted design and prefabrication. The evolution of iron and steel building techniques during the first fifty years was related essentially to the introduction of upgraded equipment in the shipyard, from the systems of transportation to increasingly powerful and sophisticated machine tools, which gradually replaced the use of human labour in several fields.

In the beginning a slipway was built on the shore and the plates were carried to its side, carted there by beasts of burden. Once in place with large shears and perforated at the edges, they were riveted together. The flat lay-out of the plates was achieved by means of scale wooden models of half-hulls on which the strakes were drawn; the scale dimensions and shape of each plate where then transferred in full scale to the floor of the tracing room mould loft (on a sort of gigantic sheet of graph paper) using large battens and leads.

Riveting was used to join the plates together, rather than welding, which made its first timid appearance in the shipyards in the early 'Twenties before becoming widespread after the World War II. The millions of metal pins were originally hot-riveted by riveters, who were extremely important skilled workers in the organisation of the yard and were represented by their own unions. Riveters were assisted by two apprentices; one used to take red-hot rivet from the brazier with a pair of tongues and pass it to the other (the receiver) on the slipway frame, who would take it and insert it into the paired holes while another pair of riveters inside the hull took it in turns to hammer it until the head was perfectly round and flush.

Aluminium alloys (for the construction of all or part of the upperworks) which provide the same strength but weigh one third of steel, would lead to a further revolution soon after the Second World War, also affecting the appearance of the ship; with the same robustness, they allow weight savings of over 60% compared to steel, and led to a further revolution immediately after the war, also in the appearance of ships.

In 1963 prefabrication was succesfully tested in Monfalcone - for the first time on large passenger ships launched in Italy - to build the Lloyd Triestino twins Galileo Galilei and Guglielmo Marconi. This method basically involved the use of prefabricated hull sections made in the factory and assembled later on the slipway. The advantages in terms of quality as well as saving of time and cost – comparable to those of an assembly line – were enormous. Nowadays, prefabrication is optimised in shipyards everywhere, with the blocks positioned in the building graving dock when they already contain the plants, technical systems and most of the fittings, for example the cabins.