In September 1857 he returned to Barcelona, where he organized the first commercial society in Spain dedicated to submarine navigation, Monturiol, Font, Altadill y Cia.

He performed some hasty repairs on the damaged portholes, exterior hull, and ballast tanks, and limited his diving depth to 20 metres (66 ft).

Monturiol had originally wanted to build his pressure hull out of metal in the interests of strength but he and his financial backers lacked sufficient funds, so he instead settled for wood, with which he was familiar since his father was a cooper.

Several thick glass ports were installed on the sides, top, and bow of the Ictíneo; these were semi-conical in shape so that water pressure would tend to force them more firmly into their seats, helping in avoiding leaks.

Monturiol also included a large weight mounted inside the submarine on a longitudinal metal track, which could be moved back and forth to counteract shifts in the vessel's centre of gravity.

For interior illumination he used a candle, which had the advantage of turning red when oxygen was beginning to run low, which would alert the crew.