Model of the ship Real Carlos, originally built as the Santísima Trinidad (104-gun).

The model reproduces a fully-rigged, 3-decker ship, with standing rigging and running rigging—typical of a mid-18th century ship. At the time, the mizzen masts had not yet been introduced and the lateen yard had not been replaced by a gaff sail with a boom. The model is equipped with guns and the hull runs into a rounded stern, leading to corridors and ending in a horseshoe shape. It has an English-style taffrail with 3 arches, which has high-relief carvings and a medallion engraved with a bust of Charles III of Spain. The range of colors in the model allows us to see how ships were painted at that time.

The model was built at La Carraca between 1766 and 1767, based on ship plan numbered PB-197, held at the Naval Museum. This plan relates to a 114-gun ship drawn by Ignacio Mullan, and evokes its British origins. It was given the name Real Carlos by its designer, who presented it to the king. The type of ship depicted in this model was later reproduced in Havana with the building of the Santísima Trinidad. This ship resembled its contemporary, the Royal George (1756–82), a 100-gun ship launched from Woolwich which was built in accordance with the 1745 British Establishment for shipbuilding.

On August 14, 1767 an agreement was signed between Quartermaster Conde de Macuriges and Flag Officer Juan Antonio de la Colina in which it was agreed that a 3-decker ship would be built at Havana’s shipyard, when the 80-gun San Luis was launched. However, these plans were disrupted by the arrival of the Irish-born Mullan, whose project to build a 112-gun ship was given precedence. Those involved were so impatient that, without waiting for authorization in the form of a Royal Order, they began acquiring the timber and by October had already laid down the keel in the slipway previously occupied by the San Luis. However, Mateo Mullan died on November 25 of “black vomit” (yellow fever), much to the concern of the naval authorities on the island. Mullan had only drafted the ship’s main floor at the stern, the keel bolted onto keel blocks, the carved stem and the sternpost. In view of the situation, on November 27 (2 days after Mullan’s death) the Count of Macuriges took the decision to put Ignacio Mullan in charge of the plan designs, while Pedro de Acosta would take charge of fortifying the ship in line with Spanish standards, and of the overall supervision of the work. This situation, as well as the unusual mismatch in the tasks assigned to each shipbuilder (although Acosta died soon after), may explain the misfortunes that the ship suffered throughout its long history. The ship was named Santísima Trinidad by a Royal Order issued on March 12, 1768.