Here is something that might be of interest. This site
includes a newspaper article which describes how the "Unicorn" ship in the original strip was designed in the early 1940s.
In this article, Gérard Liger-Belair explains how he was one of Hergé's earliest collaborators and technical advisor. It includes a drawing of Tintin, Haddock and Calculus with a model of the "Unicorn", which appears to be dated 1945 and was dedicated by Hergé to Liger-Belair.
The site was made by Liger-Belair's grand-nephew Gilles Fallise who also made a model of the "Unicorn" the way Tintin finds it at the bottom of the sea in "Treasure".
According to the article, Liger-Belair became a friend of Hergé when they were both in the scouts. He had a passion for model building and opened a shop selling model sets. Hergé consulted him as a technical advisor for his stories and Liger-Belair designed the Stratonef, the plane in the "Jo, Zette and Jocko" adventures "Mr. Pump’s Legacy" and "Destination New York".
When Hergé came up with the plot for "Secret of the Unicorn", he asked Liger-Belair for a model which he could use for his illustrations. Liger-Belair went to the naval section at the Bibliothèque royale ("Royal Library") in Brussels and came across documentation about ships that served under the French Admiral Anne Hilarion de Costentin de Tourville at the time of Louis XIV. One of these ships was called the "Licorne" (French for "Unicorn"), which was sunk during the battle of La Hogue in 1692 during the Nine Year's War between Louis and practically the rest of Western Europe, including England.
(According to the French Wikipedia there was no ship called the "Licorne" at the battle of La Hogue and it is assumed that he was actually talking about the "Triomphant" ("Triumphant") which had a unicorn as a figurehead and was destroyed when the powder store exploded! - in battle, not by sabotage, the way François de Hadoque deals with the pirates.)
Liger-Belair designed the ship on tracing paper and created a simple model which Hergé could then use for his illustrations, seen from different angles. He later made a more detailed model which Hergé kept in his office long after he had completed the story.
Liger-Belair also claims that at the time he came up with the idea of "Tintin magazine" but Hergé rejected it, telling him he was an artist not a businessman. However Hergé did launch "Tintin magazine" after the war. Liger-Belair joined the staff as technical advisor, most notably by contributing to articles in which Haddock and Major Wings (the seaplane pilot in "Shooting Star") explained the history and technical details of ships, planes and balloons, which were later the basis for the "Voir et Savoir" Tintin-themed history books
. Another column he wrote featured Calculus instructing children how to make simple things to play with such as a tin can telephone
or answering questions on scientific matters. After three years of that, Liger-Belair quit in order to concentrate on his shop. He gradually lost touch with Hergé but later befriended Jean-Pierre Talbot who played Tintin in the 1960s live action movies "Golden Fleece"
and "Blue Oranges"