Harrock n roll:
Hmmmm, not sure the Captain is that much bigger than the Thom(p)sons, nor that Calculus is as tall as them.
I knew I'd seen a model sheet for the Studios Hergé which came up for auction, in which Hergé depicts the characters side-by-side, to show their relative heights, which are ruled off so that comparison can be made.
Having found a picture of it, and with some margin of error due to the resolution of the available picture, the following proportions can be derived, if not the actual heights, as there isn't a scale on the diagram.
If Tintin is taken as 100%, then Calculus is 103% of Tintin's height, the Detectives are 113% of Tintin's height, and the Captain is 119% of Tintin's height. Snowy is 40% of Tintin's height.
If, as Hergé maintained, Tintin is 160cm, the following heights can be calculated, provided that my arithmetic is up to it, and E&OE:
The Detectives: 180cm
Captain Haddock: 190cm
Using Ville81's estimate of 165cm, the following would be the heights.
The Detectives: 186cm
Captain Haddock: 196cm
Hopefully a clearer, better resolution version of the sheet will be found to allow a refinement of these heights, but I think that these proportions are something to build on!