Brown 1978 shows a horizontal blue–white–blue triband with a blue C in the white stripe. Rosanoski associates it with Pettersson’s company, approximately 1950–80. Later Mengwall funnel markings suggest that the flag did not pass to the successor.
Arne Elmer Pettersson acquired Dagö on 15 February 1950 and transferred her to Rederi A/b Castor that April. He operated the company through the following two decades. Its last listed vessel, Svanfjord, was sold in 1980 and renamed Sundex.
Sweden, Skärhamn; later Uddevalla.
Keep the explicit scope label independent; no alias or company identity is inferred.