I had my problems too. The name on the stern looks rather clear: MADRIGAL, CADIZ. Here the link to the photo on the NIMH website: https://nimh-beeldbank.defensie.nl/beeldbank/indeling/detail?q_searchfield=2000-1225-017. The photo can be enlarged. What is your opinion? There was a ship named CASTILLO MADRIGAL which was in The Netherlands in August 1949, however at Delfzijl.
The funnel with the red rectangle corresponds indeed with the company Empresa Nacional Elcano, see http://www.buques.org/Navieras/Elcano/Elcano-1_I.htm. They were also the owners of the Castillo Madrigal, but that was clearly another ship.