Image from Flag chart of house flags of Dutch shipping companies, attached
to the magazine "De Blauwe Wimpel", April 1956.
Jarig Bakker, 9 Aug 2003
N.V. Houtvaart. Formed 1910 the flag appears to have originally had
the diamond throughout with a change in the 1950s to the version shown.
Going by Brown 1978 there was another alteration with the addition of small
outer extensions to the vertical lines of the "H".
Neale Rosanoski, 25 Sep 2003
original Houtvaart houseflag
by Jarig Bakker, 5 Oct 2003
Image according to the description above.
Jarig Bakker, 5 Oct 2003