I've been delving into the University of Canterbury's art collection recently, as it has been made available on the University's web site, and was stoked to come across the two Petrus van der Velden drawings below.
Both drawings are preparatory studies for one of Christchurch Art Gallery's most treasured paintings by van der Velden, The Leuvehaven, Rotterdam (1867). The top drawing of shipping masts relates directly to the ship on the left of the painting while the bottom drawing is a study for the row of buildings also seen on the left hand side.
Van der Velden was a demon with charcoal and pencil. A highly-skilled draughtsman, he placed just as much importance on his drawings as he did on his paintings and his skill is particularly evident with the accuracy of the rigging shown in the drawing above.
The University of Canterbury's collection can be viewed online here and is well worth checking out.