J. Zeeman, De Nederlandse Stoelklok, Assen 1969, pp.197-206
Dr. J.L. Sellink, Dutch Antique Domestic Clocks, Leiden, 1973, pp.241-243
Catalogue Zaans Uurwerk Museum, Klokken, 1976, p.28
The 'schippertje' (barge clock) may be considered a miniature version of the conventional 'Frisian stoelklok'. The clock's name is said to derive from its use on rolling inland barges. The special feature on 'schippertjes' is the integral back-swinging pendulum, rigidly connected to the verge. This arrangement prevents the pendulum bob from making contact with the movement or bracket -- and therefore stop swinging -- when the barge rolls.
Dating 'schippertjes' is not without its difficulties. Zeeman describes three examples of 'stoelschippertjes' which are generally considered to be 18th Century examples, all with integral back-swinging pendulums. Zeeman refers to an academic discussion about clocks with the pendulum swinging to the side which some consider to be the only true 'staartschippertjes'. One feature which is important in dating these types of clocks as being 18th Century examples is the size of the movement. Known 18th Century clocks all have small movements varying in size from 7.5 cm. to 9 cm. in height. The present clock, with a 7 cm. high movement, may therefore be considered as a very small and rare example of an 18th Century 'stoelschippertje'.