In addition to the Dutch Barge Dog, there is also the "Barkenspitz" as a synonym for the Keeshond.
A barge is an elongated, light ship with little draft, which is also known as a "lighter", "light ship" or "barge" (Hamburg). It can take over the cargo from larger ships and "light" them.
There are different forms of "lighter". They are all used in inland shipping and have one thing in common: they do not have their own drive. By the end of the 19th century, most barges were powered either by sails or by the only other means of propulsion available at the time: horsepower or manpower.
The barges sailed the rivers and canals that ran through the Netherlands and Belgium (from the 16th century to 1830 they were one and the same), the routes also passed through Germany and France.
In addition to large boats, there were also smaller ships called "Rijnaken". On these, too, the dogs had the task of jumping from the ship onto the shore in order to bark and chase away strangers. The records say that their primary purpose is to make noise, and their size should make them imposing and frightening. However, there is nothing about these dogs attacking or even biting.
River traffic was extremely widespread, in which, in addition to general crime, there were wars, riots, social and economic crises, etc. at different times.
The barge dog was used to guard these barges because of its robustness and size. Breeds were less of a concern then - there were only dog types and no official breeds - it was more important that they be vigilant and intimidating.
Book: Jan the Dutch Barge Dog by G.W. Barrington
Sources:
dogdiscoveries.com
www.k9uominiecani.com/
https://de.wikipedia.org/wiki/Lighter_(ship type)
www.europeanwaterways.com
1781–1795 Patriots vs Orangists on the Wayback Machine, Timeline Dutch History, Rijksmuseum, Keeshond, Historisches Museum Den Haag
https://www.todoperros.com
BI Lexicon Dog Breeds", 1st edition 1984, Michael Lissmann, page 214 ff.