@joansmor More correctly described as 'narrow boats', the standard being 7ft wide by 70ft long to fit the narrow canals and locks which were largely dug by hand so made no wider than necessary. More information here: https://www.waterways.org.uk/blog/evolution_the_narrow_boat
The French 'péniche' is a very different animal: https://en.wikipedia.org/wiki/Péniche_(barge)