A narrowboat or narrow boat is a boat of a distinctive design, made to fit the narrow canals of the united kingdom. a narrowboat must be under 7 feet (2.13 m) wide (most modern boats are usually produced to a maximum of 6 feet 10 inches (2.08 m) wide).. Canal holiday advice cheaper thank you think how much will it cost? prices are highest during the summer months (june, july & august) when a fully catered and organised hotel boat week for one person will cost about