The official 1888 canal returns give 61 feet as the maximum length for locks on the L&LC. Dowley Gap had the shortest chamber, at 64 feet 4 inches, probably measured between the quoins, where lock gates pivot against the lock wall, so not that much use in giving a true usable length. Although 61 feet is still often quoted, an 1898 specification for a typical boat gives a length of 61 feet 6 inches measured over the stem and stern posts, and the iron and steel boats sometimes quote 62 feet 6 inches, though this probably included the rudder. It is really impossible to be definitive to 6 inches, and we would always advise 61 feet as a guaranteed length, though it is possible for a longer narrow boat to use the locks diagonally.
However, when thinking of building a boat, always remember the Calder & Hebble Navigation, whose locks in 1888 were quoted at 57 feet 6 inches long with a width of 14 feet 1 inch, making them smaller than those on the L&LC. Elland Low was quoted as having the shortest length between quoins, at 60 feet 7 inches.
When it comes to length on canals, there is only one way to tell and that is to try it, as most old boatmen would advise.
Air draft is variable, as it depends on the shape of the bridge. A stone arch bridge may have sufficient headroom in the centre, but insufficient at the sides, while modern flat bridges may be lower than arched bridges, but offer better headroom over the whole channel. For arch bridges, Leigh Bridge is one of the lowest, with that at Shipley being one of the lowest flat bridges. Note that this bridge tapers downwards to one side. A clear height of 7 feet 10 inches sometimes quoted, but slightly higher boats may be able to pass if they have narrow cabins. Care should always be taken by boats approaching the quoted headroom as canal levels can also rise and fall.
In 2004 the Society, through the efforts of Mike Clark, produced a short leaflet "Boat Decoration on the Leeds & Liverpool Canal" covering L&LC traditional painting and it is available here
Publications coverering British Canal Art
There has been a small number of commercial publications covering British canal art and boat decoration - so a search on the web, the high street and your local library should find at least one or two. Some are now out of print but these publications were still available at the start of 2016