I don’t think that there was much fixed scheduling for water transport prior to the the development of steam engines either, because you were usually at the mercy of the winds and the tides.

Rowing was common and well known. Many ferries cross rivers where tides and the wind are not concerns. Winds near shore are often consistent enough to have near fixed frequency routes.

Ancient Mediterranean maps often reveal ferries and such were not going vast distances but rather they would go from small settlement to small settlement. This would be much smaller boats that could be easily rowed and, in turn, have relatively fixed frequencies. The small boats could get into ports that would be impossible to put a large ship into. As ships grew larger and sailing became more popular, longer distances would happen and then winds and tides would be more important.

https://en.wikipedia.org/wiki/Trekschuit:

“Trekschuit (Dutch pronunciation: [ˈtrɛksxœyt] ⓘ; lit. 'tug-boat', i.e. 'tugged boat') is an old style of sail- and horse-drawn boat specific to the Netherlands, where it was used for centuries as a means of passenger traffic between cities along trekvaarten, or tow-canals.

[…]

By 1700, an extensive network of trekschuit- and ferry services linked all of the important cities in the coastal provinces of the Netherlands. Travel by trekschuit was reliable, comfortable, and cheap. The speed was about 7 km/h, which was faster than walking, and more comfortable than by coach. Many foreigners praised the advantages of the system, leading to the introduction of canals, such as the Erie Canal, in the United States. The boats were pulled along by horse on a towpath (in Dutch called jaagpad, named after the jager (chaser) which accompanied the horse)”

Scheduled sailings were common in the Roman world, and some medieval European economies. It helped keep ship sizes small when merchants could anticipate the fixed schedule.

Just dig a canal along the route you want, and use horses to pull the boat along it. See the other comments about the trekschuiten in the Netherlands.

That's right, I just read about that. Even crossing the English channel apparently was unpredictable at times.