Here is another way, which could be combined with other answers: make the planet cold, either permanently or because it's in the middle of an ice age.
The idea is that only the equatorial region is really suitable for human habitation. If you go too far north or south everything is covered in glaciers and the sea is frozen. Seen from space, the planet is more than half covered by white ice caps, with a blue-green band around the equator., something very roughly like this:
The Earth has probably been in this kind of state several times in the distant past.
Now since the continents are all clustered together, there isn't much point in using boats. The human-habitable region is a letter-box shaped piece of land that runs across a single large continent in the east-west direction. The climate there is temperate, but to the north and south it's bounded by icy wastes rather than ocean. It has coastlines to the east and west, but they're relatively short, and to get from one to the other you'd have to sail around the entire planet.
This would severely limit the usefulness of ocean-going vessels. If you had them you could use them to travel north-south along the coastlines, but this would provide a lot less economic benefit than it does on our world, so there would be a lot less economic pressure to develop them in the first place. If the coastlines are not rocky then your people might just build railways or canals along the coasts instead, and then never really feel the need to develop shipping beyond sport and fishing. (The latter of course only applies if there are edible fish.)