I play continents+. Compare water scouting options:
- Work boats - 5 movement, 40 hammers, can temporarily traverse ocean, can share a tile with other civs' military units, can't defend themselves but are generally lowest priority targets / will not be attacked at all, does not cost military unit supply
- Trireme - 4 movement, 90 hammers, can temporarily traverse ocean, can't share a tile with other civs' military units
- Scout/other land unit - 3 movement, cannot traverse ocean, 1 sight range, can hop off and claim goody huts, sitting duck if hit by barbarians at sea.