General:
* Journey
* Trip
* Expedition
* Excursion
* Cruise
* Travel
* Adventure
More specific:
* Sea voyage: Seafaring, sailing, navigation
* Space voyage: Spaceflight, orbital mission
* Long voyage: Pilgrimage, odyssey, epic
* Short voyage: Excursion, jaunt, trip
The best synonym will depend on the specific context of your writing.
For example, if you're talking about a long and adventurous sea journey, "odyssey" might be a good choice. But if you're simply describing a short trip on a boat, "excursion" would be more appropriate.