A car ferry itself does not require a vignette. What matters is the road you drive on after disembarking.
If you leave the ferry and drive only on non-motorway roads (e.g. local or cantonal roads) a vignette is not required. As soon as you enter a motor or express way a valid vignette is required. Driving even 1km or 1 minute without a valid vignette there can result in a heavy fine.
Related articles:
Can I drive in Switzerland without a vignette if I avoid motorways?
What happens if I drive without a Swiss vignette?
Are shorter term Swiss motorway vignettes available (daily/weekly/monthy)?