Your probably looking at the Vashon to Seattle Passenger Ferry Schedule... which has limited runs... like three in the morn and three at night...
The Car Ferry runs much more frequently but drops off in West Seattle, fauntleroy. then a 30 min drive to down town Seattle.
http://www.wsdot.wa.gov/ferries/schedules/current/index.cfm?route=f-v
Ohhh, cool!