The ferry service to Suomenlinna is operated by the Helsinki Region Transport Authority (HSL). Depending on the season and the time of day, ferries run 1 to 4 times per hour, from the morning until the night throughout the year
Departure of Suomenlinna ferries from the Market Square and Suomenlinna usually once an hour. From the beginning of May through August ferries depart in daytime at shorter intervals, 3-4 times per hour. The ferry trip takes about 15 minutes. The Suomenlinna ferry is part of Helsinki’s public transport service.
Show your ticket to the card reader.
Suomenlinnan Liikenne Oy, Market Square
OPERATING TIMES 1.1.-31.12.
From Market Square daily 06.20-02.20
From Suomenlinna daily 06.00-02.00
More info: https://www.suomenlinna.fi/en/