Hakata -> Iki -> Tsushima (4 a day) 10 minute stopover in Iki.
Hakata -> Iki: 2:20 minutes
Iki -> Tsushima leg: 2 hours
One way prices:
Hakata -> Iki, 3720yen first class, second 2670yen, ordinary 1870yen
Hakata -> Tsushima, 7160yen first class, second 5240yen, ordinary 3580yen
From Hakata Port Terminal 2 at Bayside Place: just past the main Bayside Place shopping area/local ferry terminal you will see a green building on your right. That is Terminal 2.