21 has Nat/Kat on the Star Ferry, not the Cheung Chau ferry. The Cheung Chau ferries are much wider.
This makes Star Ferry and the Central Piers the most visited attraction in all of TAR; it's been featured on six seasons! (TAR 2, TAR 11, TAR 17, TAR:A 2, TAR:A 3, TAR:I)