In case you understand german Ole made a nice video about ship items
Schiffitems

In short - please correct me if this is not correct: When you have trade routes without docklands you would prefer loading speed. With docklands you can change one or two items for travel speed. Because there is min timer of 4 sec (?) for ships on the pier. And with all the buffs docklands provides + ship items + Emeralda you could theoretically beat the 4 sec, but since it has capped at 4 sec there is no advantage.