Sailing
Even the most rudimental of seacraft require very specific knowledge, needing at least one person with proficiency to use.
Rowboat (50gp): A small rowboat, Able to fit 2 medium sized humanoids comfortably.
Two-Man Skiff (60gp): the smallest of sailing vessels, barely able to carry 6 medium humanoids and their packs. Requires at least 2 passengers trained in watercraft to operate, but can benefit by two additional crew, with can be untrained.