noun
maritime pilot; harbor pilot
A professional who guides ships through dangerous or congested waters, such as harbors or straits.
水先案内人が大型船を港へ誘導した。
The maritime pilot guided the large vessel into the harbor.
Compound of 水先 (mizusaki, 'course of a ship') + 案内人 (annainin, 'guide'). The exact historical derivation is uncertain, but the term has been used for maritime pilots since the Edo period.