leadsman

He slowed the freighter to a snail's pace when he approached the dredged channel, and at last the leadsman found suitable bottom.

At a signal the leadsman had flown his pigeon again, though we were well past all reefs.

Then came the leadsman's long-drawn chant, once so familiar, the monotonous repeating in river parlance of the depths of water.

A leadsman had been stationed on each side of the forecastle, though there was no present occasion for their services.