Most of the shanty singers/scholars state that shanties died out in the 1600's and 1700's because the ships were not in a hurry and their crews were large, and that it wasn't till the 1820' and 1830's that shanties began to be revived as shipowners began to try to keep their ships on a schedule and complete aggressively with other shipping lines, designed faster ships, and cut down crew size to save money; this is the shanty theory in response to the pressures of the new industrial market system. I still find it hard to believe that such a useful training tool as shanties weren't used in the 1700's, and that it seems more likely to me that no one thought they were interesting enough to write down.