On which vessels may credentialed individuals be required to stand watch under the two-watch system, on voyages of more than 600 miles in length?

Correct Answer: Option C — Uninspected towing vessels

46 CFR 15.705(c) specifically addresses the two-watch system for uninspected towing vessels. On voyages exceeding 600 miles, the Master may be required to maintain a two-watch system to ensure adequate rest and operational safety, reflecting the unique, often continuous nature of towing operations compared to other vessel types.