🔍 Key Concepts

• Dual tonnage applies to vessels that sometimes load to different depths depending on the waters they operate in (e.g., inland vs. foreign voyages). • Dual-tonnage marks relate to net and/or gross register tonnage assignments, not displacement tonnage. • The physical location and purpose of the dual-tonnage mark in relation to load line marks and draft changes.

💭 Think About

• Which types of tonnage are normally used for regulatory and documentation purposes: displacement, gross, or net? • Would a draft mark or tonnage mark that ‘must never be submerged’ make sense if the vessel is expected to load deeper on certain voyages? • Is there any structural reason a single-deck vessel could not be assigned two different regulatory tonnages based on its loaded condition?

✅ Before You Answer

• Verify what displacement tonnage measures versus gross tonnage and net tonnage. • Think about how dual tonnage allows a ship to have one tonnage assignment at a shallower draft and another at a deeper draft. • Consider whether a dual-tonnage mark must always be above the load line marks, or whether its position can vary depending on which draft corresponds to which tonnage.