🔍 Key Concepts

• air draft (height of the vessel above the waterline) • How bridge vertical clearances on inland rivers are tied to the local river gage (stage) • Using the formula: available clearance over your boat = (bridge clearance at that gage) − (your boat’s air draft)

💭 Think About

• First, think about what the Natchez Gage reading tells you about the river level and how that affects the bridge clearance compared to low water. • Look up (or recall from your exam reference tables) the vertical clearance of the Natchez Highway Bridge at the current gage reading of 20.6 feet. • Once you know the bridge clearance above the water, subtract the 47‑foot height of your towboat to find how much space is left between your highest point and the bridge. • Compare your calculated clearance to the answer choices and see which one matches most closely.

✅ Before You Answer

• Be sure you are using the correct bridge clearance table for the Natchez Highway Bridge (Natchez, Mississippi River). • Confirm that you are subtracting the towboat height (47 ft) from the bridge clearance above the water surface, not from the gage height. • Double‑check unit consistency: all heights should be in feet and referenced to the same water surface level.