🔍 Key Concepts

• Vertical clearance is the distance from the water surface to the lowest part of the bridge span • How river gage readings relate to a charted or reference clearance at a specific gage height • Whether you should add or subtract the boat’s air draft (46 feet) from the available clearance under the bridge

💭 Think About

• Think about what the gage reading is telling you: if the river is higher than the reference level, does that make the bridge clearance more or less? • If you know the distance from the water to the bridge, how do you use your towboat’s 46-foot height to determine if you can safely pass? • Which operation (addition or subtraction) correctly combines the gage-based bridge clearance with your vessel’s height to get the remaining vertical clearance above your highest point?

✅ Before You Answer

• Be clear on whether the question is asking for clearance under the bridge or clearance above your vessel as you pass • Confirm that you’re consistently using feet and that you only combine values that represent compatible distances (water-to-bridge vs boat height) • Double-check if you are using the gage reading in the same way it would be used in a bridge clearance table (does an increasing gage reading increase or decrease clearance?)