🔍 Key Concepts

• Bridge vertical clearance tables on the inland river charts for the Helena Highway Bridge A-span • How to adjust charted vertical clearance using the river gage reading (add or subtract correctly) • Relating the resulting clearance to the height of your vessel (32 ft) to see how much room you have above your highest point

💭 Think About

• Look up the charted vertical clearance for the A-span of the Helena Highway Bridge at the reference gage level. How is that clearance affected when the gage shows +6.6 feet? • Think about whether a higher gage reading means more air draft clearance or less. Should you be adding 6.6 ft or subtracting 6.6 ft from the charted value? • After you adjust the bridge clearance for the +6.6 ft gage, compare it to your towboat’s 32-ft height. What is the total vertical distance from your highest point up to the bridge?

✅ Before You Answer

• Verify the reference gage and stage used for the published bridge vertical clearance for the A-span (often at zero or a specified stage). • Double-check whether the gage correction is applied to the water level, not directly to the bridge, and how that changes the air gap. • Confirm that you correctly compute the remaining space above your 32-ft height after adjusting for the actual river stage.