🔍 Key Concepts

• Bridge clearance tables or charts for the Helena Highway Bridge and how they relate to the Helena Gage reading • How to calculate available clearance by starting from the bridge’s reference clearance and adjusting for the current river stage • Remember to subtract your vessel’s highest point from the available clearance to get the final safe vertical clearance over your towboat

💭 Think About

• Ask yourself: At what river level (gage reading) is the bridge’s published clearance given, and is today’s level higher or lower than that reference? • Think about whether a higher gage reading means more or less clearance under the bridge, and how that affects your calculation. • After you determine the clearance under the bridge at today’s river level, how do you adjust that number to find the clearance above the highest point on your towboat?

✅ Before You Answer

• Verify you know the standard reference gage height and corresponding bridge clearance used in your exam materials (often printed in a table or diagram). • Double-check that you applied the correct sign when adjusting for the difference between today’s gage reading and the reference reading (did you add or subtract correctly?). • Confirm that your final step subtracts the 26-foot towboat height from the bridge clearance at today’s river level, not the other way around.