The Helena Gage reads 2.3 feet. The high point on your towboat is 26 feet above water. What is the vertical clearance when you pass under the Helena Highway Bridge?
• 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
• 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?
• 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.
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