As you pass under the Natchez-Vidalia Dual Bridge, the gage on the bridge reads +3.6 feet. If the highest point on your vessel is 62 ft. above the water, what is your vertical clearance?
• How a bridge gage is used to find available clearance under a bridge • Relationship between the gage reading, the charted clearance, and the air draft (height of the vessel) • Basic subtraction to find vertical clearance between the top of your vessel and the lowest part of the bridge
• Ask yourself: Does a positive gage reading mean the water is higher or lower than the reference level for the charted clearance? • Think about whether you should add or subtract the gage reading from the bridge’s normal clearance to get the actual clearance at this moment. • Once you know the actual clearance under the bridge, what simple calculation gives you the space left between the top of your vessel and the bridge?
• Be clear on what the +3.6 ft gage reading is telling you about water level compared to normal pool or reference level. • Confirm whether the bridge’s standard (charted) clearance is implied or needs to be inferred from the answer choices and the vessel height. • Double-check that your final step is (clearance under bridge) minus (vessel height), not the other way around.
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