The highest point on your towboat is 67 feet above the water, and the Helena Gage reads +22.3 feet. What is the vertical clearance when you pass under the A-span of the Helena Highway Bridge?
• How river gage height affects bridge vertical clearance (higher river = less clearance) • Using the charted or signboard vertical clearance at 0.0 gage for the A‑span of the Helena Highway Bridge • Difference between clearance above the water and clearance between your tow and the bridge
• From the exam chart or bridge signboard, what is the A‑span vertical clearance at 0.0 on the Helena Gage, and how does a +22.3 ft reading change it? • Once you know the clearance from the water to the bridge at today’s gage, how do you use your towboat’s 67 ft air draft to find the remaining clearance? • Is the question asking for the clearance ABOVE THE WATER or the clearance BETWEEN YOUR TOW AND THE BRIDGE? How does that change which numbers you combine?
• Be sure you are using the A‑span clearance at 0.0 Helena Gage from the provided reference (chart or signboard) • Confirm you subtract the gage reading from the 0.0-gage clearance when the gage is positive (river above reference) • After finding water-to-bridge clearance, subtract your 67 ft height to get the vertical clearance for your tow under the bridge
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