In the diagram, items '2A and 2B' represent the overboard discharge valves of the ballast system illustrated. According to 46 CFR Part 56, which of the following statements is correct if the length between perpendiculars of a vessel is 500 feet, and the through hull opening is eleven feet above the summer load line? See illustration GS-0125.
• 46 CFR Part 56 ballast and overboard discharge piping requirements (look especially at overboard discharges above the summer load line). • Difference between a positive closing valve (manually operable shutoff/sea valve) and an automatic non-return valve (check valve). • How the vertical distance of the opening above the summer load line affects what kind and how many valves are required.
• From the illustration, which valve (2A or 2B) appears to be the check valve and which appears to be the manually operated stop/sea valve? • According to 46 CFR Part 56, when an overboard discharge is more than a specified distance above the summer load line, is a positive closing valve at the shell still required, or can a non-return alone be accepted? • Does the regulation talk about needing both a positive closing valve and a non-return valve, or can one of them satisfy the requirement when the opening is sufficiently high above the load line?
• Verify in 46 CFR Part 56 the exact vertical distance above the summer load line that changes the valve requirement and compare it to the 11‑foot value in the question. • Confirm from the diagram which side of the shell (hull) each valve is on and which symbol corresponds to automatic non-return versus positive closing. • Check whether the regulation requires a second valve or additional feature when the vessel’s length between perpendiculars is 500 feet (vessel size can sometimes change the requirement).
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