EPA Vessel Hull Inspection

Location: 
Duluth, MN
Completed: 
2010, 2011, 2012, 2014

· EPA Research Vessel

AMI Consulting Engineers, PA was hired to develop and provide plans to replace an existing ship A-Frame on the research vessel Lake Explorer II, formally a 90-foot hydrographic survey vessel from National Oceanographic and Atmospheric Administration (NOAA), which was transferred to the USEPA to be used as a research vessel on the Great Lakes. The vessel is steel hulled, 150 Gross Registered tons, 220-ton displacement, twin diesel engine, two fixed propellers, and draft of 7 feet. The current stern A-Frame is not adequate for the ship’s new mission for towing larger science equipment from the stern of the vessel, hence the need to install a new stern A-Frame that has greater lifting capacity with more height and width.

The design for the A-Frame base is constructed of steel and designed to distribute the load across the ship’s deck efficiently. The A-Frame plan was to mount to the deck on the stern, in a U-shape and utilize hydraulic rams to raise and lower the A-Frame. AMI designed the hydraulic system with a balance of speed and power to meet the customer’s requirements and fit within the space of the old hydraulic system. The aluminum A-Frame legs were designed to pivot on stainless steel pins and were built to handle no less than 3000 pounds throughout its range of motion, with 5 times safe working load factor. It was engineered to handle this minimum load, while in static or dynamic loading conditions, and has the capability to handle side loading as well.  To minimize weight, AMI designed the A-Frame out of aluminum and utilized a FEA software to analyze the system and cut down on any unnecessary material.  With the increased load rating of the new A-Frame, a stability analysis was also performed to ensure the vessel would remain safe in the most adverse operating conditions. AMI evaluated the ship’s stern decking and framing for structural strength to support the static and dynamic forces exerted by the new frame.

Due to the increasing demands of research equipment, the EPA purchased a new knuckle boom crane for the vessel with a greater reach and greater load capacity.   AMI was contracted to perform a structural analysis on the vessel deck and redesign the vessel’s mast, making it more functional for use in the Great Lakes. The steel mast was mounted at a height of 18.5 feet above the top of the pilot house, with RADAR located atop of the mast and an antenna clearance of 6-foot diameter.  The new crane base design included a concealed passageway for the hydraulic lines to keep them protected and maintenance hatches for easy access