SHEILA O’HARA II is a cargo oil tank barge owned by O’Hara on long-term charter for Boston Towing and Transportation (BTT). Built in 1985, the barge is 52′ long, 30′ wide and 8′ deep, with a raked forepeak void, port and starboard aftpeak voids, and four (2×2) cargo tanks. While SHEILA O’HARA II is not due to be retired until 2015, BTT contracted JMS to develop the concept design for adding a double hull at this time due to customer demand. Lacking any previous drawings, the first step was to perform a complete on-site inspection and develop as-built drawings to document the existing structure. Although the vessel is not classed, the double hull concept was designed to meet ABS Inland Rules with the double hull breadth and depth increased over the USCG requirement to permit access. The new double hull tanks will be used as voids.