Almost ten years after Richard Goldbach, of Metro Machine Corporation, patented the unique Marc Guardian double-hull design, hull sections are finally emerging from Metro’s shipyard on the shores of Lake Erie. The Marc Guardian design applies curved-plate technology to eliminate the stiffeners normally used to strengthen the hull plates. The hull derives its strength from the curved plates themselves. Two of these slightly convex panels make up the front and back of a cell, whose top and bottom are flat plate. Adjacent curved panels are connected at the flat plate in a three-way joint.
According to Metro’s Vice President Ralph Ryan, the design does not offer any significant saving in steel weight, since the unstiffened plates are thicker than would be the case in a conventional design. The advantages are found elsewhere. “The structure has much less corrosion potential, because it eliminates the stiffener welds and provides a smooth, uninterrupted surface. It promises to save tremendously on maintenance,” he says.
The production process is built around the design. The 50 ft raw steel plates are cut into the required 5-8 ft widths. The curved plates are set onto a specially-designed 52 ft magnetic bed of an Ingersoll milling machine, where plate edges are machined for welding. Special vacuum lifters then place them in the unique shaping press that imparts the required curvature. The curved and flat plates are then assembled into port, starboard, or bottom subassemblies. Again the approach is unique in that the plates are stood vertically within a massive jig and clamped precisely by some 1,200 hydraulic cylinders. The three-way cell joints (between the curved and flat plates) are welded in one 50-foot vertical pass using an electro-gas welder. The subassembly is lifted and moved to a module erection fixture, where five subassemblies are aligned and joined to form a 350 ton hull module. The section is then transferred to the 1,230-ft dry dock. ABS has played a significant role in the development of this unique design and construction concept.