Small passenger boats including kayaks, pedal boats, electric powered pontoons and fishing boats. Crude oil was pumped ashore from tankers moored at deep-water pontoons. Such long bridges required support from either piers or pontoons. The M4 bridge featured a lightweight aluminum balk deck supported by rigid aluminum hull pontoons. External brackets built into the bulkheads transfer the support forces to the pontoons. Alighting can be supported by a hull-shaped fuselage and/or pontoons. Common boat designs are a catamaran with two pontoons, or a trimaran with three. The hull consists of two pontoons with four columns each. The operation saw "Ocean Ranger" towed upside down with her two pontoons breaking the surface. It was floating on two long pontoons that rested below the surface. These comprised pontoons linked to the land by floating roadways. The roadway is constructed atop these concrete pontoons. A marina was started in 1979 by dredging the upper harbour and laying pontoons. Structural columns connect the pontoons and operating deck. The watertight doors for the pontoons were therefore removed.