There are few shipbuilding firms left in the United States, and Navy contracts are sometimes the only way they can stay in business. Even so, the Navy has refined its procurement procedures to transfer most of the risk to the shipbuilder. The Navy will supply the basic specifications, but the “yard” is left to design it all as one package, and there can be significant penalties for overweight ($250,000 per 10-ton increments) and for overshooting center-of-gravity (CG) height ($1.25 million per 10th of a foot over the limit). CG is critical to a ship’s stability both when loaded and when empty. The CG of a ship always remains the same, the idea being to return a ship to the upright position. The center of buoyancy, on the other hand, changes constantly, and a lower CG counteracts the negative effects of buoyancy.
Ships vary in buoyancy depending on how weight is distributed, and this contributes to bending which stresses the hull. All these factors have to be taken into account, and the addition of a flight deck to the design of a DDG (frigate) at the Navy’s request can result in thousands of additional manhours to perform the necessary calculations. Ship design is made even more complicated because of the curving nature of the hull. Each piece must be designed to mate to a non-uniform, uniquely curved piece of steel, so each piece has to be individually designed for where it is to go. Everything has to be drawn in three dimensions. Each welder gets an order from the Molding Loft
(where in full-size tracings used to be made of parts now drawn on computer) that describes each piece -- thickness, size, material. The Molding Loft also provides a welding plan that guides the “order of welds, directs the type of welding machine and flux to be used, shows how to bevel the edges of unequal thickness and how they should be oriented. It also includes a drawing of the final product as well as a record of where the part has been, where it’s going and every process that has been inflicted to it along the way. . . .”
The major portions of the ship are all prefabricated in huge buildings, and they are built upside down. Since most of the wires, pipes and fittings are installed in the ceiling, it’s easier on the workers to weld down rather than over their heads, so the construction proceeds much faster. But it’s disconcerting to walk through doors that are upside down. Then enormous cranes are required to lift the sections onto the keel, where they must fit together precisely and are welded in place. Extraordinary.
The launch, sliding down the ways, is an intricately choreographed ballet of men performing all sorts of difficult and dangerous activities. Failure of any one of the individual parts might cause disaster. Weather can also be a factor, causing the tallow and wax to be harder and not slippery enough, or the wind might be too strong, blowing the ship around in the water— it is, after all, a helpless hull presenting a huge surface to the wind. Usually, when things do go wrong, it’s rarely because of one major failure; it’s the accumulation of effects from several smaller mishaps that together spell disaster. Each launch becomes a tricky birthing with nail-biting anticipation and thrills. There is no reversal. Once the ship begins to slide, there is no way to stop and a failure would spell the end of the shipyard. Sanders describes the launch of the Main, the largest ship ever floated on the Kennebec River, which very nearly capsized off the ways. One critical point is when the stern enters the water and becomes buoyant. This forces the bow down into a special device built specifically to gradually take the additional
pressure by collapsing. If it were not there, the strain would break the ship in the middle. In the case of the Main, special saddles had been built to help relieve this strain, but one exploded causing two others to break, and for several moments there was nothing to prevent the ship from falling over. It was a very tense moment.