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Defense News: Will DDG-1000 Destroyers Be Unstable?
The military is by nature a conservative community. Given the cost in lives inherent in betting on the wrong new trend, this should hardly be surprising. Sometimes, that traditionalist streak gets in the way of progress, as was the case with radical ideas like the aircraft carrier. Sometimes, the skepticism is justified. Defense News looks at the $3+ billion per ship DDG-1000 Zumwalt Class, which is likely to serve as a design template for future cruiser classes (CG-X, 19 ships from 2011) and possibly even a frigate class (FFG-X, featured in CBO reports but no firm plans), asking: "Is New U.S. Destroyer Unstable? external link" Are the critics prisoners of their preconceptions re: what ships are "supposed" to look like, or sounding an early alarm before a very expensive ship and its crew are lost to Mother Nature rather than enemy fire? Defense News:"Nothing like the Zumwalt has ever been built. The 14,500-ton ship's flat, inward-sloping sides and superstructure rise in pyramidal fashion in a form called tumblehome. Its long, angular "wave-piercing" bow lacks the rising, flared profile of most ships, and is intended to slice through waves as much as ride over them..." "At least eight current and former officers, naval engineers and architects and naval analysts interviewed for this article expressed concerns about the ship's stability. Ken Brower, a civilian naval architect with decades of naval experience was even more blunt: "It will capsize in a following sea at the wrong speed if a wave at an appropriate wavelength hits it at an appropriate angle"... " "...Brower explained: "The trouble is that as a ship pitches and heaves at sea, if you have tumblehome instead of flare, you have no righting energy to make the ship come back up. On the DDG 1000, with the waves coming at you from behind, when a ship pitches down, it can lose transverse stability as the stern comes out of the water -- and basically roll over." These concerns have existed for a decade, but the US Navy continues to express confidence in the stealth-enhancing design based on their modeling and testing to date. A 1/20 scale, 30-foot scale model has been taken it up through Sea States 8-9 [hurricane-force seas and winds], based on the standard US Navy requirement for stability in ships is a 100-knot wind and using a model of 1969's Category 5 Hurricane Camille. A 150-foot, 1/4 scale steel hull has also been built and tested for stability, and the arm's-length US Naval Technical Authority has determined the Zumwalt's design to be safe. All ships may face dangerous conditions at sea, and all ships have conditions in which certain actions can be troublesome of even dangerous. Ships larger than the Zumwalt Class have gone to the bottom in freshwater lakes, let alone the open ocean. They key issue is that no ship with the same set of design features has ever put to sea... and those that were similar didn't do well. A number of French and Russian battleships used tumblehome designs, and their poorer sea-keeping abilities were a matter of record. The tumblehome design's repute was not enhanced when several Russian battleships sank after being damaged by gunfire in the 1905 Battle of Tsushima. In fairness, one must note that the Russian ships suffered from "having their 'T' crossed" by Japanese maneuver; to which must be added unhealthy crews, poor quality shells, poor training and tactics, and a high rate of casualties among the force's commanders. Regardless, the tumblehome hull form was dropped by French designers after World War 1. Unsurprisingly, concerns also persist about the Zumwalt Class ships' ability to take damage. The sharply reduced crew size of just 182 promises operational cost savings and instant response, but automated damage control mechanisms coordinated by software remain an unproven option. In exchange for its advantages, it may offer less adaptability than human crews are capable of, as well as a potential point of failure in the automated systems themselves or their software. In the end, the "unproven" label remains the core issue facing the DDG-1000 design, on multiple levels. It is new, and unlike more conventional hull forms it has not encountered tens of thousands of sea states and combat injuries to provide a deep baseline for prediction and modeling. Testing is underway with the best will and equipment available -- but no testing program can truly duplicate the vast legacy of experience built up during the last century with conventional hull forms. Ship design has come a very long way since 1905, and an era of aircraft and missiles creates different imperatives for performance and survivability. The US Navy argues that a new approach is needed because existing designs are too limited, and sees a new design that would be difficult to copy and give its ships the edge in combat. Critics argue that inaugurating a completely new hull form, on such an expensive ship, creates real risks of untested events or combinations that could lead to the catastrophic loss of a major fleet asset. Not to mention the end of a hugely expensive program, long after vast sums have been expended. Who's right? The answer could easily be either party, or neither party -- or even both parties. Until the Zumwalt Class' hull form is truly tested with a baseline of at sea experience and with experience of severe damage, we won't really know. Meanwhile, decisions must still be made, in an arena that's all about assessments of risk and advantage. Posted by: gorb 2016-02-02 |
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