Future growth margin is the real issue

I would like to take up Stan Weeks’ challenge in his article on “Density as a Ship Design Factor.” Stan references a U.S. Government Accountability Office report. Those interested can find it on line here. Concerns expressed with the Arleigh Burke-class (DDG-51) Flight III design option not only relate to stability issues from a rise in the centre of gravity and the effects on machinery caused by the new Air and Missile Defense Radar (AMDR), the class has a history of hull structural issues that raise the question how far the design can be safely modified. Modifying a ship design is an important issue for all navies. The RCN faced similar design challenges during the TRUMP modifications to the Iroquois-class destroyers. Navies will continue to face these problems if ships are operated beyond the traditional 25 to 30-year life planned in design.

The DDG-51 project team’s decision to build such a ‘dense’ ship was the topic of many discussions in my naval architecture classes at MIT in 1989. The USN professor at the time had been involved in many of the early design decisions. As in all ship acquisition projects, the final design was influenced by many factors outside the control of the designer. In the case of the DDG-51, U.S. lawmakers had imposed a maximum length on the design, ostensibly as a metric to contain costs. When politicians limit length, the logic went; ship capability and cost will be contained. It was like throwing a gauntlet to the USN and the consequence was a short, wide, very dense, yet very capable ship with design parameters that were outside all traditional values. Do not underestimate the design effort required to achieve the level of design density of the DDG-51. Similar logic limiting ship displacement (weight) as a criterion has been applied in the past with not so different results on design efforts.

Unfortunately, as Stan Weeks points out, the consequences for Flight III are significant. The design density issue is a particular problem for the DDG-51 design, though a lesson does exist for other navies in the example. It is obvious the original DDG-51 designers sacrificed future growth margins to achieve their desired capability within a maximum ship length. When future growth is part of the ship design requirement it costs money. It is also one of the few areas in a design that can be reduced or eliminated without compromising a ship’s present mission. The price of reducing future growth is paid in reduced flexibility and adaptability later in life, and in increased costs of modernization and upgrades. This is the real issue for the DDG-51 that can be taken to other navies.

Of broader concern to navies is any trend to compromise future growth capacity for immediate project-based acquisition concerns. No matter how effectively a ship’s hull, machinery and combat system are managed in service, it will experience weight growth and a rise in the centre of gravity as it ages. This will detrimentally affect hull strength and stability. We had theses issues with our TRUMP upgrades to the Iroquois-class and our Halifax-class frigates are currently facing them in their mid-life refit. It is unfortunately inevitable.

We should avoid very dense ship designs for the reasons that Stan identifies, but we should not rest on our laurels if our ships are less dense. Any ship with a limited growth margins will experience problems as it ages. It is a call to designers of future Canadian naval ships not to forget the long-term impact of neglecting future growth requirements.

As a Naval Engineer, I know that ship density correlates with engineering effort, so I like to draw another conclusion from the DDG-51. No one should ever underestimate the capacity of engineers to find a solution no matter what the constraints. Be careful what you ask for!