Submarine design, for the past several decades, has sacrificed safety for speed, the enhancement of electronics, noise reduction, and depth. Recent efforts to increase performance resulted in a 9000 ton attack submarine. Dr. Heller asked What Price Depth? (USNI Proceedings, December 1975), wherein he defined the price of increased structural weight and its impact upon design. The elimination of multiple pressure holding bulkheads was among the give-aways. Are we now prepared for the payback? In the January 1994 issue of THE SUBMARINE REVIEW. Captain Khudyakov, Doctor of Technical Services, Russian Navy. carefully reviews the design and operation of submarine ballast tanks in his paper Is the Middle Group of Ballast Tanks Really Necessary on Submarines? The Los Angeles class is singled out, quote, “The quantity of sections in this class is reduced to three, which makes it impossible for her to stay on the surface when even an insignificant area of it’s section is flooded.” Several other high risk scenarios are also noted that would appear to demand amidships as well as fore and aft ballast tanks. In particular, the difficulty in controlling pitch in shallow water and at slow speeds. This causes one to question if such designs are appropriate for littoral missions. More to a point, he asserts, “The design should provide a balanced, stable, surfaced position if one of the main ballast tanks, in one of the ends of the submarines, is damaged. (This type of damage can occur at any time, for example, during a collision)”. He closes with three questions: “1) Is it possible to do without the middle group of ballast tanks? 2) Is it necessary to design single hull submarines with their main ballast tanks located in the extreme ends of the hull, and having only a small buoyancy reserve? (20 percent or less), 3) Is it worth considering increasing the effectiveness of the pressurized air system?” I believe the answer to these questions to be negative in all cases. Side saddle ballast tanks, applied to the Los Angeles class submarines, would have reduced their length by as much as 60 feet and the wetted surface by 15 percent. The potential for increased operability is evident and the negative impacts appear to be acceptable.
The apparent end to the Cold War provides a window of opportunity for the application of creative design and innovation to fully answer these questions, and restore survival and safety in the process. Increased compartmentation is restricted by the enormous weight of full diameter bulkheads. Even with the super strength metallurgy now being employed, greater displacements would normally be anticipated to accommodate them. Technology is at hand however that will allow a reduction of hull structural weight, add compartmentation, restore amidships ballasting, and effect cost reductions in many ship systems as well as achieving a better submarine at a lower cost.
What design change can bring about such significant advancements? Several alternate pressure hull designs have been suggest-ed which avoid many of the design problems common to most single hull submarines. They have significant potential for greater structural efficiency. Toroids and elongated ellipsoids have nearly twice the structural strength. The spheres used for most research submarines are capable of twice the depth for an equal plate thickness of identical material. This use of these compound curved surfaces is a means to achieve current operating depths with 50 percent less structural weight, and also cut welding costs by a similar proportion. This would make this an affordable submarine.
The realization that the Soviets were able to exceed the Trident’s displacement by as much as 60 percent in a hull of equal length suggests a new dimension of undersea architecture. This is accomplished by the broadened beam of the Typhoon with two parallel pressure hulls enclosed within an outer protective hull. The smaller length/width ratio provides a reduction in drag, primarily through a decrease in wetted surface. A flattened oval cross section results in a reduced vertical profile. In addition to accommodating amidships ballasting this arrangement reduces the risk of pressure hull penetration. The greater structural weight, twin propulsion plants and added reserve buoyancy, all increase displacement but this can be substantially counteracted by innovation. Preliminary testing suggests that a hydrodynamic hull form similar to this has superior stability, and is also more maneuver-able. Further tests are scheduled and should establish this to be a better submarine.
The agility to maneuver out of harm’s way has long been important to the safety of submarines. This capability is deter-mined by the static and hydrodynamic design of the vessel. Its control surfaces establish the rate of response but also contribute to its resistance drag. Greatest control is required for slow speed maneuvering but only minimal control is required at higher speeds, suggesting retractable surfaces. The reported tendency for snap roll in high speed maneuvering is endemic to current design practice. Elimination of the fin shaped sail can reduce this contributing source but also adds a requirement for a surface to counter the screw-induced roll. The introduction of an elliptical cross section would resist this torque without an increase of appendage drag. This problem is discussed by Henry E. Payne Ill and William P. Gruner, Naval Institute Proceedings (July 1992), and also by Theodore L. Gaillard Jr. in the SUBMARINE REVIEW (April 1993) Submarine Design: Aeroengineering Dimensions. In his article in Naval Institute Proceedings (April 1993), 1he Albacore: Back to the Future, Mr. Payne illustrates the difficulties of length in the shallow water environment. It is evident that a greatly shortened, flattened ellipsoid design with a Los Angeles displacement would embody the advantages of both and the limitations of neither. The next generation submarine must embody the goals of survivability, safety and performance at a lower cost.
A neglected aspect of submarine safety is accented by the Soviet submarine KOMOSOLETS having an escape chamber able to bring survivors up from the floor of the Norwegian Sea. Despite their difficulties with its separation and with toxic fumes, the pod withstood the pressures and bottoming impact and returned them to the surface. This type of ejection system has not been attempted by others and is long overdue. We do not send aviators into combat without parachutes. The finality of uncorrectable negative buoyancy is an unacceptable risk when crew escape is achievable. The next generation submarine must disregard price when the cost is in human life. This indeed will be a safer submarine.
