You are here

Lightweight Gearbox for Air Cushion Vehicles



OBJECTIVE: Develop a lightweight gearbox for Air Cushion Vehicles (ACV) that reduces fuel consumption and improves maintainability. 

DESCRIPTION: The Ship-to-Shore Connector (SSC) is an Air Cushion Vehicle (ACV), or “hovercraft”, providing amphibious transportation of equipment and personnel from ship-to-shore and shore-to-shore. Development of a performance-improving, robust, maintainable, lightweight (max. 4,730 lbs), and variable-speed gearbox is paramount to SSC operation. The craft contains two gearboxes (port and starboard), each combining high-speed inputs from two longitudinally mounted engines to power a single lift fan forward and a single propeller aft. The gearbox transfers approximately 12,000 Shaft Horse Power (SHP) with speed reduction ratios approximately 12:1 for the prop and 8:1 for the lift fan. Each gearbox interfaces with Engineering Control System (ECS) and craft lubrication oil system. Any changes to the gearbox design interfaces need to take into account the current craft configuration and asses the overall impact. The gearboxes are in constant use whenever a craft is operating, and any increase in efficiency and decrease in required maintenance is valuable. The intent of this effort is to decrease the weight of the current gearbox design (4,730 lbs) and remain within the existing gearbox space envelope of approximately 75” Long x 50” deep x 93” high while minimizing the overall impact to existing auxiliary support systems and sub-systems. Along with decreasing the weight, making a more serviceable gearbox would lead to decreased repair costs. Typically, each major repair requiring gearbox removal requires approximately 200 labor hours and Depot Level repairs can cost up to $100k. Additionally, an innovative new gearbox design providing multi-speed functionality would allow for increased efficiency during lighter loads and enable an overall reduction in fuel consumption. The lift fan has a fixed geometry and is the primary power consumer in the SSC drivetrain. Current SSC gearboxes have a single output speed. By allowing for multispeed functionality for the lift fan, the powertrain can be optimized for environmental and cargo conditions. The new gearbox design must be compatible with the current craft configuration regarding form, fit, and function, requiring minimal adjustments to surrounding equipment and support the PMS 377 LCAC Lightweight Gearbox Design specifications (Ref 5). 

PHASE I: Define and develop a concept for a new gearbox for SSC that meets the requirements as described above. Demonstrate the feasibility of the concept in meeting Navy needs and also demonstrate that the lightweight gearbox concept can be readily and cost-effectively manufactured through standard industry practices by material testing and analytical modeling. The Phase I Option, if awarded, should include the initial layout and capabilities to build the prototype in Phase II. Develop a Phase II plan. 

PHASE II: Based on the results of the Phase I effort and the Phase II Statement of Work (SOW), develop and deliver a prototype lightweight gearbox for evaluation by performing a 100 hr loaded cyclic test in accordance with MIL-G-17859. Evaluate the prototype to determine its compatibility with current craft layout and ability to perform to requirements. Demonstrate system performance at the power train test site before installation on a SSC Test Craft. Use evaluation results to refine the prototype into a design that will meet the SSC Craft Specifications. Prepare a Phase III development plan and cost analysis to transition the technology to Navy use. 

PHASE III: If Phase II is successful, support the Navy in transitioning the lightweight gearbox for Navy use on the ACV program. Refine the design of the gearbox, according to the Phase III SOW for evaluation to determine its effectiveness in an operationally relevant environment. Support the Navy for test and validation in accordance with Craft Specifications to certify and qualify the system for Navy use and for transition into operational SSCs. Following testing and validation, ensure that the end design will provide an overall lower-weight, variable-speed lift fan with increased maintainability, reduced fuel consumption, increased efficiency, and compatibility with existing systems aboard the craft. The SSC lightweight gearbox will have private sector commercial potential for hovercrafts of this scale operating in the near- or on-shore environment. Commercial applications include ferries, the oil and mineral industry, and cold climate research and exploration. Other industrial or military machinery in this power range like helicopters could also benefit from technologies developed during this effort. 


1: Mancini, Joseph H. "An Overview of Advancement in Helicopter Transmission Design."

2:  Segade-Robleda, Abraham, Vilán-Vilán, José-Antonio, López-Lago, Marcos and Casarejos-Ruiz, Enrique. "Split Torque Gearboxes: Requirements, Performance and Applications." University of Vigo, Spain.

3:  White, G. "Design study of a split-torque helicopter transmission." Cleveland, OH: Transmission Research Inc.

4:  Rashidi, Majid, and Krantz, Timothy. "Dynamics of a Split Torque Helicopter Transmission." Cleveland State University, Lewis Research Center.

5:  PMS 377 LCAC Lightweight Gearbox Design (uploaded to SITIS 11/29/2017)

KEYWORDS: Compact Gearbox; Ship-to-Shore Connector; Landing Craft Air Cushion 100; Fuel Efficiency; Hovercraft; Variable Speed Gearbox Lift Fan 


Lance Shappell 

(215) 897-1972 

James Lambert 

(215) 897-8672 

US Flag An Official Website of the United States Government