June 2002 Excerpt
Groundbreaking High Speed Sealift Design Tested in MASK
By William Palmer
model of a high-speed design for an ocean-going transport trimaran continues
its testing in the Maneuvering and Sea-Keeping (MASK) facility at Carderock.
The testing of this groundbreaking design is the latest in an ongoing effort
to fuse technological advances on several fronts with transportation demands
posed by military and maritime customers.
The concept for this design evolved from a week-long High Speed Sealift Technology Workshop held in 1997. The workshops goal was to bring together government, academia, and the maritime industry in an effort to assess new technologies with more strenuous industry and military transport requirements. More than 200 people representing 12 countries and manufacturers, such as Rolls Royce and General Electric, participated in the workshop. Committees were formed to ponder the technical possibilities of combining hull designs, new materials, and advanced propulsion systems to fit a new transportation paradigm.
The new paradigm is simple yet demanding: move a large amount of cargo across an ocean as quickly as possible using new-design hullforms. Since the new designs are truly innovative in nature, there are no data to corroborate many design decisions. A crucial feature of this work is that it has an ongoing program of real-time testing to verify the design.
The designs, which have addressed the structure of this new direction, are varied in their scope. Teams of engineers, designers, and computational systems specialists, comprising a design group called the High-Speed Sealift (HSS) Innovation Cell collaborated on the development and assessment of about 50 point designs, which addressed the new challenge. One of these designs, a water jet-propelled trimaran, has advanced to model status and tow tank testing. The model has a long and slender hull, with a pair of short outriggers at the aft endso short that they comprise only 2% of the buoyancy of the hull. The self-powered model is propelled by two electric motors, which drive four waterjets through combining gearboxes. The bow of the trimaran is shaped so that it presents minimal flow resistanceand thus avoids the force ofan oncoming wave.
A more conventional design would have higher loads and more structure, and therefore more mass, in the bow. Since weight is a critical component in a high-speed application, it was decided to do away with the extra mass and instead re-shape the hull. An aluminum beam traverses the length of the model at its center and has the function of simulating the strength properties of the ship in the model. The model hull itself is cut into six major segments, which are attached to the beam with the individual segments connected to each other only by watertight rubber seals. This is done to measure the pressures and loads being imparted to the individual sections. The model, including the beam, is designed to simulate the full-scale ship with a full load of fuel and cargo and the rigidity of the hull.
Dr. Colen Kennell (242), a naval architect and self-described caretaker of the project, is providing the technical direction of the HSS Innovation Cell. He is also managing the foreign exchange program associated with the project. He cites two examples of the need for high-speed transport: Third Marine Expeditionary Force exercises in Okinawa and the massing United States forces in Kuwait to counter the Iraqi invasion of that country during Operation Desert Storm. In the case of the Marine exercises, because of political complications, the exercises had to take place away from Okinawa. An airlift was initially considered as a means of transporting troops to remote exercise areas, but expense and logistics problems were encountered. A catamaran transport, capable of a 38-knot top speed, was leased for the task and proved very successful in its transport role. Regarding the Desert Storm operation, Kennell says it took 100 days for the strength of U.S. forces in that area to reach a critical mass. Had high-speed transport been used, that time of amassing troops in such a remote area could have been reduced considerably. Asked if there is a parallel between the transition of technology and function this design represents and the transition of maritime technology from sail to steam, Kennell commented that the sail-to-steam change was revolutionary, one of liberation, allowing vessels to be steered anywhere without reliance on the wind, whereas the current design effort constitutes an evolutionary refinement to achieve higher efficiency.
We are creating a set of brand new yardsticks for this project, he said, and the project is radically different than any of its kind. The model being tested now is an analogue of a vessel planned to be 1,060 feet in length, displacing 27,000 tons, and with a top speed approaching 60 knots. Kennell commented that the model currently undergoing testing in the MASK at speeds up to 55 knots, with simulated oblique seas, is very stable. At these high speeds, only six to 10 seconds of usable data can be gathered. The self-powered model is rigged below the carriage such that it is free to move in response to simulated wave motion. It is tethered to the carriage by two single lines fore and aft and a centrally located telemetry cable bundle, but the constraints to motion are considered negligible. Kennell sees this testing as a benchmark to be used for further research and design and could be useful to a lot of people in a lot of different ways, he said.
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