| Publication |
2014.
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| Summary/Abstract |
The Independence -class littoral combat ship (LCS) has a fundamentally different design from any other ship in the Navy. Understanding how its design affects propulsion, sea-keeping, and reactions to external forces is critical to understanding how to drive it effectively, efficiently, and safely.
The Independence -class LCS is propelled by four steerable water jets (WJs) that have independent drive trains. The two outboard WJs, driven by motor turbine union 20-cylinder main propulsion diesel engines (MPDE) rated at 12,200 horse power (HP) each, have the most impact on low-speed precision maneuvering due to their position off centerline. The two inner WJs, used for high-speed operations and restricted maneuvering situations, are driven by LM2500 gas turbine engines, each with speeds up to 29,500 HP. The ship develops thrust as water is drawn through intakes under the hull, travels through each WJ tunnel, and is driven at high speed through the WJ by an impeller.
Attached to each WJ is a hydraulically actuated reversing plate commonly referred to as a "bucket," which controls the amount of water directed forward or aft. When the ship's control console (SCC) indicates zero percent bucket, roughly one-third of the water is directed astern and two-thirds are directed forward and down, causing the applied longitudinal forces to cancel out. Even at this "zero-thrust" point, the impellers are still turning at idle speed, an important consideration for the effects of engine wash on surrounding vessels and structures.
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