CUVX Design Report - the AOE home page - Virginia Tech

CUVX Design – VT Team 2 Page 16propulsion generators for primary ship service power. Alternative 8 uses five diesel engines. Alternatives 10 – 14are two shaft configurations using different combinations of diesel, gas turbine, and ICR engines to span the targetpropulsion power range.Figure 4. CUVX Machinery AlternativesMechanical Drive and IPS systems – Both mechanical drive and IPS systems are considered in the machinerytrade-off. Important advantages of a mechanical system are that sub-systems and components are proven inprevious Navy ships and cost less than in an IPS system. Mechanical drive systems also weigh less and occupyless volume. The main disadvantage of a mechanical drive system is that it requires a direct in-line connection tothe propellers limiting arrangement and location options. Mechanical drive systems are often less efficient thanIPS because engine rpm at a given power is governed by the propeller rpm and reduction gear ratio, while enginesin an IPS system may be operated at optimum rpm for a given power output. Mechanical drive power can only beused for electrical power if some type of power-take-off system is installed. The main advantages of an IPS systemare the ability to locate propulsion engines and generators almost anywhere in the ship, and to provide bothpropulsion and ship service electrical power. The survivability of the ship also increases with shorter shaft lengths.Another advantage of an IPS system is that it can be used with a traditional fixed pitch propeller or poddedpropulsion system. The acoustic signature of IPS ships is less because the engines are not connected mechanicallyto the shaft and fixed pitch propellers have inherently lower signatures and cavitation than CPP. The use of fixedpitch propellers and the ability to run the engines at their maximum efficiency makes IPS systems more efficient.IPS systems allow easier introduction of new technologies into existing ships. Today’s IPS systems occupy alarger volume and weigh more than most mechanical drive systems.Single vs. twin shaft – Both single and twin shaft arrangements are considered in the machinery trade-off. Theimportant benefits of having a single shaft are that it is lighter and costs less. The disadvantages of a single shaftare that there is no redundancy, less maneuverability, larger risk of total propulsion loss, and increasedvulnerability. The benefits of having two shafts are redundancy, increased maneuverability and survivability. Thedisadvantages to having two shafts are the need for more maintenance and increased cost, weight and volume.Propulsion Engine Alternatives - Three propulsion engines were chosen for trade-off in CUVX. The Colt-Pielstick 2.5V16 medium speed diesel engine was selected from medium speed diesels listed in Table 9 because ofits commonality with LPD-17. The advantages of using a medium speed diesel engine are its inherent reliability,fuel efficiency, and low cost. Disadvantages are its high weight and volume, and low power density relative to gasturbine engines. Two gas turbine engines were selected for trade-off in CUVX, the LM-2500 and WR-21 ICR.LM-2500 is the US Navy’s standard gas turbine engine with good power range and high power density. Thedisadvantage of this engine is that it has high fuel consumption, particularly at part loads. The WR-21 ICR has