0310000 JOHNSON HOUSING,Impeller

Rating Definitions
The Caterpillar marine propulsion engine rating definitions is:*AFor use with little load cycling in oceangoing displacement hulls such as freighters, tugboats and bottom-drag trawlers, and deep river towboats.*BFor use in midwater trawlers, purse seiners, crew and supply boats, ferry boats with trips longer than one hour, and towboats in rivers where locks, sandbars, curves, or traffic dictate frequent slowing.*C For use in yachts with displacement hulls, as well as ferries with trips less than one hour, fish boats moving at higher speeds out and back (e.g., lobster, crayfish and tuna), and short trip coastal freighters.*D For use in pleasure craft and yachts with displacement hulls, as well as patrol, customs, police and fire boats. Also for bow/stern thrusters.*EFor use in pleasure craft with planing hulls, as well as for pilot, harbor patrol and harbor master boats. Some fish boats operate on duty cycles where D or E engine ratings apply.Time at full throttle is the cumulative time the engine is operated at full throttle load and speed during a work cycle, duty cycle, or voyage.The rating for an application is based on a load profile determined by time at various throttle settings or engine speeds. In general, an application requiring less time at full throttle, or lower engine rpm at reduced throttle operation, can utilize a higher rating.As a general guideline, typical reduced engine speeds for each rating level are summarized in the following chart: Fuel consumption at the suggested reduced rpm is at or near the engine's optimum fuel efficiency.The above rating definitions assure the customer obtains an acceptable and competitively priced match between initial cost and total life and lifetime costs.When operating the engine in an application consistently requiring more time at full throttle than the designated level, higher maintenance costs and premature wear of the engine will be encountered.Application Guidelines
In selecting a rating for a specific application, the most important consideration is time spent at full throttle. Additionally these rating definitions identify percent of time at full throttle and corresponding times below rated rpm. This rpm reduction lowers kW (horsepower) requirements as propeller demand follows a cubic speed/power curve.For example, an engine operating at 90% of rated speed would be loaded by a typical propeller to about 73% of rated power. Operating at recommended reduced speed controls the engine load at or below the continuous power level.Engine Service Life
Expected engine life (time to overhaul) can be expressed in terms of service, clock hours, years of operation or liters (gallons) of fuel consumed.Expected engine life can generally be predicted by the average power demanded of the engine over a period of time. Reduced hours of operation at full throttle and/or operating at reduced throttle settings result in lower average power demand and should increase the length of operating time before an engine overhaul is required.Application of marine engine ratings using the new, recommended, application guidelines will provide acceptable engine life.For most applications, the customer can provide profile information from similar vessels or the actual vessel, if repowering. If such information does not sufficiently indicate the operating profile, instruments are available to more precisely define engine operation.A recording tachograph (7D1513), available commercially and from Caterpillar parts departments, can establish an operating profile. It records engine speeds versus time on a paper chart.