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Propulsion Introduction Force, Energy & Power Thermodynamics What makes ships go? Force Energy Power FORCE Units: Pounds (lbs) Tons (1 Ton = 2000 lbs) Newtons (1 N = 0.225 lbs, 1 lb = 4.45 N) Examples: Thrust Force: produced by propeller to drive ship) Resistance Force: determined by hull shape & vessel speed—opposes thrust FORCE RES THR THRUST = RESIST (equilibrium) Ship proceeds at a constant speed Velocity = distance / time o 1 knot = 1 nautical mile / hour o 1 naut mi. = 6076 ft o 1 statute mi. = 5280 ft FORCE THRUST > RESIST Ship accelerates Resistance increases with speed o Until Resistance = Thrust o Ship at new, faster speed FORCE RESIST > THRUST Ship decelerates Resistance decreases with speed o Until Resistance = Thrust o Ship at new, slower speed What makes ships go? Force Energy Power Propeller as a Pump Moves a quantity of water (GPM) And raises pressure (psi) Propeller Horsepower = GPM x PSI 1714 Gal (231 cu.in.) x lbs = force x distance min (60 sec) sq.in time Press Difference (DP) x Propeller Area = THRUST Efficiency Losses PWR in Process PWR out or System Efficiency Nothing is 100% efficient! Efficiency Delivered Horsepower (DHP)= energy per unit time delivered to the propeller DHP EHP Losses Stern Tube Propulsive Efficiency = EHP DHP (30% or more) Efficiency Shaft Horsepower (SHP)= energy per unit time delivered to the tailshaft SHP DHP EHP Losses Line shaft Stern Tube (30% or more) Tailshaft Losses (< 1%) Efficiency Heat for Auxiliaries & Losses BTU/min to engine BTU’s Released: HHV x Fuel Rate FUEL DHP BHP SHP Engine Transmission & Shafting Brake Horsepower (BHP)= engine output delivered to drive train (line shaft losses: 2-5%) ENGINE converts Thermal Energy to Mechanical Energy (efficiencies < 50%) Thermal Energy produced by the combustion of fuel EHP Propulsion Plants BTU/min to engine BHP FUEL Engine Transmission & Shafting Many Energy Conversion (thermal Mechanical) Alternatives including … STEAM (conventional or nuclear), DIESEL (slow speed or medium speed), and GAS TURBINE Steam Propulsion STEAM REDUCTION GEAR BOILER or REACTOR TURBINES WATER Advantages: Conventional plants can burn very low grade fuel Nuclear plants can go years without refueling Good efficiency over a wide range of speeds Disadvantages Large Space requirements Long start-up time Difficult to completely automate (large crew sizes) High initial (capital) costs (Slow Speed) Diesel Propulsion Advantages: Simple to automate (“unmanned” engine room & Bridge Control) Can burn low grade fuel Relatively short start-up time Disadvantages Low efficiency at low speed Restricted maneuverability Many parts—failure of one causes downtime (Medium Speed) Diesel Propulsion G G G G M G Advantages: Flexible engine arrangements Suitable for electric drive Short start-up time Disadvantages Burns higher grade fuel Multiple engines required for high hp ships Significant maintenance burden Gas Turbine Propulsion Gas Generator (jet engine) Power Turbine Advantages: Short start-up time Engines (Gas Generators) changed out for regular maintenance Reduction/ reversing Gear Gas Turbine Propulsion G M G G M Advantages: Disadvantages High grade (jet) fuel Short start-up time Engines (Gas Generators) changed out Non-reversing—requires auxiliary gear for astern for regular maintenance operation Suitable for electric drive