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Propulsion Introduction

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)

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Propulsion Introduction

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  1. Propulsion Introduction Force, Energy & Power Thermodynamics

  2. What makes ships go? Force Energy Power

  3. 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

  4. THR RES FORCE THRUST = RESIST (equilibrium) • Ship proceeds at a constant speed • Velocity = distance / time • 1 knot = 1 nautical mile / hour • 1 naut mi. = 6076 ft • 1 statute mi. = 5280 ft

  5. FORCE THRUST > RESIST • Ship accelerates • Resistance increases with speed • Until Resistance = Thrust • Ship at new, faster speed

  6. FORCE RESIST > THRUST • Ship decelerates • Resistance decreases with speed • Until Resistance = Thrust • Ship at new, slower speed

  7. What makes ships go? Force Energy Power

  8. 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

  9. Losses PWR in PWR out Efficiency Process or System Efficiency Nothing is 100% efficient!

  10. Losses DHP EHP Efficiency • Delivered Horsepower (DHP)= energy per unit time delivered to the propeller (30% or more) Stern Tube • Propulsive Efficiency = EHP DHP

  11. Losses DHP EHP SHP Efficiency • Shaft Horsepower (SHP)= energy per unit time delivered to the tailshaft (30% or more) Line shaft Stern Tube Tailshaft Losses (< 1%)

  12. DHP SHP BHP Engine Transmission & Shafting EHP Efficiency Heat for Auxiliaries & Losses • 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 BTU/min to engine BTU’s Released: HHV x Fuel Rate FUEL

  13. BHP Engine Transmission & Shafting Propulsion Plants • Many Energy Conversion (thermal  Mechanical) Alternatives including … • STEAM(conventional or nuclear),DIESEL(slow speed or medium speed), and GAS TURBINE BTU/min to engine FUEL

  14. Steam Propulsion STEAM Advantages: • Conventional plants can burn very low grade fuel • Nuclear plants can go years without refueling • Good efficiency over a wide range of speeds REDUCTION GEAR BOILER or REACTOR TURBINES WATER Disadvantages • Large Space requirements • Long start-up time • Difficult to completely automate (large crew sizes) • High initial (capital) costs

  15. (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

  16. G G G G G M (Medium Speed) Diesel Propulsion 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

  17. Gas Turbine Propulsion Advantages: • Short start-up time • Engines (Gas Generators) changed out for regular maintenance Gas Generator (jet engine) Reduction/ reversing Gear Power Turbine

  18. G G M M G Gas Turbine Propulsion Advantages: • Short start-up time • Engines (Gas Generators) changed out for regular maintenance • Suitable for electric drive Disadvantages • High grade (jet) fuel • Non-reversing—requires auxiliary gear for astern operation

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