Propulsion Introduction

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. = 6090 ft = 1.15 statute mi.

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. RESISTANCE = K x V2 K is a function of hull shape & condition • Doubling velocity requires 4 times the thrust • at 5 kt  T = 25K • at 10kt  T = 100K • at 20 kt  T = 400K • (16 times the thrust at 5 kt)

8. RESISTANCE = K x V2 • Each increasing knot requires more thrust than the previous 1-knot increase • From 5 to 10 kt required an increase of 75K • From 15 (225K) to 20 (400K) is an increase of 175K tons of thrust

9. What makes ships go? Force Energy Power

10. ENERGY (mechanical) Force x Distance Units: • Pounds x Feet (lb-ft) • Newtons x meters (1 N-m = 1 joule) • Other: Tons-miles; oz-inches; etc. Examples: • Thrust x Distance (port A to port B) • Since Thrust = K x V2, ship speed significant in energy (fuel) costs

11. ENERGY in many forms Mechanical Energy (“work”): • Force x Distance (lb-ft; Ton-mi; N-m; etc.) Thermal Energy (“heat”): • 1 BTUwill raise 1 lb of H2O 1oF • 1 BTUequivalent to 778 lb-ft of mechanical “work” • The amount of heat released in the combustion of 1 lb of fuel (BTU/lb) is the Higher Heating Value (HHV) of the fuel Electrical Energy (“kW-Hrs”): • One 60-watt (0.06 kW) bulb burning for 24 hrs consumes 1.44 Kw-Hrs of energy (at 15 cents per Kw-Hr, a 60 watt bulb burning for a month costs 0.06 x 24 x 30 x $0.11 = $4.75)

12. What makes ships go? Force Energy Power

13. POWER Rateof Energy Production or consumption Force x Distance / Time: • lb-ft/min; Ton-mi/hr; N-m/sec (=joule/sec = watt) • 550 lb-ft/sec = 33,000 lb-ft/min = 1 horsepower • 1 horsepower = 746 watts = 0.746 kW = 0.707 BTU/sec = 2545 BTU / Hr Force x Distance / Time = Force x Velocity • Thrust x Velocity = K x V2x V = K x V3 =Ship’s Effective Horsepower (EHP) • EHP proportional to speed cubed!

14. X 8 X 2 EHP = THRUST x VELOCITY • At any constant speed Thrust = Resistance = K x V2 • So Thrust x Velocity = K x V2 x V = K x V3 (Doubling V requires 8 x HP!) • EHP(10) = K x 1000 • EHP(20) = K x 8000 • “K” for TSES VI is ≈ 2

15. EHP = THRUST x VELOCITY • So EHP = K x V3 & Doubling V requires 8 x HP • EHP(10) = K x 1000 • EHP(20) = K x 8000 • 1011 kt: 331xK increase in HP • 1920 kt: 1141xK increase HP

16. PITCH (ft or m) Propeller as a Screw • PITCH = theoretical advance of propeller in 1 revolution • PITCH x Total Revs in 1 day = ENGINE MILAGE • Slip = Eng mi – Obs mi Eng mi • Pitch x RPM x 60 min/hr = ship speed (knots) 6077 ft/n.mi

17. 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

18. Losses PWR in PWR out Efficiency Process or System Efficiency Eff = Pout Pin = Pout Pout + Losses = Pin - Losses Pin Nothing is 100% efficient!

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

20. 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%)

21. 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

22. 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

23. 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

24. (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

25. 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

26. 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

27. 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