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 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

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

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

What makes ships go? Force Energy Power

Gal (231 cu.in.) x lbs = force x distance 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 Nothing is 100% efficient! PWR in PWR out Losses Process or System Efficiency Nothing is 100% efficient!

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

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

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

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

Steam Propulsion BOILER REDUCTION GEAR or REACTOR TURBINES STEAM 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 M 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 Reduction/ reversing Gear Advantages: Short start-up time Engines (Gas Generators) changed out for regular maintenance

Gas Turbine Propulsion M M 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