Propulsion Introduction Force, Energy & Power Thermodynamics

What makes ships go? Energy Force Power

FORCE : Units: Pounds (lbs) Tons (1 Ton = 2000 lbs) lbs, 1 lb = 4.45 N) Newtons (1 N = 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 Ship proceeds at a constant speed Velocity = distance / time Velocity = distance / time o1 = 1 nautical mile / hour o1 knot = 1 nautical mile / hour o1 naut mi. = 6090 ft = 1.15 statute mi. RES THR

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

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

RESISTANCE = K x V 2 K is a function of hull shape & condition Doubling velocity requires 4 times the thrust Doubling velocity requires 4 times the thrust oat 5 kt  T = 25K oat 10kt  T = 100K at 20 kt  T = 400K at 20 kt  T = 400K o(16 times the thrust at 5 kt)

RESISTANCE = K x V 2 Each increasing knot requires more thrust than the previous 1- knot increase Each increasing knot requires more thrust than the previous 1- knot increase o From 5 to 10 kt required an increase of 75K o From 15 (225K) to 20 (400K) is an increase of 175K tons of thrust

What makes ships go? Energy Force Power

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 V 2, ship speed significant in energy (fuel) costs

ENERGY in many forms Mechanical Energy (“work”): Force x Distance (lb-ft; Ton-mi; N-m; etc.) Thermal Energy (“heat”): 1 BTU will raise 1 lb of H 2 O 1 o F 1 BTU equivalent 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)

What makes ships go? Energy Force Power

POWER Rate of 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 = kW = BTU/sec = 2545 BTU / Hr Force x Distance / Time = Force x Velocity Thrust x Velocity = K x V 2 x V = K x V 3 =Ship’s Effective Horsepower (EHP) EHP proportional to speed cubed!

EHP = THRUST x VELOCITY At any constant speed At any constant speed Thrust = Resistance = K x V 2 Thrust = Resistance = K x V 2 So Thrust x Velocity = So Thrust x Velocity = K x V 2 x V = K x V 3 (Doubling V requires 8 x HP!) EHP(10) = K x 1000 EHP(10) = K x 1000 EHP(20) = K x 8000 EHP(20) = K x 8000 “K” for TSES VI is ≈ 2 “K” for TSES VI is ≈ 2 X 8 X 2

EHP = THRUST x VELOCITY So EHP = K x V 3 So EHP = K x V 3 & Doubling V requires 8 x HP EHP(10) = K x 1000 EHP(10) = K x 1000 EHP(20) = K x 8000 EHP(20) = K x  11 kt: 10  11 kt: 331xK increase in HP 19  20 kt: 19  20 kt: 1141xK increase HP

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

Propeller as a Pump Propeller Horsepower = GPM x PSI Propeller Horsepower = GPM x PSI Gal (231 cu.in.) x lbs = force x distance min (60 sec) sq.in time min (60 sec) sq.in time Press Difference (  P) x Propeller Area = THRUST Press Difference (  P) x Propeller Area = THRUST Moves a quantity of water (GPM) Moves a quantity of water (GPM) And raises pressure (psi) And raises pressure (psi)

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

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

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

Efficiency FUEL BTU’s Released: HHV x Fuel Rate BTU/min to engine Engine Transmission & Shafting SHP DHP EHP Brake Horsepower (BHP)= engine output delivered to drive train (line shaft losses: 2-5%) Brake Horsepower (BHP)= engine output delivered to drive train (line shaft losses: 2-5%) ENGINE converts Thermal Energy to Mechanical Energy (efficiencies < 50%) ENGINE converts Thermal Energy to Mechanical Energy (efficiencies < 50%) Thermal Energy produced by the combustion of fuel Thermal Energy produced by the combustion of fuel Heat for Auxiliaries & Losses BHP

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

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

(Slow Speed) Diesel Propulsion Advantages: Simple to automate (“unmanned” engine room & Bridge Control) Simple to automate (“unmanned” engine room & Bridge Control) Can burn low grade fuel Can burn low grade fuel Relatively short start-up time Relatively short start-up time Disadvantages Low efficiency at low speed Low efficiency at low speed Restricted maneuverability Restricted maneuverability Many parts—failure of one causes downtime Many parts—failure of one causes downtime

(Medium Speed) Diesel Propulsion Advantages: Flexible engine arrangements Flexible engine arrangements Suitable for electric drive Suitable for electric drive Short start-up time Short start-up time Disadvantages Burns higher grade fuel Burns higher grade fuel Multiple engines required for high hp ships Multiple engines required for high hp ships Significant maintenance burden Significant maintenance burden G G G G G M

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

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