Transcript U08_Prop1-Intro_v2 - Port Fest Baltimore 2015

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