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Unit 8
Propulsion Intro
Notes:
What makes ships go?
Force (thrust):
 lbs
 Tons (2000lbs)
 Newtons
(1 lb = 4.45 N)
Distance
 feet (English),
meters (SI)
 1 (statute) mi =
5280 ft
 1 (naut) mi =
6080 ft
(1.15 statute mi)
RESISTANCE
Energy (work)
= Force x Distance
 ft-lbs
 Ton-(naut)mile =
12,160.000 ft-lbs!
 Newton-meter =
joule
Velocity =
Distance/Time
 1 knot =
1 (naut)mi/hour
= 1.15 mph
= .69 ft/sec
Power
= Force x Distance
Time
= Energy/Time or
= Force x Velocity
 1 hp =
550 ft-lbs/sec =
33000 ft-lbs/min
= 746 watts
 1 watt = 1
joule/sec
THRUST
Where:
 Thrust is determined by energy delivered to propeller by
engine, and
 Resistance is determined by ship geometry and ship speed
 Resistance  Velocity2  R = K x V x V
(“K” is determined by the shape and condition of hull)
To push ship at constant speed V (knots),
Thrust (Tons) must = Resistance (Tons)
During speed change
Fnet = Thrust - Resistance = Mass of Ship x acceleration (F=Ma)
 if T>R then ship speeds up,
R increases until R=T (equilibrium at new ship speed)
 if T<R then ship slows down,
R decreases until R=T (equilibrium at new ship speed)
PS 111. Professional Studies
Unit 8: Propulsion Introduction
Remember, since Resistance  Velocity2
Speed Thrust
(knots) KV2
Twice the speed requires 4 times the thrust
1
Kx1
2
Kx4
5 times the speed requires 25X the thrust
3
Kx9
4
Kx16
------------------------------- 9K for a one knot increase
5
Kx25
10
Kx100 ------------------------------15
Kx225
16
Kx256
17
Kx289
18
Kx324
19
Kx361
20
Kx400 ------------------------------- 39K for a one knot increase
-------------------------------
MECHANICAL ENERGY (work): Force x Distance
A given ship develops 100 T of thrust to make 8 knts
If Port A  Port B = 5000 naut mi
Energy expanded in pushing ship = 500,000 T-n.mi.
Puzzle:
Express the above in lb-ft.
If 778 lb-ft is equivalent to 1 BTU, express the above in BTU.
If one Ton of fuel releases 40,000 BTU when combusted,
how many Tons of fuel is required to push the ship from A to
B?
POWER: Rate of production or consumption of energy
Energy = force x distance (lb-ft/sec, ton-mi/hr, etc.)
Time
time
550 lb-ft/sec = 33,000 lb-ft/min = 1 horsepower
1 N-m/sec = 1 joule/sec = 1 watt
1000 joule/sec= 1 kilowatt (kW)
1 hp = 746 watt = 0.746 kW
force x distance = force x velocity (1 ton-knt = 6.14 hp)
time
Effective Horsepower (EHP) = Thrust(T) x Speed (knt) x 6.14
8 -- 2
Notes:
PS 111. Professional Studies
Unit 8: Propulsion Introduction
EHP = rate at which energy is delivered to the hull of the ship
Since Thrust = K V2; EHP = K V2 x V = K V3
Speed
(knots)
1
2
3
4
5
10
15
16
17
18
19
20
EHP
KV3
Kx1
Kx8
Kx27
Kx64
Kx125
Kx1000
Kx3375
Kx4096
Kx4913
Kx5832
Kx6859
Kx8000
Twice the speed requires 8 times the hp
5 times the speed requires 125X the hp
--------------------------- 875K for a one knot increase
---------------------------
--------------------------1141K for a one knot increase
--------------------------
What provides the thrust?
The propeller.
Propeller as a screw:
Pitch = (theoretical) advance per revolution
thus engine mileage
= total revs/day x Pitch (ft) / 6077
slip = Engine Miles – Observed Miles
Engine Miles
Pitch (in feet
or meters)
Ship speed (knots) = pitch x RPM / 6077
and Propeller Horsepower
= Thrust (lbs) x RPM(ave) x Pitch /5252
Propeller as a pump:
Water pulled through propeller leaves at a greater pressure than it
enters
 Since Force = Pressure x Area, higher pressure side of
propeller provides greater force
 Net force (thrust) is the pressure difference x propeller
blade area
 Approximating total blade area as a disc with a 20 ft
pressure differential. Thrust = 2 lbs/in2 x 144 in2/ft2 x 314
ft2 = 90,432 lbs
8 -- 3
Notes:
PS 111. Professional Studies
Unit 8: Propulsion Introduction
Notes:
Prop “Disc” Area:
Ap = R
2
Thrust =
Suction
P1
Disch.
P2
P x Ap
H2O
P =
P2-P1
Pressure = force/unit area
 lbs/sq.in. (PSI)
 N/sq.m.
 Bars = .001 N/sq.m.
 1 atmosphere,
(actually 0.9867 Atm.)
Pumping Power:
= capacity x pressure rise (P)
 GPM x PSI / 1714 (in hp)
 m3/sec x Nt/m2 (in watts)
 m3/sec x bars x 27.8 (in
watts)
What turns the propeller? – the propeller shaft
EFFICIENCY = output (power)
Input (power)
Output = Input – losses
Thus: Eff = _
Pout _ = Pin – losses
Pout + losses
Pin
Effective hp (EHP) – delivered to hull
Developed hp (DHP) – delivered to propeller
Propulsive efficiency = EHP / DHP (approx 30% losses)
Shaft hp (SHP) – power available at end of line shaft
8 -- 4
PS 111. Professional Studies
Unit 8: Propulsion Introduction
 Brake Horsepower (BHP)= engine output delivered to drive
train (line shaft losses: 2-5%)
 some of the torque delivered to the reduction gears by the
engine is used to overcome friction in the drive train; thus
the difference in BHP, SHP and DHP
 BHP-SHP = Line Losses
 numerically, HP = Torque (ft-lbs) x RPM
5252
 ENGINE converts Thermal Energy to Mechanical Energy
(efficiencies < 50%)
 Thermal Energy produced by the combustion of fuel
PROPULSION PLANTS
 Energy Conversion (thermal  Mechanical) systems
Many Alternatives including …
 STEAM (conventional or nuclear)
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
8 -- 5
Notes:
PS 111. Professional Studies
Unit 8: Propulsion Introduction
 DIESEL (slow speed)
Advantages:
• Simple to automate
(“unmanned” engine room
& Bridge Control)
• Can burn low grade fuel
• Relatively short start-up
time
Notes:
Disadvantages
• Low efficiency at low speed
• Restricted maneuverability
• Many parts—failure of one
causes downtime
 DIESEL (medium speed – direct drive)
 DIESEL (medium speed – electric drive)
8 -- 6
PS 111. Professional Studies
Medium Speed Diesels:
Advantages:
• Flexible engine
arrangements
• Suitable for electric drive
• Short start-up time
Unit 8: Propulsion Introduction
Notes:
Disadvantages
• Burns higher grade fuel
• Multiple engines required
for high hp ships
• Significant maintenance
burden
 GAS TURBINE (direct drive)
 GAS TURBINE (direct drive)
Gas Turbines:
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
Visit:
http://www.designnews.com/article/CA212211.html?ref=nbra
http://www.fas.org/sgp/crs/weapons/RL33360.pdf
http://www.amsuper.com/products/library/Maritime_Reporter_final3_sk1_73002
_final.pdf
8 -- 7
PS 111. Professional Studies
Unit 8: Propulsion Introduction
THERMODYNAMICS
Notes:
Branch of science dealing with the interchange of thermal &
mechanical energy
1st Law: Conservation of Energy


2 LAWS
non flow systems:
Net Heat[in] = Net Work[out] + Internal Energy[change]
steady-flow systems:
Flow-energy[in] + Heat[in] =
Flow-energy[out] + Work[out]
where Flow-energy = enthalpy
2nd Law: Not all processes are reversible

6
PROPERTIES
3 PHASES

Work{in}--->Heat[out]
BUT Heat[in]--->Work[out] + Heat[out]
order--->randomness (as measured by entropy )






Temperature (T, degrees F,C, R or K)
Pressure (P, lbs/in2, PSI “absolute” or “gage”)
Internal Energy (u, BTU/lbm)
Specific Volume (v, ft3/lbm, reciprocal of “density’)
Enthalpy (h, BTU/lbm, “total heat content”)
Entropy (s, BTU/lbm. measure of “irreversibility”)

(sometimes quality is considered a 7th)



Solid
Liquid
Vapor (Gas)
note: a fluid can be either a liquid or a vapor
3 MODES
of HEAT
TRANSFER
2 EFFECTS of
HEAT
TRANSFER



Conduction (typically through solids)
Convection (via motion of fluids)
Radiation (via E-M waves, “line of sight”)


Sensible Heat (changes temperature)
Latent Heat (changes Phase)
Visit:
http://www.jcphysics.com/toolbox_indiv.php?sub_id=22
http://en.wikipedia.org/wiki/Thermodynamic_properties
8 -- 8
PS 111. Professional Studies
Unit 8: Propulsion Introduction
Temperature is an indication of the internal energy contained in a
substance
 Relative scales: Fahrenheit (oF) and Celsius (oC)
where C x 9 = (F - 32) x 5
 Absolute scales: Rankine (oR) and Kelvin (oK)
where R = F + 459.7 and K = C + 273.2
o
o
o
C
F
R
K
Gold melts
1336.15
1063.00
1945.40
2405.07
Silver melts
1233.95
960.80
1761.44
2221.11
Water Boils @ 600 psig
(TSES IV Boilers)
763.15
490.00
914.00
1373.67
Water Boils @ 1 Atm (14.7psia)
373.15
100.00
212.00
671.67
"Room Temperature"
295.15
22.00
71.60
531.27
Water Freezes (@ 1 Atm)
273.15
0.00
32.00
491.67
90.18
-182.97
-297.35
162.32
0.00
-273.15
-459.67
0
Oxygen Boils
Absolute Zero
Pressure = Force / unit area
:examples  pounds / sq.in 
Atm
103.04
82.63
41.82
35.01
28.21
21.41
14.61
11.20
4.40
2.04
1.00
0.68
0.34
0.07
0.00



Bars
104.41
83.73
42.37
35.48
28.59
21.69
14.80
11.35
4.46
2.07
1.01
0.69
0.34
0.07
0.00
PSIA
1514.7
1214.7
614.7
514.7
414.7
314.7
214.7
164.7
64.7
30
14.7
10
5
1
0
PSIG
1500
1200
600
500
400
300
200
150
50
15.3
0
-4.7
-9.7
-13.7
-14.7
tons / sq.ft

newtons / sq.m
Kg/sq.cm. KPascal
106.47
85.38
43.21
36.18
29.15
22.12
15.09
11.58
4.55
2.11
1.0333
0.70
0.35
0.07
0.00
10434
8368
4234
3546
2857
2168
1479
1135
446
207
101
69
34
7
0
in. Hg
(ABS)
3083.0
2472.4
1251.1
1047.6
844.1
640.5
437.0
335.2
131.7
61.1
29.92
20.4
10.2
2.0
0
in. Hg
(VAC)
0
9.6
19.7
27.9
29.92
absolute pressure is measured relative to a perfect vacuum
gage pressure is measured relative to atmospheric pressure
Kg/sq.cm is actually mass/unit area, but 1 kg “weighs” 9.8 Nt
(on Earth)
8 -- 9
Notes:
PS 111. Professional Studies

Unit 8: Propulsion Introduction
pressure may be interpreted as the height of a column of
liquid it can support (i.e. 1 atmosphere of pressure can
support 29.92 in.or 760mm of Hg, 33.9 ft or 10.3 m of H2O)
Vacuum measure
Perfect Vacuum
Atmospheric
Pressure
29.92
“Hg A Barometer is used to measure
atmospheric pressure via
comparison to a (very nearly)
perfect vacuum
0 psia
29.92 “Hg
(0 psia)
20.0 “Hg
14.7 psia
Evacuated
Space
(5 psia)
Atmospheric
Pressure
10.0 “Hg
(10 psia)
0.0 “Hg
(14.7 psia)
A Vacuum Gage is used to
measure the pressure in an
evacuated space via
comparison to atmospheric
pressure
EFFECTS OF HEAT TRANSFER
When heat is transferred to/from a substance, one of two effects
may be realized
 Temperature change– a rise or fall in temperature is a
sensible heat effect
 Phase change– (liquid-vapor, vapor-liquid, solid-liquid,
liquid-solid) is a latent heat effect
 But not both simultaneously
A pot of boiling water is 212oF (at standard atmospheric pressure)
whether it is simmering or at a rolling boil – the rate of
vaporization is dependent on the rate at which the latent heat is
absorbed, not the temperature
8 -- 10
Notes:
PS 111. Professional Studies
Unit 8: Propulsion Introduction
 Consider one pound of H2O at atmospheric pressure:
Notes:
TEMP
Condensing
Boiling
212oF
Superheated
steam
Liquid/vapor mix
“wet steam”
Solid/
liquid
mix
Saturated
liquid
Melting
Saturated
vapor
Freezing
32oF
0 oF
Sensible
HEAT (BTU)
144 180 BTU
BTU Sensible
Latent
Sensible
970 BTU
Latent
At other than atmospheric pressure, the processes are the same,
but the values (freezing temp, boiling temp, latent heat of
vaporization, etc.) are different
 At pressures below atmospheric (vacuum) water boils at
less than 212oF
 At pressures above atmospheric, water boils at
temperatures greater than 212oF
Pressures
ABS
.75 psia / 1.5”Hg
5 psia / 9.9”Hg
10 psia / 19.9” Hg
14.7 psia / 1 Atm
29.7 psia
164.7 psia
614.7 psia
1214 psia
REL
28.5” Hg
20” Hg
10” Hg
0” Hg / 0 psig
15 psig
150 psig
600 psig
1200 psig
SAT
TEMP
92oF
162oF
193oF
212oF
250oF
361oF
490oF
570oF
LATENT HEAT of
vaporization, hfg
1040 BTU / lb
1001 BTU / lb
982 BTU / lb
970 BTU / lb
945 BTU / lb
861 BTU / lb
728 BTU / lb
610 BTU / lb
More precise values and other thermodynamic properties are
found in Steam Tables
8 -- 11
PS 111. Professional Studies
Unit 8: Propulsion Introduction
THERMODYANMIC CYCLES:
Utilize a continuous exchange of mechanical and thermal energy
 A thermodynamic cycle has 5 components;
o A working fluid to transport energy through the cycle
o A heat source to deliver thermal energy to the working
fluid
o A heat sink to retrieve thermal energy from the working
fluid
o An engine where thermal energy is converted into
mechanical (work) energy)
o A pump to circulate the working fluid
 Cycles may be open or closed
Closed cycle
WORKING
FLUID
ENGINE
W
HEAT
SINK
HEAT
SOURCE
PUMP
H
H
W
The Steam Cycle, refrigeration and air conditioning cycles are
examples of closed cycles
Open Cycle
W
W
PUMP
HEAT
SOURCE
WORKING
FLUID
ENGINE
H
HEAT
SINK
H
Diesel engines, gasoline engines, and gas turbines are
examples of open cycles
8 -- 12
Notes: