Theory 2 Flashcards
use of a gear box?
Transmits power from the prime mover to the shaft
Allows variations in speed and power
allows changes between ahead and astern thrust
main components of a gearbox?
primary wheel
secondary wheel
primary pinon
secondary pinon
quill shaft
casing
bearings
Driving and driven gear names?
pinion = driving
wheel = driven
how do you change the direction of the gears?
add a second gear
how do you change the speed of a gear?
make the driving gear smaller with less teeth
Name the gears and reductions?
straight spur
helical
double helical
worm wheel
single reductions
double reduction
dual tandem
what is a straight spur?
teeth mesh as they are parallel
low speed applications where noise is not a problem
what is a helical gear?
angle cut teeth
thrust bearings to stop it from thrusting
high speed application as noise needs to be minimal
what is a double helical gear?
cancel out thrust due to the opposite angle cuts, so bearings not required.
can be interchanged with straight spur gears
what is a worm wheel?
pinion 90 degree angle to wheel
worm resembles a screw and is always the driving gear.
if power is lost, it will self lock
what is single gear reduction?
meshing a larger wheel with a smaller pinion
affects output speed
limit 15:1
what is dual tandem?
2 reductions in 1
has a quil shaft
loading is halved so smaller pinions can be used.
what does quill shaft do?
maintain alignments of the loading
acts as a torsional spring
handles torque more than single shaft
name the gearbox ancillaries
shaft brakes
thrust block
turning gear
Purpose of a shaft brake?
stops and holds propeller shaft
it has a brake disc attached to a shaft and 3 evenly spaced brake callipers (2 brake pads in each)
check all brakes are applied and staionary
check opposite afterwards
purpose of a thrust block?
large thrust bearing at gearbox end of propeller shaft
absorbs force of the propeller so that ship moves as a whole
machined collar on both sides of which are fitted white metal pads lubricated by micelle oil wedge principle
turning gear purpose ?
slowly rotate the shaft and propeller in a controlled manner for docking and maintenance
on top of gear case and provides drive onto the upper quill shaft in the gearbox
worm wheel
- goes wrong way, it will lock up
- power lost, it will lock up
what is forced lubriction?
provides lubrication to all gearing and bearings
gearing pump only works when gearbox is turning
motor driven pump primes gearbox lub oil system and used to drain the oil acta as back up
closed loop system
what is a serkat?
allows hot oil to pass though the cooler and cool oil to bypass the cooler
controls oil temp
what is a turning valve?
provides boundary lubrication by directing high pressure oil to components that need it
what are cut ins?
if oil pressure drops below 18.5 PSI, the pressure switch will signal the MD pump to take over
checked every 24 hours
hazards of gearboxes?
noise
heat/fire
moving parts
overalls correct and man below tally followed
name the sections of the shaft
thrust
intermediate
tail
what does a plumber block do?
supports the weight of the shaft, doesn’t absorb thrust
dynamic lubrication
made up of bearings, casing, dipstick, journal pads and oil cooler
what does a bulkhead gland do?
keeps water tightness between compartments.
white metal lined bearing
lubricated with grease.
purpose of stern seal?
to keep watertight integrity where the shaft exits the ship via the hull.
has an emergency inflatable seal, only prevents water tightness when shaft is stationary
name underwater shaft line components and describe their purpose
main and intermediate A brackets
supports weight of propeller shaft, lubricated by sea water.
what is SKF coupling?
hydraulic coupling, allows the tail and intermediate sections of the shaft to be split without leaving flange through the seals.
inner and outer sleeve, very tight.
name 2 types of propeller
fixed blade and controlled pitch propeller
what order does the shaft line components go in?
THRUST
gear box
thrust block
plumber block
INTERMEADIATE
blukhead Gland
Plummer block
stern seal
intermediate A bracket
TAIL SKF coupling
main A bracket
proeller
what does a gas turbine do?
converts heat energy into rotary motion for ship propultion
what type of gas turbines does each ship have and how many?
type 23= SPEY
type 45= WR21
both have 2
what does IEP stand for?
integrated electrical propulsion
what does CODLAG stand for?
Combination of diesel and electric and gas
advantages of gas turbines
ability to get underway quickly
ease of operation with emphasis on remote control
high power/weight ratio
minimum shipboard maintenance
low manpower
what are the 5 strokes of a gas turbine?
inductions
compression
combustion
power
exhaust
what is induction?
air from previous stage goes in
what is compression?
air goes in at atmospheric pressure into LP compressor
increases the pressure using a series of rotating blades
have divergent passages within them that moves and compresses air as it passes between the blades.
the air goes out into a second set of rotating blades, HP compressor
the pressure and temperature both increase.
what is combustion?
releases maximum amount of chemical energy from the fuel
mixes compresses air with atomised fuel
ignitor is housed here and provides a high tension spark to ignite mixture
some of air is used to cool the chamber and burnt when there is a flame
air heated up and dramatically before becoming the working fluid for turbines.
explain what air goes where in the combustion chamber
15% primary air- this air is used to help ignite the burner
10% secondary air- there creates a safety layer between the edge of the can and the flame
75% tertiary air- becomes working fluid
what is the power stroke?
remaining energy after passing HP and low LP goes through the power turnbine.
what is exhaust?
gases directed away via tunnel
what is the routine maintnace?
prestart check as per book of reference
done hourly
- pressure and temp
- oil levels
-noise + vibration
- leaks
always inform senior rate
what is wet motoring?
fuel being supplied to the engine with igniters and fuses isolated
happens after any maintaince to purge it
what is dry motoring?
fuel, fuses and igniters are isolated
purges combustion chamber of nay unburnt fuel and any explosive gases after a fail start.
what is water washing?
carried out to prevent debris falling in compressor blades.
used with distilled water and compressor cleaning inhibited fluid
what is inhibiting fluid?
PX24 apply after 10 days of the engine being off, spray down the blades
prevents corrision
what does the and trip do?
activates HP fuel shut off cock
if engines are online the command approval must be met before operating this trip
what do fire detectors do?
provide indecation of high temperature on LCP and SCC
what is the power turbines entry temperature? (PTET)
governor - monitors PTET and controls the amount of fuel to the engine if these set levels are exceeded
trip- stops the engine should the exhaust gas temperature exceed safety parameters
what does the partial overspeed safety device do?
if engine overspeed, reduces the fuel supplied to reduce engines speed
what does vibration monitor do?
monitors engine vibrations levels and sets off an alarm if it exceeds
what does power turbine overspeed do?
if the turbine speed reaches 110% of its safe limit, high pressure shut off cock will stop the engine by isolating fuel supply
exmaples of safety inter-locks
electrical supplies
clutch being disengaged
what are igniters?
produce powerful sparks using voltages
like spark plugs in a petrol engine
what is a drenching system?
when the fire alarm goes off, CO2/BTM is realised.
the ventilation system is shut down, flaps closed.
ventilate after use
what is the module ventilation?
the module that house the gas turbine. it cools the system via ventilation system
air goes in due to the low pressure (depression) created at the other end of the tunnel.
air circulates the system keeping it cool
depression is formed by rushing of exhaust gasses.
stages of the gas turbine? before 5 stroke parts.
3 stage filtration
intake trunking
splitter/silencer
stone guard
transition duct
cascade bend
engine intake flare
explain the 3 part filtration system?
- spray eliminator- air changes direction to to baffle plates, this means that the water drops off allowing mainly dry air to pass
- knit mesh filter- removes any derbies
- water eliminator- removes any residual water
what is a splitter/ silencer?
perforated valves with sound absorbing materials
air goes over the vanes and splits the air flow
removes turbulence, air noise and buffering
what is a stoneguard?
prevents large particles of debris from entering the turbine
what is the transition duct?
provides a smooth change from square cross section to a circular cross section
what is the cascade bend?
allows for a smooth 90 degrees change of direction
what is the engine intake flare?
seals the engine intake from rest if the module
houses water wash ring
has hoes which allow water/compressor cleaning fluid
sprays water when it needs to be cleaned.
name the ways to embark fuel at sea
RAS
Road bowser
direct jetty pipeline
jetty storage tank
barge
what is RAS?
fuel taken from a supply ship.
everyone wears anit-flash
very hazardous because ships are clsoe
what is road bowser/tank?
receive from a road bowser
taken in at a slower rate so takes longer but is safer
how does a filling trunk work?
fuel enters and fills up until it reaches the weir height
continued fuelling will cause it to to cascade over the weir and down into the fuelling manifold
what is a displaced tank?
fuel tank that contains some water
only over filled to 90% to keep ship stability
What is an non-displaced tank?
fuel tank that only holds fuel then passes through the centrifuge
what is the centrifuge?
separates oil/fuel from water using centrifugal force. once clean, stored in the service tank
what is fuel tested for?
water
dirt
surfactants
reasons to test fuel?
salt can cause corrosion
water can cause MBG
dirt will block fliters
types of fuel test?
visual
water reaction test
diesel filteration test
colour test
hazards of fuel?
fire
toxicity
dermatitis
pollution
flow of fuel from tanker to engine?
tanker
filling trunk
manifold
displaced tanks
centrifuge
non-displaced tanks
fuel transfer
service tanks
fuel boost pump
fuel boost ringmain
