Requirements of Ship Design
To serve its purpose – trading, offshore exploration/production/support, fishing, towing,
dredging, research, firefighting, icebreakers, etc
Sufficient strength(Depends on design), stable, maintainable, economical to build & operate
Maneuverability, sufficient power to deliver appropriate speed
Self-sustaining (carry enough fuel, food, fresh water & components with high reliability)
Safetyminimize
chance of damage from fire, storm, collision/grounding
Basic Definitions
Classification society: independent org providing guidance & certifications in designing,
building & maintaining(hull, machinery, equipment)
Port(left), Starboard(right), bow/forward(front), stern/aft(back)
Decks(Main:Primary deck, Bridge:deck which navigation equipments are housed, Lifeboat)
Shell: watertight plating around sides & bottom, Superstructure: anything above main deck –
generally referring to accomodation area, Bulkheads: partition within the hull of the ship
Units of measurement
Length: 1 feet = 0.3048m, 1 nautical miles = 1852m/1.15miles/6080ft
Speed: 1 knot = 1 nautical mile/hour = 0.514 m/s
Weight: 1 tonne = 1000kg, Volume: 1 tonne = 1000 cubic feet
Water Density
Density = mass/volume (kg/m3), Specific gravity=density of a substance/density of water (no
unit)
ρ(fw)=1ton/m3=1000kg/m3 (specific gravity of water=1) , ρ(sw)=1.025ton/m3=1025kg/m3
Water(nearly incompressible)ρ doesn’t vary with depth. Density ↑ when salinity ↓ & temp
↑
Tonnage
Volume: Gross tonnage(GT/GRT): total vol. of ship, Net tonnage(NT/NRT): vol. of revenue
earning spaces (i.e. cargo spaces) – GT and NT are measured in tons (1 ton = 1000 cubic feet)
Weight: Deadweight tonnage(DWT): how much mass a ship can safety carry(incl. cargo, fuel,
ballast, stores, crews, etc), Lightweight: weight of ship without any cargo, water, fuel, etc (scrapyard
based on lightweight, only interested in weight of steel) – all measured in tonnes
Displacement: Archimedes Principle: Displacement weight of ship = weight of water displaced by
ship
Ship dimensions
, LOA: Max. length of hull from forward-most point on bow to end of stern(rudder not
included)
LWL: Length of designed waterline (above is freeboard, below is draft)
LBP: Forward p.(FP) is forward end of designed WL, aft p.(AP) is centre of rudder stock
Draft(T): vertical distance from deck to waterline
Air draft: vert. distance from waterline to highest point of ship
Depth(D): vertical distance from deck to keel
Centre of buoyancy (B): CG of the displaced vol. of water.
Centre of gravity (G): line of action of CG and CB must be along the same line when ship is
still
Waterplane area: the section through the hull taken at it’s intersection with water
Lecture 2: Properties of Marine Fuel
Marine Fuels
Crude Oil - Composition by weight(%):
C: 83 - 87, H: 10 - 14, N: 0.1 - 2, O: 0.1 - 1.5, Sulfur: 0.5 - 6(higher S=loss of energy; react with H2O to
produce H2SO4, which is also bad for engine), Metals - less than 1000ppm
Production(in refinery) – Fractional distillation
Heating ~350∘C (crude oil will solidify if temp. is too high), Hydrocarbon fractions separated by b.p.
ISO 8217: Sulfur content - <3.5%(Global), <0.5%(ECA). Flash point for all fuels in engine rm -
>60℃. Al + Si – check for remains of catalyst after cracking. ULO limit: Zinc(<15mg/kg),
Phosphrous(<15mg/kg), Calcium(<30mg/kg).
Fuel properties - Transport properties
Density: p=m/v (r/s with mass and vol.).
Also shows specific energy & ignition quality
- Needed for: Quantity calculation and to choose right purification equipment
- Density at various temp. usually corrected to 15℃ with use of ref. table (density affected by temp.)
Viscosity: Measure of the resistance of a liquid to flow (shear)
- Recommend viscosity at engine: 12 - 18 cSt
- Knowledge of viscosity is necessary to know: how much heating required for a fuel for transfer
purpose
(filter) and temperature range required for satisfactory injection and combustion (atomiser) .
- Reference temp for Distillate fuel: 40℃ and Residual fuel: 50℃.
, - WAS used as an indicator of fuel quality, no longer an indicator of fuel quality in ISO 821 due to
secondary refining process. Need to consider other fuel properties also.
Critical Temperatures [℃]
Cloud point - only for DMX (diesel) fuel: Lowest temp. at which wax precipitates as fuel is
cooled (filter blockage)It’s the temp where wax starts to crystallised out, seen when clear fuel
becomes opaque.
Pour point: Lowest temp at which fuel ‘just’ remains fluid as fuel is cooled (limit of
pumpability). Any lower temp, fuel will gel and prevent flow
Solidifying point: Highest temp. at which fuel remains solid
Flash point - impt for safety: Lowest temp. at which the air/fuel mixture can be ignited by a
flame or spark (i.e. ignitable mixture in air).
Minimum flash point: Safety measure to minimise fire risk. Fuel to be stored at least 10℃ below
this. Engine room fuel min. value is 60℃. For fuel used for emergency (e.g. for lifeboat) must be
>43℃
Ignition point: Lowest temp. at which air/fuel mixture will spontaneously ignite (i.e. in
normal atm.
w/o external source of ignition) and maintain a flame for more than 5 seconds
Impurities/contaminants - can be removed by on-board or pre-treatment
Water content: Reduces combustion rate & net heat output, Removed by
centrifugal/unassisted separation
Mechanical particles (insoluble in fuel) - e.g. dust, rust, grit, fibres, etc :Causes wear, injector
blockage, Removed by centrifugal separation and filtration
Sodium: Corrosion problems, Removed by water-sealed centrifugal separation
Impurities in RFO (from residue of secondary distillation)
More difficult to burn due to: Impurities such as Na, Vanadium and S that are already
present in crude oil and catalyst materials: Al and Si (Cat fines) from FCC.
Causes problems to combustion chambers, exhaust systems, fuel injectors, fuel pumps
Sulfur: low temp. corrosion, Cat fines (Al + Si): Abrasive wear, Ash-asphaltenes: poor
combustion, failures of exhaust valves and turbochargers (not easily burned), Vanadium: high temp
corrosion
Fuel properties – Ignition and combustion properties
Calorific values/specific energy - quantity of heat produced by combustion
(Net)Lower calorific value (LCV/LHV/NCV): Treats H2O forms as vapour (i.e. assumes that
condensation
heat is not included). Relevant value for combustion engines because water condensation causes
corrosion in exhaust systems (esp. combined with sulfur to form H2SO4)
To serve its purpose – trading, offshore exploration/production/support, fishing, towing,
dredging, research, firefighting, icebreakers, etc
Sufficient strength(Depends on design), stable, maintainable, economical to build & operate
Maneuverability, sufficient power to deliver appropriate speed
Self-sustaining (carry enough fuel, food, fresh water & components with high reliability)
Safetyminimize
chance of damage from fire, storm, collision/grounding
Basic Definitions
Classification society: independent org providing guidance & certifications in designing,
building & maintaining(hull, machinery, equipment)
Port(left), Starboard(right), bow/forward(front), stern/aft(back)
Decks(Main:Primary deck, Bridge:deck which navigation equipments are housed, Lifeboat)
Shell: watertight plating around sides & bottom, Superstructure: anything above main deck –
generally referring to accomodation area, Bulkheads: partition within the hull of the ship
Units of measurement
Length: 1 feet = 0.3048m, 1 nautical miles = 1852m/1.15miles/6080ft
Speed: 1 knot = 1 nautical mile/hour = 0.514 m/s
Weight: 1 tonne = 1000kg, Volume: 1 tonne = 1000 cubic feet
Water Density
Density = mass/volume (kg/m3), Specific gravity=density of a substance/density of water (no
unit)
ρ(fw)=1ton/m3=1000kg/m3 (specific gravity of water=1) , ρ(sw)=1.025ton/m3=1025kg/m3
Water(nearly incompressible)ρ doesn’t vary with depth. Density ↑ when salinity ↓ & temp
↑
Tonnage
Volume: Gross tonnage(GT/GRT): total vol. of ship, Net tonnage(NT/NRT): vol. of revenue
earning spaces (i.e. cargo spaces) – GT and NT are measured in tons (1 ton = 1000 cubic feet)
Weight: Deadweight tonnage(DWT): how much mass a ship can safety carry(incl. cargo, fuel,
ballast, stores, crews, etc), Lightweight: weight of ship without any cargo, water, fuel, etc (scrapyard
based on lightweight, only interested in weight of steel) – all measured in tonnes
Displacement: Archimedes Principle: Displacement weight of ship = weight of water displaced by
ship
Ship dimensions
, LOA: Max. length of hull from forward-most point on bow to end of stern(rudder not
included)
LWL: Length of designed waterline (above is freeboard, below is draft)
LBP: Forward p.(FP) is forward end of designed WL, aft p.(AP) is centre of rudder stock
Draft(T): vertical distance from deck to waterline
Air draft: vert. distance from waterline to highest point of ship
Depth(D): vertical distance from deck to keel
Centre of buoyancy (B): CG of the displaced vol. of water.
Centre of gravity (G): line of action of CG and CB must be along the same line when ship is
still
Waterplane area: the section through the hull taken at it’s intersection with water
Lecture 2: Properties of Marine Fuel
Marine Fuels
Crude Oil - Composition by weight(%):
C: 83 - 87, H: 10 - 14, N: 0.1 - 2, O: 0.1 - 1.5, Sulfur: 0.5 - 6(higher S=loss of energy; react with H2O to
produce H2SO4, which is also bad for engine), Metals - less than 1000ppm
Production(in refinery) – Fractional distillation
Heating ~350∘C (crude oil will solidify if temp. is too high), Hydrocarbon fractions separated by b.p.
ISO 8217: Sulfur content - <3.5%(Global), <0.5%(ECA). Flash point for all fuels in engine rm -
>60℃. Al + Si – check for remains of catalyst after cracking. ULO limit: Zinc(<15mg/kg),
Phosphrous(<15mg/kg), Calcium(<30mg/kg).
Fuel properties - Transport properties
Density: p=m/v (r/s with mass and vol.).
Also shows specific energy & ignition quality
- Needed for: Quantity calculation and to choose right purification equipment
- Density at various temp. usually corrected to 15℃ with use of ref. table (density affected by temp.)
Viscosity: Measure of the resistance of a liquid to flow (shear)
- Recommend viscosity at engine: 12 - 18 cSt
- Knowledge of viscosity is necessary to know: how much heating required for a fuel for transfer
purpose
(filter) and temperature range required for satisfactory injection and combustion (atomiser) .
- Reference temp for Distillate fuel: 40℃ and Residual fuel: 50℃.
, - WAS used as an indicator of fuel quality, no longer an indicator of fuel quality in ISO 821 due to
secondary refining process. Need to consider other fuel properties also.
Critical Temperatures [℃]
Cloud point - only for DMX (diesel) fuel: Lowest temp. at which wax precipitates as fuel is
cooled (filter blockage)It’s the temp where wax starts to crystallised out, seen when clear fuel
becomes opaque.
Pour point: Lowest temp at which fuel ‘just’ remains fluid as fuel is cooled (limit of
pumpability). Any lower temp, fuel will gel and prevent flow
Solidifying point: Highest temp. at which fuel remains solid
Flash point - impt for safety: Lowest temp. at which the air/fuel mixture can be ignited by a
flame or spark (i.e. ignitable mixture in air).
Minimum flash point: Safety measure to minimise fire risk. Fuel to be stored at least 10℃ below
this. Engine room fuel min. value is 60℃. For fuel used for emergency (e.g. for lifeboat) must be
>43℃
Ignition point: Lowest temp. at which air/fuel mixture will spontaneously ignite (i.e. in
normal atm.
w/o external source of ignition) and maintain a flame for more than 5 seconds
Impurities/contaminants - can be removed by on-board or pre-treatment
Water content: Reduces combustion rate & net heat output, Removed by
centrifugal/unassisted separation
Mechanical particles (insoluble in fuel) - e.g. dust, rust, grit, fibres, etc :Causes wear, injector
blockage, Removed by centrifugal separation and filtration
Sodium: Corrosion problems, Removed by water-sealed centrifugal separation
Impurities in RFO (from residue of secondary distillation)
More difficult to burn due to: Impurities such as Na, Vanadium and S that are already
present in crude oil and catalyst materials: Al and Si (Cat fines) from FCC.
Causes problems to combustion chambers, exhaust systems, fuel injectors, fuel pumps
Sulfur: low temp. corrosion, Cat fines (Al + Si): Abrasive wear, Ash-asphaltenes: poor
combustion, failures of exhaust valves and turbochargers (not easily burned), Vanadium: high temp
corrosion
Fuel properties – Ignition and combustion properties
Calorific values/specific energy - quantity of heat produced by combustion
(Net)Lower calorific value (LCV/LHV/NCV): Treats H2O forms as vapour (i.e. assumes that
condensation
heat is not included). Relevant value for combustion engines because water condensation causes
corrosion in exhaust systems (esp. combined with sulfur to form H2SO4)
