History and Development Flashcards
1
Q
How much is 1 bbl in litres, US gallons and imperial gallons?
A
- 159l
- 42 US gal
- 35 imperial gal
(bonus) 6-7 bbls per tonne depending on density
2
Q
How is demand for tankers usually measured?
A
Tonne miles - meaning that if the distance travelled increases, so does demand (e.g. during the Suez Canal closures in 1956 and 1967)
3
Q
Define tonne miles
A
- A unit of measurement quantifying the amount of cargo transported over a certain distance
- Used to measure tanker demand, as well as efficiency of shipping operations or to compare the performance of different vessels/transport routes
- Calculated by multiplying the weight of the cargo in tonnes by the distance traveled in miles
4
Q
Define LOA
A
length overall - extreme length of vessel
5
Q
Define LBP
A
length between perpendiculars – length of a ship between forward and after perpendiculars measured along the summer load line
6
Q
Define breadth moulded
A
Ship’s width measured inside the shell plating
7
Q
Define beam
A
extreme width of a vessel
8
Q
Define draught/draft
A
the depth of the lowest point of a vessel below the waterline
9
Q
Define depth of a vessel
A
distance from the upper deck to the lowest point of the keel measured at the ship’s side
10
Q
Define capacity. How does this differ in tankers vs other vessels?
A
the cargo carrying volume, measured in bbls or cubic metres. The capacity of the carriage of oil is usually 98% of the total volume of a tanker’s cargo and slop tanks, to allow for possible expansion of the liquid cargo due to temperature changes
11
Q
Define BCM
A
bow to centre of manifolds – used to assess the position of the loading arm carrying the shore pipeline to the ship on an assigned berth - the distance measured from the bow (front) of a vessel to the center of the cargo manifolds. Cargo manifolds are the piping systems on a ship used for loading and unloading cargo
12
Q
Define air draught
A
distance from the waterline to the highest point on the uppermost structure of a ship (e.g. mast/similar)
13
Q
Define KTM
A
keel to top of mast – distance from the keel to the highest place on the uppermost mast
14
Q
What variations of tonnage are used to measure ships?
A
- ldt - light displacement tonnage (aka lightweight or lightship weight)
- dwt - deadweight tonnage
- displ - displacement
- dwcc - deadweight cargo capacity
15
Q
Define ldt
A
light displacement tonnage (AKA lightweight, lightship weight) – the weight of a vessel including engines, boiler water, lubricating oils and cooling water system – used when negotiating the sale of ship for demolition
16
Q
Define dwt
A
deadweight tonnage – the difference between a ship’s lightweight and loaded displacement, which is equal to the weight that can be loaded onto a vessel, including cargo, fuel, stores, water ballast, fresh water, crew and passengers. When describing tankers, it’s usual to use its summer deadweight (sdwt)
17
Q
Define displ
A
the lightship weight plus the deadweight of a vessel, equal to the total weight of water displaced by the vessel at an applicable draught
18
Q
Define dwcc
A
deadweight cargo capacity – deadweight tonnage minus bunkers, water and constant weights, equal to the cargo capacity of a vessel at a particular time and given draught
19
Q
Describe the typical traits of a VLCC
A
- Carries around 2m bbls
- Loads WAF, USGC, ME
- Around 320,000 dwt
- Most VLCCs can only transit the Suez Canal part laden even though the draught limit is 20.1m due to length and beam restrictions relative to draught
- Typical loaded draught 20-22m
20
Q
Describe the traits of a typical suezmax
A
- Carries around 1mb
- Loads WAF, ME, Med, NAF, North Sea, Baltic and LATAM
- Around 200,000 dwt
- Can transit Suez Canal fully laden
- Typical loaded draught 16m
21
Q
Describe the traits of a typical aframax
A
- Carries around 600kb
- Typically the trampers of global trade, capable of loading from numerous ports (including Brazil, Mexico, N Sea, Baltic, Northern and FE Russia, NAF, Black sea, ME, Med and SE Asia
- Can also discharge at most ports
- Around 120,000 dwt
- Typical loaded draught 12m
22
Q
Describe the traits of a typical Panamax
A
- The name originally referred to dry cargo vessels before being adopted by the tanker industry to describe a vessel that could transit the Panama Canal before its expansion (max beam 32.2m)
- Around 350-400kb capacity
- Trade is focused in the Americas
23
Q
Describe the traits of a typical MR tanker
A
- ‘Medium range’ – usually carries products
- Able to cover many global trade routes
- Capacity of 30-55kt
24
Q
Describe the traits of a typical LR1
A
- ‘Long range 1’ – renamed from ‘large range,’ which is still sometimes used
- Roughly equal to Panamax, but usually specialises in clean products and therefore have coated cargo tanks
- 55-80kt capacity, however clean LR1s can only hold around 70kt before cubing out due to density
- Most usually only carries 55kt of CPP, usually from the ME to Europe or the FE
25
Describe the traits of a typical LR2. What's an LR3?
* Roughly equal to afras or suezes in size (80-160k dwt)
* Used for the London Tanker Broker’s panel for its AFRA (average freight rate assessment) evaluations
* Typical trade would be 75kt of CPP from the ME to FE
* Suezmaxes larger than this with coated tanks are sometimes called LR3s and can carry 120-130k dwt before cubing out
26
What crude oil tanker traits are typically shared between all sizes of vessel?
* Can usually carry three different grades separately
* Simple pumping and pipeline systems for load/discharge
* Straightforward to build/operate due to the homogenous nature of the cargo (small amounts of contamination are unimportant)
* Most crude tankers below 150k dwt are capable of heating the cargo to maintain pumpability
* Since 1992, all newbuild tankers must comply with the International Convention for the Prevention of Pollution from Ships (Marpol), meaning they must be fitted with a crude oil washing system (COW) and an inert gas system (IGS).
* Single hull tankers were phased out of all deepsea trades by 2015; most have since been taken out of service, but some trade in internal cabotage trades or between non-Marpol ratified countries
27
Describe how tankers ballast
* Unladen tankers require about 1/3rd of their dwt on board as ballast to ensure it can sail safely - for this, sea water is used
* Segragated ballast is loaded into double-bottom and side ballast tanks within the double hull
* This ballast must be released in order to load cargo - regulations are in place to prevent the introduction of invasive species via ballast water under the 2004 water ballast management convention (which came into force in 2017)
28
Describe COWs
* Crude Oil Washing
* After discharge, some clingage remains stuck to tank walls, alongside sand or waxy deposits. These residuals lead to some cargo loss
* To prevent this, cleaning guns are fitted to the tanks; during discharge, around 10% of the cargo is recirculated under pressure through these rotating guns to wash down the clingage, meaning that much less residue is left. Any residue that does remain can be removed via water washing/gas freeing
* Water washing may also be required if the tanks need to be physically entered by a person for maintenance/dry docking, or if the previous crude had specific characteristics which may be problematic for the next load (e.g. high waxes or mercaptans)
29
Describe IGSs
* Inert Gas Systems
* Crude oil is volatile and gaseous, and COW systems release large quantities of flammable vapours. To prevent this, tanks with COW systems must be inert – with oxygen levels below 5% from the plant and 8% in the tanks
* This prevents explosions (explosions require fuel, oxygen and ignition – e.g. a spark from static electricity)
* Normal air contains around 21% oxygen. Hydrocarbons cannot burn in air below 11% oxygen (hence the 8% limit by volume in the atmosphere of the ship’s tanks implemented by the IMO)
* IGSs work by increasing inert gasses in tanks, such as CO2 or nitrogen. These gasses are supplied by exhaust fumes from the ship’s engines (If the engines don’t produce enough, an auxiliary boiler or inert gas generator can be fitted). These inert gasses are scrubbed and cooled before being injected into the tanks
* As cargo levels fall, more inert gas is pumped in to prevent cargo gasses being replaced by air (which is above the safety threshold for preventing explosions)
30
What product tanker traits are typically shared between all sizes of vessel?
* Most cargoes carried by product tankers are intended for use without further refining, so cleanliness and the avoidance of contamination is key – because of this, product tankers’ tanks are usually coated with epoxy resin or similar inert plastic coatings to prevent the cargo coming into contact with bare steel (steel can be eroded by some products, leading to contamination, and coated tanks are easier to clean)
* Tank cleaning in product tankers is done via high pressure fresh water
* Typically product tankers can segregate up to 4 types of cargo (particularly CPP), separated via double valves to prevent the mixing of grades/altering of properties
* Changing a tanker between CPP and DPP requires meticulous cleaning, which is expensive; this means that products tankers typically do not swing between CPP and DPP
* DPP tankers require heating coils or heat exchangers to enable the pumping of viscous and high density grades of fuel
31
Why are cargo pumps fitted at the bottom of ships?
Cargo pumps are fitted at the bottom of ships because the height that a pump can push cargo is limited only by the power of the pump.
32
Where are cargo pumps housed on tankers, and why?
Cargo pumps are housed in separate pump rooms, usually in front of the engine room and behind the tanks, to allow for easy maintenance and reduce the risk from any gases that may escape pump seals.
33
What is the difference between how tankers discharge and load cargo?
Tankers use their own pumps to discharge cargoes, while shore-based pumps are used to load cargo.
34
What type of pumps are commonly used on the largest tankers, and what powers them?
* Centrifugal pumps are commonly used on the largest tankers. These pumps are capable of high discharge rates and can be driven by steam, diesel, or electricity.
* Power sources for centrifugal pumps are not housed in the pump room due to safety concerns. They are driven by a shaft from the engine room bulkhead, which is sealed in a gas-tight gland to prevent pump room gases from entering the engine room.
35
What are stripping pumps, and why are they used alongside centrifugal pumps?
Stripping pumps are usually small reciprocating pumps used to handle the final metre of cargo in tanks, as centrifugal pumps typically leave this residue.
36
How do reciprocating pumps differ from centrifugal pumps?
Reciprocating pumps are less powerful than centrifugal pumps but can handle a wider range of cargoes. They also have slower discharge rates and are typically used on smaller ships.
37
Besides reciprocating pumps, what types of pumps are used for tank stripping and washing, and how do they work?
Eductors are used for tank stripping and washing. They are driven by cargo or slop fluid and are located in the pump room. For tank washing, the driving fluid comes from the secondary slop tank, which is recirculated into the primary slop tank.
38
What factors need to be considered when choosing a pipeline system for a ship?
**Protection of cargo**
* Cargo load and discharge carries the risk of contamination from other grades being carried or seawater
* This is less important for crude carriers, as some contamination is acceptable as the crude will be refined before being sold to consumers, however in finished products contamination is unacceptable
* Because of this, products tankers have more complicated and sophisticated pipe systems than crude carriers
**Speed of discharge**
* Tankers aim to spend as little time as possible in port to maximise earnings and to free up jetty capacity at terminals. Most CPs require the entire cargo to be discharged within 24hrs
* Restrictions on speed of cargo discharge are viscosity, diameter of pipe, bends in the pipe and height of receiving tanks, which all impact back pressure. Because of this, large, straight pipes are preferred where possible
Pipes are costly to install and maintain, so shipowners will choose the most simple system possible that’s adequate for their intended trade
Pipes made from mild steel are cheap but vulnerable to corrosion, particularly in the ballast system where they are in contact with sea water
Alternatively pipes can be made from glass reinforced plastic (GRP); these are most commonly found on chems carriers. Some chems carriers use stainless steel, particularly for proponic and nitric acids, as these require the most specialised handling
39
Describe ring main pipe systems
Ring main – pipes running around the bottom of a ship like a ladder. The main advantage is that there are always at least two lines running the full length of a ship, meaning there are alternative routes for loading and discharge. Ships can be fitted with two ring mains, meaning there are four full-length pipes available, making this the most flexible option. The ring main is more expensive than other systems. Crossover systems can be added to connect the port and starboard mains pipeline systems, but care must be taken to avoid contamination.
40
Describe a block pipeline system and compare it to the ring main system
Block system – A single pipeline runs the full length of the ship, with another that runs about two thirds of the way and another covering around a third of the ship’s length from the back. This system is less flexible than the ring main system as only one line reaches the forward section, however it is simpler than the ring main and is ideal for ships fitted with three cargo pumps. This is the most widely used system, and whilst there is a slight disadvantage with regards to the lack of flexibility for forward tanks, this is mitigated by greater flexibility for the rest of the cargo area.
41
What are stripping lines?
These connect to the stripping pumps for discharging the final volume of cargo from larger tanks and are much smaller than main cargo lines due to smaller quantities and slower pumping rates. These must also be considered when segregation of cargo is important. Stripping lines are becoming less common as more efficient methods of cargo removal are adopted (e.g. vac-strips and priming systems)
42
What are direct loading lines?
Loading lines leading directly into certain tanks or a pipeline system without passing through the pump room. Useful for segregating grades. On some tankers it is possible to fully load without any liquid passing through the pump, meaning segregation is almost guaranteed
43
What is a stern discharge line?
A line with a loading connection at the stern of a tanker, used in ports where vessels berth with the stern to the jetty. These kinds of jetties, where only one line can be connected to the ship, load and discharge rates are very slow
44
Describe pump room lines
The most complicated pipeline system on a tanker, where pipelines allow for any pump to be connected to any pipe. Each cargo pump must be in line with one of the ship’s fore or aft pipelines, but behind the ‘bottom crossover’ (a line connecting one side of the ship to the other). This makes it possible to connect any cargo pump to any of the main pipelines or sea suctions. There will also be a top crossover, allowing each pump to connect to each discharge line. Discharge lines are connected by pump room droplines. There is a bypass for each cargo pump so it can be isolated whilst loading.
45
What are gas lines? How are they used in conjunction with CLSs and VRLs?
Gas lines – Used to allow the air and gas displaced during loading to escape, and to allow air or inert gas (in conjunction with an IGS) into tanks while discharging. Whilst in transit, weather changes can cause expansion of liquid cargoes and the gas must be allowed to escape to prevent a dangerous build up of pressure (and visa versa). During loading, gas is naturally forced out of a tank; a closed loading system (CLS) prevents this gas from being released and is returned to shore via a vapour return line (VRL).
46
What are valves, how are they operated, and what maintenance is required?
Valves control the flow of oil through a pipeline. They can be hand operated via a spindle on the deck or power operated via remote hydraulic controls. Remote values are usually controlled via a tank control room adject to remote tank level indicators.
Valve maintenance must be carried out by dismantling the valve and replacing any worn-out parts, and cleaning any debris/rust that may have accumulated in the seat of the valve.
47
What are gate valves
The most common type of valve on a tanker. These close pipes via a flange or spade controlled via a nut which is connected to a screw, controlled via a spindle (it’s screwed open or closed).
48
What are tank valves
Control the flow of oil into and out of a tank. Always situated at the back of a tank, often alongside another at one of the bottom corners to aid draining. Suction pipes are fitted to these valves, which usually extend to around 2-9cm from the tank bottom
49
What are crossover valves?
control the flow of oil in a from one side of a vessel to the other within a pipeline system, enabling the two fore and aft pipes to handle different grades without contamination through athwartship (side to side) sections of the lines
50
What are master valves?
control the flow of oil between the fore and aft sections in a pipeline, used to isolate sections of cargo lines to segregate different grades
51
What are gate valves?
located in the ship’s loading manifold where it connects to shorelines. Drip trays are fitted underneath to catch spills when lines are connected or disconnected. These valves must always remain open during the load process to prevent the flexible shorelines from bursting under pressure (this is also true of the tank valves when switching between loading tanks).
52
What are bulkhead valves?
situated in the bulkhead between two tanks, used to allow liquid to flow from one tank to another. In a tanker with a freeflow system, this is the only way to transfer cargo between tanks.
53
What are sea valves?
– located at the bottom of the pump room at each side of the ship, where they may be connected by a pipeline. They are used in ballast operations to allow seawater onto or off of a ship.
54
What are parcel tankers?
* Trade in veg oils or volatile chemicals
* Absolutely no contamination is acceptable, as the chemicals can become dangerous or have their properties irreparably altered, and veg oils are intended for consumption and so must be handled with the highest care
* The equipment required for this segregation and specialised handling is very expensive for a vessel of its size
* Depending on what it’s intended to carry, its tanks can be coated with zinc silicate, epoxy resin or polyurethane (or in extreme cases such as highly corrosive acids, stainless steel)
* These coatings prevent chemical cargoes from reacting with the tanks, damaging both the ship and the cargo, as well as making it easier to clean the tanks to very exacting standards
* The most sophisticated parcel tankers have separate deepwell pumps and pipeline systems for each tank, allowing them to carry multiple chemicals at once without risk of cross contamination
* Shippers will need to know the previous three cargoes carried to minimise the risk of damage to their cargo. This makes the ability to carry multiple cargoes separately more important, as shippers within this constraint will need to reduce ballast time to a minimum but carrying cargoes for multiple shippers simultaneously
* Most common routes are PG to WC India, Ulsan or Med/ARA; ARA to the USGC; and sometimes USGC back to ARA.
* These types of tankers can be switched to CPP depending on market conditions
55
What are the main types of gas carriers, and what gases do they transport?
Gas carriers are split into LNG carriers (transporting ethane and methane) and LPG carriers (transporting propane and butane). LPG carriers can also carry ammonia and some chemical gases.
56
How is LNG transported, and what makes LNG carriers unique?
LNG is transported at -162°C to keep it liquefied. LNG carriers have insulated but non-pressurized tanks and use spray cooling to adjust temperature. They carry LNG above its boil-off temperature, using the boil-off gas as fuel, though newer vessels have reliquefaction systems to convert some of it back into LNG.
57
How do LPG carriers differ from LNG carriers in cargo handling?
LPG (propane and butane) must be kept at high pressure (10-12 bar) or cooled to -50°C to remain liquid. Unlike LNG carriers, LPG carriers are usually traded on the spot market rather than long-term contracts.
58
Why are gas carriers considered highly specialized vessels?
Gas carriers are the most expensive cargo ships to build and operate. They require highly trained personnel both at sea and onshore. Traditionally, LNG carriers operated on 20-year contracts with dedicated export facilities, but spot and short-term contracts are becoming more common.
