There are two (2) types of bulk cargoes Dry Bulk Cargoes and Wet (Liquid) Bulk Cargoes.
- Dry Bulk Cargoes
- Dry Non-Bulk Cargoes
Dry Bulk Cargoes
The primary condition for loading any cargo is that the ship’s holds have to be dry and clean. The level of cleanliness depends on the cargo to be loaded. A ship about to load bulk grain (Grain Clean Certificate) have to be extremely cleaner than a ship about to load coal or iron ore. Nevertheless, the level of cleanliness even for these cargoes differs broadly depending upon the type of cargo. For instance, high-quality coal with low-sulphur content can not tolerate residues from high-sulphur ores. The ship has to pass a cargo hold cleanliness survey before the loading can start so all the residues of the previous cargo have to be removed before the ship arrives at the loading port. Usually, stevedores do not sweep clean the holds that leave a certain amount of cleaning work to be fulfilled by the ship’s crew members. Furthermore, the ship must always stay in safe trim not only for the sea voyage but also during the loading operation to avoid undue stress to the hull of the ship.
Customarily, an Independent Cargo Surveyor is appointed for Sensitive Dry Bulk Cargoes. In developed ports, cargoes are loaded by chute or grabs, so no additional cargo trimming is required for the ship to be in seaworthy trim. Many Charter Parties stipulate that the cargo will be loaded and spout-trimmed free of expense to the ship.
In undeveloped ports, hand-operated trimming may be required to spread the cargo across the holds. Cargo trimming prevents the risk of the cargo shifting dangerously during the voyage. Shifting might happen if the cargo is simply left to take up its natural Angle of Repose leading to a peaked pyramid shape.
Dry Bulk Cargo Risks
Bulk Grain: before loading can start the ship’s holds must be Grain Clean. Moreover, bulk grain is free-flowing cargo so there is a risk of the cargo shifting when the ship rolls in bad weather. Rolling might cause a list from which recovery is impracticable and capsize becomes unavoidable. The Ship Master has to present to the Surveyor ship’s stability calculations for checking and approval based upon the data in the ship’s Grain Book which must be approved by the Flag State. Grain Book affirms how many holds can be partly loaded (slack loading). Great care has to be taken in calculating precisely how much bulk grain the ship can load and safely navigate. Not all dry bulk cargoes flow and ships loading non-shifting cargoes such as Iron Ore can be partly loaded (slack loading).
Scrap: metal scrap may include heavy or sharp pieces that can damage the ship’s frames. Oily steel turnings may cause spontaneous combustion and steel can burn in such conditions. Even well-drained motor blocks, engines, and machinery may still drip some oil during the sea voyage which is extremely hard to remove from the ship’s holds.
Coal: methane-rich is subject to spontaneous heating and combustion. The Shipowners and Ship Managers must ensure they identify which coal types are combustion-prone. Virtually all coal cargoes propagate inflammable gas and so ventilation of the holds is crucial although natural ventilation is enough.
Fishmeal: is subject to spontaneous combustion. Customarily, the total quantity of bulk fishmeal cargo is set by shore weighing. The Ship Master should double-check the amount through a draft survey.
Sulphur: can damage the ship hold’s steel plates unless it is coated with a lime-wash before loading starts.
Dry Non-Bulk Cargoes
The loading of dry non-bulk cargoes is a more complicated, labor-intensive, and slower process than dry bulk cargoes. The dry non-bulk cargoes have a much wider range and obstacles. Dry non-bulk cargoes cannot be simply poured into the ship’s holds like dry bulk cargo. Dry non-bulk cargoes have to be delicately stowed and, if required, lashed and secured. Traditionally, dry non-bulk cargoes are calculated by shore tally however the correctness of such tallies is often poor and in some ports, the tally is almost non-existent. The Ship Master should arrange a crew member to spot-check the tally.
Dry Cargo Risks
Bagged Cargoes: the ships’ holds have to be clean and unobstructed. All bagged cargo is prone to wear and tear during loading and discharging operations. Cargo battens have to be installed on frames to reduce the risk of condensation damage.
Bagged Fishmeal: bagged fishmeal is subject to spontaneous combustion.
Bagged Rice: the ship’s holds have to be completely cargo batten fitted with ventilation channels.
Bagged Ammonium Nitrate: is subject to spontaneous combustion, particularly if the Nitrogen content of the Ammonium Nitrate is above 27%.
Steel: the weight of every piece of steel especially steel coils have to be checked to ensure that the maximum stowing permitted on the ship’s tank tops is not exceeded. Unprotected steel soon becomes rusty and that rust raises cargo claims.
Logs: stanchions have to be erected on deck to load logs on deck. Additionally, the ship has to provide chains to keep the logs on deck from shifting. Floating Logs (Floaters) are loaded directly from the water, crew members should be careful because wet and drying out the hold can be challenging. Logs may cause damage to the ship if not loaded or discharged carefully.
Unit Loads: have to be cautiously loaded and lashed to restrict movement during the voyage.
Creosoted Timber: such as telegraph poles, railway sleepers may leave a persistent odor in the holds which may taint future cargoes.
Stowage Factor (SF)
The Stowage Factor (SF) is the density of the cargo in the ship’s hold. A ship has only a limited volume (cubic capacity) in the holds. Therefore, when light cargo is loaded, the ship’s holds are full before all the ship’s DWCC (Deadweight Cargo Capacity) is utilized. On the other hand, when heavy cargo is loaded, the full DWCC (Deadweight Cargo Capacity) can be reached with space still available in the holds but unusable. Imperial System is still used in Stowage Factor (SF) calculations.
While metric ratios of 1 cubic metre to 1 tonne are now commonly used, the Imperial equivalents of 40 cubic feet to one ton are still frequently seen. Both units are given in the examples below conveniently rounded where appropriate.
Stowage Factor (SF) Example:
A ship of 56,000 DWCC with a grain cubic capacity of 71,000 m3 (cubic meters) or 2,500,000 ft3 (cubic feet) can load:
- 56,000 metric tonnes of bulk phosphate has a Stowage Factor (SF) of around 0.90 m3/t (32 ft3/ton). The ship has in fact space for 71,000/0.90 = 78,888 metric tonnes (2,500,000/32 = 78,125 tons) bulk phosphates but the ship can only take 56,000 metric tonnes in weight before her load-line is submerged
- 48,299 metric tonnes of bulk grain has a Stowage Factor (SF) of around 1.47 m3/t (52 ft3/ton). 71,000/1.47 = 48,299 metric tonnes (2,500,000/52 = 48,076 tons). The ship has spare DWCC and could load more cargo but there is no more space in the ship’s holds.
The Stowage Factor (SF) of the cargo is of vital importance to shipbrokers who are planning the employment of the ship. To obtain the same income a higher freight rate per tonne will have to be negotiated for a lighter cargo. The Ship Master has to be notified so that he can manage the loading course to keep the ship in a safe trim. The Ship Master has to be informed if the cargo consists of two or more different commodities, each with a different Stowage Factor (SF) so that the Ship Master can prepare the stowage in such a way as to maintain the ship in trim.
Dangerous Cargoes and Polluting Cargoes
The International Maritime Organisation (IMO) regulates the areas of pollution, safety, and environmental protection. The international carriage of Dangerous Cargoes and Polluting Cargoes are governed by the IMO International Maritime Dangerous Goods Code (IMDG Code). IMO International Maritime Dangerous Goods Code (IMDG Code) supplements any local laws that apply, to the extent that they outline the minimum standards that must be adopted. In some maritime nations, there are local state laws that have more stringent requirements for dangerous goods. The shipowner must be completely aware of any modifications applying to dangerous cargoes during loading or discharging operations and on the sea voyage. Many countries apply similar regulations onshore to the shipper who is obligated to label anything containing dangerous goods. Additionally, dangerous good shippers have to complete documentation that stipulates the nature and hazards of the goods when they are on the move by any form of transportation. IMO International Maritime Dangerous Goods Code (IMDG Code) aka The Blue Book was published in five volumes and it is updated when a hazard occurs which has not happened before, or a new dangerous cargo comes into the shipping market. Usually, state modifications to the Maritime Rules are enacted by governments and distributed as Notices to Mariners.
Dangerous Goods Declaration
Identified dangerous cargoes are assigned a Class and a UN number which detail the nature of the hazard and the type and amount of packing that is required for that particular dangerous cargo. The dangerous good shipper is required to sign a declaration included in the Dangerous Goods Shipping Note (DGN) which is a declaration confirming that the goods have been packed by the IMDG Code. Dangerous Goods Shipping Note (DGN – Declaration) must incorporate:
- Technical Name
- Trade Name
- UN number
The package, the container, or the carrier in which the dangerous goods are carried must also have the appropriate diamond-shaped warning label attached to them.
IMO International Maritime Dangerous Goods Code (IMDG Code) requires segregating the dangerous cargoes onboard ships. Some cargoes when mixed can generate catastrophic results.
Dangerous Cargoes Classification:
- Class 1 Explosives (Military and Commercial)
- Class 2 Gases
- Class 3 Flammable Liquids
- Class 4 Flammable Solids
- Class 5 Oxidising Agents
- Class 6 Poisonous (Toxic) Substances
- Class 7 Radioactive Substances
- Class 8 Corrosives
- Class 9 Miscellaneous Dangerous Substances
Dangerous Cargoes Classification aims:
- Dangerous goods are packaged carefully and suitably labeled by the producer
- Dangerous goods are precisely stowed during land transportation and onboard ship
- Employees associated with the shipment of dangerous goods understand how to deal with spillage, and what steps to take if a fire breaks out in the same section
- Employees know whom to contact for information
The significant point of the separation of different dangerous cargo classes onboard ships is that it may be required for two distinct classes to have between them either one steel bulkhead or in some cases, two steel bulkheads. Regularly, container ships and general cargo ships have enough decks and bulkheads as well as the separation of steel containers themselves to be able to carry most of the dangerous cargo offered on any one voyage although even this may be a problem for cargo that must be carried on deck. The carriage of dangerous cargo on the Ro-Ro ferry is risky. A Ro-Ro ferry may not have enough decks or bulkheads to achieve decent segregation of trucks that may be carrying opposite classes. Therefore, Ro-Ro ferry operators should be extremely careful when dangerous cargoes are booked. Normally, ships carrying Class 5 Dangerous Cargoes do not carry any other classes, and the Ro-Ro ferry operators attempt to plan that no more than one class is taken on one ship.
IMO International Maritime Dangerous Goods Code (IMDG Code) has special rules for the carriage and separation conditions of Class 1 (Explosives) cargoes. Furthermore, many ports do not allow any Class 1 (Explosives) cargoes within port limits. Some countries do permit the IMDG Code exceptions of such as fireworks, safety ammunition, etc in limited quantity and based on direct removal from the port area. Most ports also have very stringent restrictions on Class 1 (Explosives) cargoes remaining on board in transit. Most maritime nations have one or more special berths where explosives may be loaded or discharged.
Dangerous Cargoes Manifest
Ships transporting dangerous goods must have onboard Dangerous Cargoes Manifest and a copy of the Dangerous Cargoes Declaration for each item of cargo. In many countries, there are quite stringent rules relating to the ability of the carrier through its local ship’s agent to present details of dangerous cargoes carried to the authorities. Before accepting dangerous cargo, the Ship Manager must examine:
- Hull Underwriters or P&I Club (Protection and Indemnity Club) have to be notified. P&I Club (Protection and Indemnity Club) should have valuable supplementary information and guidance for the loading, stowing, and discharging of dangerous cargoes
- Adequate onboard stowage conditions
- Extra payment to the crew members
Bill of Lading (B/L)
Bill of Lading (B/L) has three (3) functions:
- The Ship Master’s Formal Receipt for the cargoes
- Document of Title to the cargoes
- Evidence of the contract of carriage
When cargo is loaded on a ship, Mate’s Receipt is issued. Mate’s Receipt records the nature of the cargo, cargo weight, marks, and condition. From Mate’s Receipt, the Bill of Lading is prepared. Oftentimes, shipowners or ship managers will come upon demands that the Bill of Lading be endorsed:
- Freight Prepaid Bill of Lading (B/L) or Freight Paid Bill of Lading (B/L): In this situation, Bill of Lading (B/L) also becomes a receipt for the freight. Some consigners require that the Bill of Lading (B/L) be so endorsed against a promise to pay the freight later. It must be realized that once the Bill of Lading (B/L) is marked Freight Prepaid Bill of Lading (B/L) the consignee is entitled to demand delivery of the goods at the destination. If the shipper’s promise to pay the freight has not been fulfilled, the shipowner lost the security of the lien on the cargo for the freight.
- Clean Bill of Lading (B/L): This is a declaration that the cargo is in sound condition. Regrettably, some shippers request a Clean Bill of Lading (B/L) even though the cargo is not in sound condition. This practice is fraudulent and defending a cargo claim practically non-existent. Particularly, when cargo is sold under a Letter of Credit (L/C), the documentary credit requests for Clean Bill of Lading (B/L) and the banks will not negotiate the credit if it is claused about cargo condition.
All Bills of Lading are marked weight, quality, and quantity unknown. The Ship Master should only sign a Bill of Lading (B/L) for a quantity of cargo he believes to be onboard practicing a Draft Survey for comparing the Shore Weight.
Bill of Lading (B/L) is a Negotiable Document (Document of Title). Therefore, the third party who holds the Bill of Lading (B/L) owns the cargo specified on the ship. The Ship Master must only deliver the cargo to the holder of the Bill of Lading (B/L). The Ship Master releases the cargo to the wrong person, the Ship Master becomes liable for the full value of the cargo.
In the case of the non-availability of the Bill of Lading (B/L) at the discharging port, the charterers sign a Letter of Indemnity (LOI) which must be counter-signed by a First Class Bank. Cargo Manifest and Stowage Plan are issued in addition to the Bill of Lading (B/L) after the completion of cargo loading operations.
The Ship Master is obliged to deliver the cargo at the discharging port in the same good order as received at the loading port. Therefore, it is vital for any deficiencies discovered during the loading to be recorded on the Bill of Lading (B/L), failing which the Ship Master is liable for these deficiencies even though these deficiencies were present before shipment. Against a Genuine Cargo Claim, there is no defense. The Ship Manager must take the measures to minimize the risk of being subjected to an Optimistic Cargo Claim. Some countries require a cash deposit against cargo claims before the ship is authorized to sail. To protect the Shipowner’s interest the Ship Manager should secure that:
- P&I Club’s (Protection and Indemnity Club’s) requirement of loading port Pre-shipment Survey and discharging port Independent Survey strictly fulfilled for steel cargoes
- In the event of bad weather during the sea voyage, the Ship Master should present a Note Protest on arrival, in the presence of a Notary Public
- The Ship Manager should arrange for the customs to seal the hatch covers at the loading port
- The Ship Manager should also arrange a Draft Survey at the loading port and discharging port in conjunction with the P&I Club (Protection and Indemnity Club) representatives
- In any issue, the Ship Manager should consult with the P&I Club (Protection and Indemnity Club) and follow their instructions
Wet (Liquid) Bulk Cargoes
The common expressions Oil and Petroleum Products comprise an extremely broad type of Wet (Liquid) Bulk Cargoes. Wet (Liquid) Bulk Cargoes incorporate Black Oils, Gasses, Spiked Crudes, Topped Crudes, Feedstocks, Chemicals, Gasoline, Kerosene, Gas Oil or Diesel.
There are many types of Crude Oils. Crude Oils are broadly divided into two (2) main classes:
- Paraffin-Based Crudes Oils: contain different amounts of paraffin wax and little asphaltic material
- Naphthenic Crudes Oils: contain little or no wax but have a high proportion of asphaltic material
Depending on the temperature, all crude oils are volatile. Consequently, crude oils have an inherent source of inflammable vapors. The Flash-Point of crude oil is the lowest temperature at which sufficient vapor is emitted to reach an inflammable mixture with air. Below the Flash-Point, the vapor blend is too weak and does not ignite. If the vapor blend is over-riched, there will be insufficient oxygen to start the ignition. Between the two levels if there is a source of ignition an explosion will follow. Therefore, all regulations and precautions must be stringently followed during loading and discharging operations.
Crude Oils incorporate sulphur composites in differing amounts. Generally, the Middle East crude oils have a high sulphur content, on the other hand, the Far East, North African, and North Sea crude oils have less sulphur content. The proper handling of each crude type depends upon its characteristics. For instance, the Middle East crude oils require no extraordinary preparation of tanks before loading, and no heating is needed. Tank Cleaning between crude oil cargoes is solely required for ballast purposes and to limit the composing of residues in the tanks. An increase of residues would affect discharging, by blocking the flow of oil across the tank bottoms, so regular tank cleaning is required. Most crude oils are loaded without any additional tank preparation, after well-draining the tanks. However, there are exceptions and before loading Wax-Free Naphthenic Crudes Oils (Tia Juana Pedado, Cabimas, Lagunillas), the tanks should be hot washed and all wax deposits lifted unless the previous cargo had been a wax-free crude or a naphthenic distillate. Wax-Free Naphthenic Crudes Oils are not carried in very large parcels. Wax-Free Naphthenic Crudes Oils require a reasonably high degree of heating. Usually, charterers are unable to arrange for full homogenous Wax-Free Naphthenic Crudes Oils for the larger VLCCs (Very Large Crude Carriers) and ULCCs (Ultra Large Crude Carriers). VLCCs (Very Large Crude Carriers) and ULCCs (Ultra Large Crude Carriers) are homogenous cargo carriers that may nevertheless be required to carry more than one type or quality of crude oil. Crude Oil Segregation requirements are likely to be such that single valve separation and pipeline admixture is quite adequate. Crude Oil Load On Top is practiced with most crude cargoes but not all crude oils are compatible with each other.
Modern VLCCs (Very Large Crude Carriers) and ULCCs (Ultra Large Crude Carriers) are not outfitted to heat the crude oil cargo. Usually, Crude Oils that require heating are carried in ships under 100,000 DWT. When cargo heating is required it must be performed precisely, with neither Overheating nor Underheating taking place. Overheating or Underheating could result in oil cargo loss or damage. Overheating can damage the oil cargo and boil off important light components, while underheating can increase the precipitation of some of the heavier components, increase the viscosity of the cargo causing discharge problems, and thus presumably generate outturn losses. If a waxy crude oil cools too far, the wax starts to precipitate and drops to the tank bottom. The wax will harden on the cold tank bottoms. Therefore, when discharging waxy oil or any high heat cargo, it is critical to immediately strip the tank bottoms while the oil cargo is still liquid and pumpable.
If the temperature of oil cargo is allowed to fall below its Pour Point, oil cargo starts to solidify. No Heat Crudes Oils can solidify if the voyage becomes protracted such as a sudden port strike. Usually, the minimum temperature at which crude oil cargo is to be maintained is 10° Celsius degrees above its Pour Point. It is imperative to adhere as exactly as possible to the charterer’s instructions on when cargo heating should commence and the temperature at which the cargo should be maintained and delivered.
Center Tanks have larger volumes and smaller exposed surfaces. Therefore, it is reasonable to keep a higher temperature in the Center Tanks than the Wing Tanks which lose most heat because of their position. If more than one crude oil grade is loaded and the volumes and segregation systems allow, the higher heat cargo should therefore be stowed in the Center Tanks. If a heating problem issues in one or more tanks, it may be possible to obtain enough overall temperature by circulating the crude oil cargo, but the charterer should be advised in advance in such situations. When discharging oil cargo in low ambient temperatures, it may be required to keep the oil cargo circulating through the deck lines to prevent solidification and a blockage of the lines. In modern tankers, the suction lines pass through the tanks, and the oil cargo in the tanks keeps these lines heated. Where the suction lines are not located in the tanks, it is vital to remove the suction lines after loading to ensure that the oil cargo residing in the suction lines does not solidify on passage. Especially, this is critical with some waxy oil cargoes. Obstacles with wax differ considerably depending on sea and air temperatures. The shipowner’s contractual obligation is to maintain the temperature of the cargo or it may be to increase the temperature if the charterer so requires. If the obligation is to maintain the temperature and the cargo is loaded at a lower temperature, the Ship Master should write a Protest Letter. Increasing the oil cargo temperature may be hard to reach on a short voyage or in unfavorable weather conditions. Furthermore, increasing the oil cargo temperature can be expensive in terms of bunkers.
Inert Gas System
In many maritime nations, tankers over 20,000 DWT are not authorized to load or discharge unless their Inert Gas System is in operation. The quality of the inert gas and the oxygen level in the tanks must be constantly monitored. The inert gas in the tanks must be kept topped up during the sea voyage. The highest level of inert gas is demanded during discharging operation when air could be absorbed into the tanks, and after cleaning (gas freeing).
Cargo Surveyors may need the inert gas pressure in the tanks to be reduced to ullage, dip, or inspect the tanks. Inert gas pressure in the tanks should be reduced per shipowners’ approved schemes. Inert gas reduces visibility in the tanks. Therefore, visual inspection of the inerted tanks is challenging. Additional time is required for de-inerting and cleaning the tanks at the arrival port.
Even though the inert gas is transferred through a scrubber to eliminate solid particles, greyish sediments in the tanks may cause discoloration of clean oil cargoes and risk of contamination. In case of a collision, the inert gas is quickly lost and the air in the tank becomes explosive.
Segregated Ballast Tanks
In the past tankers took ballast water into unwashed cargo tanks and on the ballast passage discharged this oily water into the sea and replaced it with clean seawater. Load-on-Top Methods whereby the tank washings were stored onboard after decanting and discharging overboard as much water as possible, considerably decreased the oil discharging into the sea however this method was not sufficient. The discharge of tank washings or dirty ballast into the sea is now outlawed under the International Convention for the Prevention of Pollution from Ships (MARPOL). All tankers in international trade must comply with the International Convention for the Prevention of Pollution from Ships (MARPOL).
All new building crude carriers over 20,000 DWT that are delivered after June 1982 must have Segregated Ballast Tanks (SBT). United States Coastguard Regulations oblige tankers over 20,000 DWT to have Segregated Ballast Tanks (SBT) or Dedicated Clean Ballast (CBT). Dedicated Clean Ballast (CBT) has its lines, pumps, tanks and it is fully separated from the cargo system.
Tank Cleaning and Crude Oil Washing (COW)
Until the invention of Crude Oil Washing (COW), tanks had to be washed with water. The system used employs high-pressure seawater delivered to the tanks via rotating nozzles like enormous lawn sprinklers. The high-pressure jets reach every part of the tank. Generally, the water used is at ambient temperature. Crude Oil Washing (COW) is washing a tank with crude oil cargo does not seem an obvious way of cleaning the tank. Pumping crude oil through the tank washing machines as each tank is discharged, shifts much of the clingage from the tank sides and the residues and oily sediments from the horizontals and tank bottoms. Crude Oil Washing (COW) consumes a much shorter time and is much more effective than simply natural drainage. Additionally, Crude Oil Washing (COW) removes the solids and semi-solids which would otherwise remain where they have settled out on the horizontals and tank bottoms. After each tank is washed with Crude Oil Washing (COW), the tank bottoms are stripped to a collecting tank from where the collected oil is pumped ashore.
Gas is generated during Crude Oil Washing (COW). This gas is vented from the tank so there is an increase in the loss of important light fractions. Nevertheless, Crude Oil Washing (COW) moves the clingage and deposits to the tank bottoms and increases the total cargo outturn.
Crude Oil Washing (COW) makes the tanks much cleaner so reducing the difficulties of cleaning for ballast purposes and reduces the consumption of burners for subsequent tank washing. This is the main benefit to the shipowner except in those cases when the shipowner might otherwise face a claim for short delivery but the extra crude oil collected and put ashore as a result of Crude Oil Washing (COW). The proportion of the tanks that must be Crude Oil Washed to comply with the Marpol Convention is only that necessary for clean ballast. Except on the last discharge before drydocking, when it is to the shipowner’s advantage to have all the tanks cleaned, the number that the shipowner will usually wish to crude oil wash is about one-third (1/3). All the tanks are washed over a cycle of three (3) trips and this is adequate to limit the undue composing of residues in the tank bottoms.
Crude Oil Washing (COW) improves the overall discharge time and any gain in the outturn quantity is to the cargo receiver’s account. Consignees obtain the maximum cargo delivery, rather than have a possible claim for short delivery. Therefore, many charterers demand that all tanks containing their cargo should be crude oil washed, which regrettably boosts the risk of a claim for short delivery on the following trip. Not all crude oils are suitable for Crude Oil Washing (COW). Some extremely heavy or waxy crude oils because of their viscous or waxy nature could increase rather than reduce the clingage.
Clean and Dirty Petroleum Products
The distinction between crude oils and petroleum products and between clean and dirty petroleum products is not as obvious as reasonably might be expected. Crude oils may be treated by adding or subtracting some components. The dividing line between a Dirty Petroleum Product and a Clean Petroleum Product is blurred. For example, gasoil falls on the dividing line. A light-colored gasoil may be regarded as a clean petroleum product whereas a dark-colored gasoil may be regarded as a dirty petroleum product and shipped on a black oil carrier. A product carrier tanker with conventional segregation can carry both clean and dirty petroleum products. Dirty Petroleum Products include Bitumen, Heavy Fuel Oils, Carbon Black Feedstock, Waxy Distillates, Diesel Oils, and Dirty Gasoil. Clean Petroleum Products include Clean Gasoils, Lubricating Oils, Kerosene, Aviation Turbine Fuel, Motor Gasoline, and Aviation Gasoline.
Heating can be a primary concern for Dirty Petroleum Products. Heavy Fuel Oils may have to be kept at a certain temperature otherwise their extremely high viscosity will cause protracted pumping time and increased outturn losses. Clean Petroleum Products require a certain level of cleanliness of the tanks, pumps, and pipelines.
Charterers of Clean Product Tankers need to know the last three (3) previous cargoes carried to ensure that the tanks can be made proper for the cargo to be loaded, for instance, that the previous cargoes were all lead-free. If heated cargo is transported in tanks next to light clean petroleum products there might be increased vapor losses and vapor pressure difficulties when discharging.
Both Clean and Dirty Petroleum Products can be carried in larger ships even VLPCs (Very Large Product Carriers) however a few charterers can find regular trade for the transportation of such vast quantities. Furthermore, consignees can only take their petroleum product parcels in amounts consistent with the size of their shore tanks.
Most of the large tankers are designed to transport Crude Oil or Dirty Petroleum Products so that they can be programmed more economically. Essentially, these tanks coated with zinc or epoxy-based materials allow the tanks to be cleaned quickly between cargoes.
It may also be required to flush the tank bottoms, gas-free, lift the scale and mop up for all Clean Petroleum Products. Furthermore, for color-critical grades flushing the tanks and lines with a proper wash may be required. Any tanker without coatings is anticipated to carry only Dirty Petroleum Products. Tank Cleaning Requirements between one grade and another must be stringently examined and all major charterers have their Cleaning Tables and Special Tank Cleaning Requirements. Different Petroleum Products have different critical properties and factors to be examined include viscosity, octane number, wax, asphaltenes, color-criticalness, flashpoint, lead-free, etc.
Chemical Tankers operate in a highly specialized trade carrying a broad range of chemicals and also a few types of other petroleum products like aromatics and unleaded gasoline. If any chemical or petroleum product cargo has a specific requirement that is not within the knowledge of the shipowner of the normal type of tanker carrying such cargoes, the charterer must advise the shipowner of the special requirements. Usually, various chemical manufacturers and chemical traders give different names for the same chemical product. Shipowner needs to know precisely what the chemical product is and not merely its brand name. A few chemical producers and a limited number of shipowners are operating chemical tankers with sophisticated tankers for carrying such chemicals. Therefore, chemical traders, producers, and shipowners have proficient knowledge and experience in their fields. Furthermore, the terminal operators handling the chemical cargoes are similarly proficient and well-equipped. Chemical Tankers are relatively small with suitable size tanks and good segregation capability. Most chemical tankers are coated with stainless steel tanks or high-tech coatings. Most chemical tankers have separate pumps and pump lines and extra safety features.
Tank Coating companies provide lists of the products and temperatures for which their coatings are suitable. If the cargo and coatings are not compatible, the cargo may damage the coatings, or the coatings contaminate or discolor the cargo. The smallest drop of some elements can throw cargo off-specification.
Liquid Gas Carriers
There are two (2) types of Liquid Gas Carriers:
- LNG (Liquid Natural Gas) Carriers
- LPG (Liquid Petroleum Gas) Carriers
There are three (3) designs of LNG (Liquid Natural Gas) Carriers:
- Moss Rosenberg Spherical Tank System
- Gaz Transport Integral Tank Systems
LNG (Liquid Natural Gas) is carried at minus 163 C (Celsius) and the boil-off gas is either used as a bunker in the main engine or put through a cryogenic plant and returned to the tanks. Shipping fleet for a gas project always has spare LNG (Liquid Natural Gas) Carrier to take into account drydocking and repairing time but if there should be an unforeseen event, it could be challenging and pricey to take replacement LNG (Liquid Natural Gas) Carrier which would be suitable for the gas project terminals. Refrigeration is the most cost-effective form of shipping for LNG (Liquid Natural Gas).
LPG (Liquid Petroleum Gas) Carriers are usually fully refrigerated but the smaller LPG (Liquid Petroleum Gas) Carriers may be part refrigerated and part pressurized. The most common LPG (Liquid Petroleum Gas) types are Butane and Propane. Butane liquefies at minus 14.5 C (Celsius) and Propane at minus 48.4 C (Celsius). PG (Liquid Petroleum Gas) Carriers may carry other cargoes besides butane and propane. The gas used for inerting the tanks of both LNG (Liquid Natural Gas)and LPG (Liquid Petroleum Gas) Carriers is nitrogen. The shore facilities may provide the initial nitrogen blanket for the cargo and this is topped up during the trip by the ship.
LNG (Liquid Natural Gas) Carriers and LPG (Liquid Petroleum Gas) Carriers have advanced instrumentation for measuring the gas tanks because it is impossible to opening the gas tanks to measure the contents. The measurement of cargo on many oil tankers is less automated and not all tankers are outfitted so that the ullages can be read in a central control room. Therefore, the deck officer in charge of loading ensures all tanks are ullaged. Ullage is the measurement of the free space above the cargo. Traditionally, ullaging is performed by using a steel tape on the end of which is a heavy calibrated brass bob. Usually, a full tank is just loaded to 98% of its capacity to allow room for cargo expansion on the sea voyage. The tanks are ullaged through the ullage openings in the deckhead. The precision of Manual or Electronic Ullaging may be affected by any movement of the tanker and any rounding off of the measurements. A tiny imprecision in ullaging a large tank can express a notable quantity of oil. Furthermore, the content of the tanks must be measured and recorded before discharge and again after discharge. Ullaging the tanks after discharge, to determine any quantities remaining in the tanks, is normally referred to as Dipping the Tanks. If charterers can not supply a Full Cargo, Dead Freight occurs. Additionally, there may be concerns about seaworthiness if the tanker has Slack Tanks. Especially, this is important with LNG (Liquid Natural Gas) Carriers and LPG (Liquid Petroleum Gas) Carriers where the surface movement of cargo in the tanks could damage their structure. LNG (Liquid Natural Gas) Carriers with partially filled spherical tanks where the surface movement can be more sweeping.
Vast amount of dry seaborne material is carried in bulk form without any bagging or packaging. Generally, such cargoes consist of one homogeneous grade, but occasionally, a vessel will carry various grades – eg: two types of coal, in separate holds; (termed “natural separation”) or, on occasions, even more than one grade in one hold. In this case cargo portions are separated either horizontally in layers by means of tarpaulins. dunnage, burlap (hessian) or by heavy-duty polythene sheeting, (although grab discharge in such circumstances will seriously increase the risk of admixture). Temporary wooden bulkheads may be used for vertical separations. Where loading and/or discharging of bulk cargo takes place at one or more berths or ports, extreme care must be taken to distribute cargo throughout a ship in a safe, seaman like fashion, enabling the vessel to remain stable throughout the voyage. A typical charter-party clause to this effect states simply: “If the vessel is destined for two or more berths and/or ports of discharge. it is agreed that the vessel be left in a safe and seaworthy condition, satisfactory to the Master, when proceeding between such berths and/or ports”. Even when loading/discharging a homogeneous cargo alongside a single berth, cargo distribution and removal must be dealt with in careful sequence, so as to avoid undue stress upon the vessel’s hull. Errors in this respect can be catastrophic and vessels have been actually broken in half because of injudicious loading. The proper handling of bulk cargo on a vessel is a skillful task and one to which even the most experienced ship’s master must carefully attend. To assist him, classification societies approve the issue to each vessel entered in their organisation of a stability booklet, specially drawn up for the ship concerned. These booklets provide guidance on loading capabilities, stability and stress in various conditions, and on commodities of varied stowage factor and peculiarity. In certain cases, United States, official loading inspectors will insist on examining a vessel’s stability booklet before permitting the ship to depart. Apart from their distribution in a ship, all commodities in bulk form have individual peculiarities, special carriage requirements, and associated difficulties. Some are particularly hazardous and advice on how they may best be transported safely at sea is given by IMO in their booklet “Solid Bulk Cargoes” – a publication necessary for every trader’s bookshelf. In addition to the risk of structural damage caused bv improper weight distribution. there exists the danger from excessive stability at the commencement of a voyage. leading to violent rolling at sea, with possible structural damage and/or shifting of cargo. Even if a ship sails with satisfactory stability, subsequent shifting of the cargo can seriously reduce stability, to the extent that, at the worst, a vessel turn over and sink. Certain bulk commodities are more liable to surface shift than others. When cargo is poured on to a nat and level (horizontal plane) surface, it will form a conical shaped heap, Assessment of the angle of repose of this heap. In accordance with methods laid down by IMO, indicate how the commodity will behave in a ship’s hold at sea. The critical angle is that of 35 degrees. Commodities with an angle of repose of 35 degrees or less (eg: bulk wheat) tend to surface movement at sea and top must be levelled off (trimmed) for safety.