Types of Ships

Mail and Supply Ships

These ships carry mail, supplies and also general cargo to out-of the way destinations. They basically connect small isolated communities. These ships generally have provision for accommodation which is higher than a usual freighter.

For example the “Aranui 3” is a ship which belongs to this category which departs Tahiti about 16 times a year, connecting the remote islands of Tuamotu and Marquesas of French Polynesia in South Pacific. This is a cargo ship which has been built with passenger comfort in mind; offers tastefully decorated spacious accommodations and provide recreational facilities as swimming pool, gym, scuba diving and snorkelling etc.

Expedition Ships

These ships are usually small for flexibility and ease of manoeuvrability in navigating through uncharted areas. These ships may have special purpose equipments installed to meet specific requirements of the expedition like prolonged sailing in high latitudes. Other than scientific research purposes, these ships are also used for adventure tourism.

Coasters

These are small cargo ships running on feeder routes. They usually transport the cargo to (from) different locations which are transhipped from (to) large container ships.

They are usually shallow hulled for plying in lower draft waterways.

Bulk carriers

These are large single deck vessels and their cargo usually comprises of coal, mineral ores, food grains and other produces. Basically they handle all types of bulk cargo which cannot be containerized.

The different sizes of bulk carriers are:

• Mini bulkers :           Under 10,000 DWT
• Handy size :           10,000 to 35,000 DWT
• Handymax :           35,000 to 60,000 DWT
• Panamax :           60,000 to 80,000 DWT
• Cape size :           80,000 and over DWT

Mini bulkers have single holds and are designed for river transport.

Handy size and Handymax are general purpose in nature.

Panama ships are those which can pass through the Panama Canal.

Capesize ships cannot pass through the Panama Canal and have to travel around Cape Horn while travelling between Pacific and Atlantic Ocean.

For loading and unloading of bulk cargo sometimes the ships have necessary cranes and other material handling facilities and are known as “geared” bulk carriers. However they usually do not have such facilities and are referred to as “gearless” bulk carriers.

As bulk cargo can be very abrasive and corrosive, they affect the life of bulk carriers leading to higher risk of operations. New regulations have been introduced to improve ships design, inspection and the process of abandoning to reduce the hazards in operations.

Tankers

Tankers have on board facility for oil pumping, heating and certain other special provisions. A tanker generally sticks to a single product. According to the type of cargo, they are further classified into.

• Oil tankers: These are bulk ships dedicated to the transport of unrefined oil. These are largest ships in the world and are further classified as:
• Up to 80,000DWT : Afframax
• Up to 300,000 DWT : VLCC (very large crude carriers)
• Beyond 300,000 DWT : ULCC (ultra large crude carriers)

VLCC and ULCC are very large vessels and can call on a few ports in the world because of the draft required. Usually a VLCC or ULCC does not enter a port but stay outside the port in deep waters from where the oil cargo is transferred through smaller crude carriers.

• Product tankers: Product carriers transport refined products as gasoline, diesel oil or others refined products. The vessel may carry up to six different products of the piping and other facilities are available for proper segregation. These vessels are in the range of 1000- 60,000 DWT.
• LNG tankers: LNG tankers are specially designed to carry Liquefied Natural Gas. In recent years there has been increase in the number of such vessels around the world.
• Acid tankers: Acid and chemical tankers are those which carry in bulk products listed in Chapter 17 of the International Bulk Chemical Code. The tanks are designed to ensure safe transport of liquid products of corrosive nature and are usually made.
• Edible oil tankers: Edible oil tankers are a form of acid or chemical tankers which carry vegetable oils. Their tankers are specially designed with epoxy coating.

Refrigerated Vessels or Reefers

These ships are used for transporting perishable goods as fruits, meat, fish, vegetables, dairy products and other foodstuffs. These ships can keep the cargo under controlled temperature.

This category of ships is further classified as.

• Side door vessels: the sides are lowered to serve as loading and discharging ramps for the forklifts. This type is particularly designed for short distance trade.
• Conventional reefer vessels: they have traditional cranes suitable for handling of palletized cargo.

To prevent decomposition refrigeration is applied to the goods. As a consequence of technological advances these ships have “inert atmosphere” in the holds also known as “Controlled Atmosphere”.

Each cargo carrying space is lined by layers of insulation material. The floor is also double skinned with gratings with precisely measured air passage openings to maintain even circulation of cooling air. The temperature is usually in the range of -30 to 12◦ C depending on the cargo.

The cargo maybe carried loose or in individual boxes or pallets.

These ships operate at higher cruising speeds of 18-23 knots to reduce the carriage times of perishable items.

Livestock Carriers

These ships have provisions to exclusively transport large number of line animals which are mostly domestic breeds of sheep and cattle.

The types of livestock carriers are.

• Open livestock carriers: On these ships the animal pens are installed on open decks. This reduces the reliance on mechanical ventilation system. However as wind speed would greatly influence the ventilation level in these pens, supplementary mechanised ventilation is also available.
• Closed livestock carriers: In this type of ships, controlled environment is provided to the animals and they are also protected from adverse weather conditions.

LNG Carriers

As already explained LNG tankers are specially designed to carry Liquefied Natural Gas.

LNG Tankers have a capacity of up to 140,000m3, but larger vessels with a capacity of 200,000m3 or more are under development.

Safe transportation of LNG is paramount therefore the carriers that transport it have.

• Double-hull specifically designed to handle the low temperature of LNG and provides protection for cargo in the event of a collision, grounding, and from radiant heat.
• Cargo tanks are located away from the hull.
• Gas detectors and safety alarms situated between the steel hulls which and continuously monitor for cargo leaks.

In a typical cargo cycle, the tankers are first filled with inert gas using the inert gas plant which burns diesel to replace the oxygen in the tanks with carbon-dioxide. This reduces the explosive atmosphere in the tanks.

While loading, the LNG is initially warmed up and blown into the tanks to displace the “inert gas”. After the tanks are free of inert gas, they are colled down to about -150◦   and loading takes place.

Car Carriers

These are basically Ro-Ro type of ships which have large rectangular design and are purpose built to carry large number of cars. These are also known as PCC (Pure Car Carrier) or PC/TC (Pure Car/ Truck Carrier)

On these ships, the cargo capacity is often measured in RT or RT43 units who are based on a 1966 Toyota or by car equivalent units (CEU).

Manufacturers of cars, mainly in Japan, Korea and Europe, use these vessels to ship large quantities of their products around the world. Every Japanese, Korean car one comes across in Europe may have been brought across on one of these car carrier vessels.

Lately with the sinking of few such ships, criticisms have started on the inherent weakness in the design of such vessels with a single massive hold. In case water gets into the hold, with no watertight bulkheads and the free surface effect of that, water rapidly de-stabilises the whole vessel and in a matter of seconds they can capsize.

Container Ships

The most popular method of transporting goods by sea is the container ship. Containers come in standard 20 foot and 40 foot sizes, which means that ships can be loaded and unloaded very quickly – and time is valuable for the shipping lines.

A ships container capacity will be described as so many TEU – this stands for ‘twenty foot equivalent units’. Therefore, if a ship could carry 1000 forty foot containers, that is the equivalent of 2000 twenty foot containers – meaning its capacity is 2000 TEU.

Modern container ships are fast – they can cross the Atlantic in as little as 7 days – and the largest ones are so huge that you get a very smooth ride in all but the roughest conditions. These are factors that may be considered an advantage by some people.

Heavy Lift Vessels

The heavy lift ships are designed to carry excessively large loads that even cargo ships cannot bear, such as other ships, drilling rigs or anything else too large or heavy to be easily transported on a conventional ship.

A particular feature of heavy lift ships is the semi-submergence capability for lifting another ship out of the water and transporting it. Semi-submerging vessels are also known as a “flo/flo” (float-on/float-off).

These vessels have a long and low well decks that can go down under water allowing oil platforms, other vessels, or other floating cargo to be moved into position for loading. The tanks are then pumped out, and the well deck rises higher in the water, lifting its cargo, and is ready to sail wherever in the world the cargo needs to be transported.

The flo/flo industry’s largest customer base is the oil industry. They have transported many oil drilling rigs from their construction site to the drilling site at roughly three to four times the speed of a self-deploying rig.

Tugs

The name Tug Boats gives a fair idea about the size and task of the vessel being discussed.

Tugs or Tug Boats are relatively smaller but very powerful for their size. These are primarily used to tug or pull vessels that cannot move on their own like disabled ships, oil platforms and barges or those that should not move like a big or loaded ship in a narrow canal or a crowded harbour. In addition to these, tug boats are also used as ice breakers or salvage boats and as they are built with fire fighting guns and monitors, they assist in the fire fighting duties especially at harbours and when required even at sea.

Ro-Ro Vessels

Ro-Ro is an acronym for Roll-on/roll-off ships which are used to carry wheeled cargo. The Ro-Ro ship is different from Lo-Lo (lift on-lift off) ship that uses cranes to load the cargo.

The vehicles in the ship are loaded and unloaded by means of built-in ramps. Consequently they are like ferries but much larger and have multiple decks to carry thousands of vehicles. Normally these ramps are made towards the stern (backside) of the ship. In some ships, they are also found on the bow side (front) as well as the sides. The vessel can be of both military and civilian types.

In the shipping industry usually the cargo is measured by the metric tonne, but Ro-Ro cargo is typically measured in units of ‘lanes in metres’ (LIMs). This is calculated by multiplying cargo length in metres by the number of decks and by its width in lanes (lane width differs from vessel to vessel and there are several industry standards).

These are mainly utilised by vehicle manufacturers to transport their products across the world.