The hull of the ship is the outer skin of the vessel which ensures there is no water ingress inside it và ensures the watertight integrity of the ship khổng lồ maintain its floating status. 

The outer skin known as the hull of the ship can be of a single layer or of double-layer, i.e. there are two hulls of the ship known as double hull. The double hull is most commonly found in oil tanker ships. 

The International Maritime Organisation (IMO) introduced the regulation 13 F of Annex 1 of MARPOL, which effectively mandated double hulls for newly built oil tankers of 5000 deadweight tonnage & above sầu. The Exxon Valdez oil spill disaster also led the U.S. Government to lớn make double hulls compulsory for all new tanker ships coming khổng lồ the U.S. ports. After the sinking of vessel Erika off the coast of France on December 1999, IMO proposed accelerating phase-out of single-hull ships.

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The hull separation distance between the two layers of the double hull was determined by surveying the penetration depths in numerous accidents. OPA 90 provides the details of the separation distance which should be lesser of: 

* B/15 or at a minimum, 1.0 meters; or 

* 2.0 meters

where B is the beam or width of the vessel 

The double side tanks require a minimum width of two meters.

However, passenger ships are also provided with double skin as per the SOLAS under Chapter II-1: Construction – Structure, subdivision và stability, machinery & electrical installations, Regulation 12.

Related Read: SOLAS and MARPOL 

The submarines also have sầu a double hull. However, the purpose of the double skin is for different use. The details about the  Design of a Submarine can be read in our article-.Structure Design of a Submarine. 

As the oil carries dangerous & pollutant cargo in fluid form, the double skin of oil tanker is very crucial. 

Double hull, as mentioned earlier, are tanker ship hulls with double layers of the watertight hull surface. The inner & outer layers of the hull are on the bottom as well as the sides of the tanker ships. The double-layer construction helps in reducing the risks of marine pollution during a collision, grounding, và any other khung of ship’s hull damage. It also saves the ship from water ingress or flooding if the outer layer fails.

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Thus double hull ships are more susceptible to lớn minor structural failures as compared to the single hull tankers. This can also be a matter of concern during accidents which cause oil spill as a result of structural failure.

Ventilation is of utmost importance in double bottom tanks of double-hull tankers as they need an inspection from time lớn time. As double bottom tanks are không lấy phí from any internal structure, it is easy to lớn access them. However, they are not so friendly when it comes khổng lồ close-up inspection, or accessing side tanks or deckhead areas; whereas though tanks of the single-hull are difficult to access, their confined areas much more ‘inspection friendly.’

Related Read: Procedure for Entering an Enclosed Space on a Ship

The average time taken for a discharge operation in oil tanker is less in double-hull tanker as compare to lớn a single hull tanker ship và the cargo remaining onboard post completion of the discharged cargo is also less in double-hull tanker ships. 

The cleaning of cargo tanks in double-hull tanker ships is easier & faster. The reason behind it that most of the vessel’s cargo tank framing is located in the ballast tanks, leaving smooth surfaces in the cargo tanks. 

As of today, no single-hull oil tanker ships are carrying heavy grade oil cargo are in operation since năm ngoái. 

Double-Hulled Fuel Tanks

To enhance the safety of the ship and to lớn avoid oil pollution for all type of vessel carrying oil as a fuel, the IMO has adopted a regulation under MARPOL Annex 1 that requires all types of ship with an oil fuel capađô thị of 600m3 và above sầu to have the fuel tanks area double-hulled. This rule came in 2007 and all ships with building contract placed on or after August 1, 2007, or with keel laid on or after February 1, 2008, must have sầu double hull fuel tanks. 

Related Read: Procedure for Cleaning Fuel Oil Tanks on a Ship

Additionally, all vessels delivered after August 1, 2010, must comply with this regulation. 

All vessels delivered on or after August 1, 2010; và,All vessels having undergone a major conversion completed on or after August 1, 2010.

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Under this regulation, the fuel oil tank with a capađô thị of 2,500 m3 is also included. This new regulation intends khổng lồ require the same standard of safety và pollution prevention from fuel tanks as is needed for cargo tanks in oil tankers. It is assumed that all of the cargo ships will have double-hulled fuel tanks by 2040. 

Disclaimer: The authors’ views expressed in this article bởi vì not necessarily reflect the views of Marine Insight. Data and charts, if used, in the article have been sourced from available information and have not been authenticated by any statutory authority. The author and Marine Insight bởi vì not clayên it to lớn be accurate nor accept any responsibility for the same. The views constitute only the opinions and vì chưng not constitute any guidelines or recommendation on any course of action khổng lồ be followed by the reader.

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