What are Double Hulls for Ships?

A double hull ship is a type of a ship that has two levels or layers of hulls – the outer layer and the inner layer. The double hulls are an important requirement in ships, especially oil tankers. The reasons why they are important, the benefits of having double hull tankers and the disadvantages are explained in details in the article.

The system of the double hulls works in such a way that on the sides and the bottom of the ship, there are two layers with empty space between these layers. Because of the two layers of hulls, any loss to the ship’s cargo while accidents occur, are highly minimised. If one layer is damaged due to collision or similar accident, the second layer acts as a back-up and prevents ingress of seawater into the ship. Also, the loss to the cargo is restricted only to a certain portion of the double hulled ship unlike the single hulled varieties.

Since there is a gap between the outer layer of the hull and the inner layer, ballast water is used to store in these empty spaces on both – on the sides and on the bottom of the ship. Sometimes, even fuel is used to store in this empty area.

The usage of double hulls in oil tankers was recommended in the MARPOL (International Convention for the Prevention of Pollution from Ships) convention. This recommendation came after observing its advantages when used in passenger ships which have been recommended to have double hulls as per the SOLAS (Safety of Life at Sea) meet or convention.

The need for double hull oil tankers was felt even more after the Exxon Valdez casualty that occurred in 1989. But, even though double hulls are quite efficient when it comes to protecting the tankers, in case of major accidents and collisions they can be quite ineffective. This is one of the major disadvantages of having double hull tankers.

The second-most important and noticeable disadvantage of having double hulls is that the ship tends to be unstable sometimes. This is because of the two layers of the hulls that displace the centre of gravity of the ship. These two factors act as a major negating factor about the usage of double hull tankers.


The maintenance of the double hull ships is also very important. The double hulls are very prone to erosion making it very necessary for the personnel on the ship to pay extra attention to the condition of the tanker. If the ship’s condition is not monitored carefully, then even in spite of the double hulls there could be a major loss to the tanker.

Double hull tankers have their own positives and negatives. But even though they lack in many areas, it cannot be denied that in the present-day marine cargo transportation, they offer the best possible services as far as the safety of vessels is concerned. This service providing is what that makes them so unique.

You may also like to read-What are Panamax and Aframax Tankers?Tanker Ship Triality

 

References:

wisegeek

seas-at-risk

amsa

image Credits:

schleswig-holstein

nassco

 

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