When two running ships collide head to head, there is no doubt that severe structural damage will occur. Even after such collision the vessel should not have sunk and so many passengers should not have died if it had been designed to the required standard and appropriate safety rules were followed. I do not know how many life-jackets the vessel was carrying, when every passenger must have one.
Compartmentalisation is a basic design criterion to prevent the ship from sinking in case of collision or grounding. In the event of an accident, the water-tight part is still available to provide buoyancy to keep the vessel afloat. Reserve buoyancy available will depend on how the hull (body) is divided into separate watertight compartments. It should be divided into many parts so that a single collision on one spot can't damage all the watertight compartments.
A floating football will not sink until it is pierced, allowing some water to ingress inside the ball. Similarly, a ship can be prevented from sinking if its watertight integrity is maintained. According to the law of Archimedes the ball will sink when the weight of the ball and the water inside it is greater than the weight of the water displaced by the football.
Watertight integrity of a ship may be broken when a ship collides with other vessel or any underwater object. A vigilant watch by well trained and certified navigators and electronic watch by the modern radars help prevent collision. Watertight integrity may also be broken if a ship's side or bottom develops a hole due to ageing or quality of steel. Periodical tank inspections and underwater survey give early indication of material failure. The thickness of the steel plates is measured by ultrasonic gauging, and reduction of thickness from the original thickness can be detected. This method is used by all the regulatory bodies to make the renewal of plates obligatory for the owners at about 20% to 30% reduction of the original thickness. Accordingly, the owners renew steel plates to protect a vessel from any possible damage due to worn-out steel structure.
A ship is not as watertight as a football. It has got many openings on its weather deck that are prone to water ingression in case of unsafe loading, rough weather, as well as in case of bad design. Due to violent external force a ship will roll and pitch and frequent immersion of the deck may occur. During this period, sweeping water will try to ingress through various openings on deck, such as doors of accommodation, machinery space openings, ventilators, port holes (accommodation windows), side scuttles, sounding pipes of fuel or ballast tanks, etc. If all openings are designed and maintained properly the ship will remain watertight, uphold its stability and will not sink even in bad weather .
However, to prevent water ingression through different openings on deck water has to be kept at a distance from the deck. This distance is called "Freeboard" and is well known in the maritime industry. The first seafarers who set to sea in wooden canoes thousands of years ago must have already -- perhaps by trial and error -- worked out the optimum freeboard for those vessels.
The minimum freeboard is designed to provide a standard of "reserve buoyancy" (the volume of the watertight hull above the load waterline), while the protection of openings in the hull and superstructures, such as hatches (opening of cargo spaces), ventilators, air-pipes, scuppers (drain pipes), and the access openings in accommodation, is an important consideration in the assignment of freeboard. Freeboard is assigned to every individual ship by the state administration.
Freeboard is measured from the top of the deck amidships to the top of the line through the centre of the load water-line disc (a circular ring painted on a ship's side). Forward of the disc is a grid composed of lines indicating the maximum loading -- at the level with the line in the disc for the summer and others further down for winter in the north Atlantic, and above for the tropical zones and for fresh water. Here is a picture to show the freeboard markings on a British cargo vessel:
The first 19th century loading recommendations were introduced by London-based Lloyd's Register of British and Foreign Shipping in 1835, following discussions between ship-owners, shippers and underwriters. Lloyd's Register recommended freeboards as a function of the depth of the cargo hold (three inches per foot of depth) and these recommendations, used extensively until 1880, are known as "Lloyd's Rule". However, the Rule applied only to ships registered with Lloyd's.
In the year 1873-4, around the coastline of the United Kingdom, 411 ships sank, with the loss of 506 lives. But this figure only covers the United Kingdom coastline: between 1867 and 1882, loss of life in British vessels alone (excluding fishing vessels) totaled 33,427 seafarers and 5,987 passengers. Ships lost numbered 16,393.
In 1906, laws were passed requiring foreign ships visiting British ports to be marked with a load line, while a German law of 1903 also issued freeboard regulations, spreading the regulatory net further.
From the history of load line markings, we can see the significance of assigning the markings by the administration and maintaining the markings during operation. All assigned load lines must be marked amidships on each side of the ship, and must be clearly visible to the safety inspector.
We may have to review our national standard of construction of vessels, supervision of operational load lines as well as the assignment of freeboards to the vessels, taking into account the seasons as well as the type of cargo -- passenger, oil, dry cargo, etc.
Many incidents of sinking passenger vessels that cost thousands of innocent lives must have stirred the people's hearts, and they now demand corrective measures from the government. The root causes of the incidents have to also be found.
It is shocking to see lifeless bodies floating without any life-jacket, a safety gear that must not be ignored by the ship owners and ship inspectors anymore.

The writer is Engineer Surveyor, International Ship's Classification Society.