The double hulls were required on oil tankers to ensure that if the outer hull of the tanker got

ruptured ( due to reasons such as grounding, collision etc) there would be an additional layer to
ensure that the oil in the tanks did not leak out in the water.

This is already happening. Most oil tankers ( with very few exceptions) are double hulled. The
ships that are not double hulled are your bulk carriers, car carriers, passenger ships, container
vessles etc. If these ships do get ruptured in the hull, the thinks leaking out would potentially be
grain, coal, cars, people, containers respectively and these are not really pollution hazards on the
scale of a million bbls of crude oil.

So to return to your question, you seem to refer to double hull tanks as a 'security feature' . If i
am not mistaken, you actually may have wished to use 'safety feature'. But in actaul fact, double
hulls are not a safety or security ( think anti pirate measures) advantage. These are anti
pollution purpose. And this is the reason that they are used exclusively on oil tankers.

For inreasing the safety of other ships such as cruise ships the nav archs use other means such
as sub compartmentalization to ensure that if there is a breach of hill the whole ship does not
sink.

Also do remember that adding additional hull also increases the maintenance issues as the area
between the 2 hulls is narrow and not easy to maintain (chip and paint). That means it will start
rusting and affect other places.

Construction costs of double hull which is a little difficult to build are high
.

A double hull is a ship hull design and construction method where the bottom and sides of the ship
have two complete layers of watertight hull surface: one outer layer forming the normal hull of the
ship, and a second inner hull which is some distance inboard, typically by a few feet, which forms a
redundant barrier to seawater in case the outer hull is damaged and leaks.
The space between the two hulls is sometimes used for storage of ballast water.
Double hulls are a more extensive safety measure than double bottoms, which have two hull layers
only in the bottom of the ship but not the sides.
In low-energy collisions, double hulls can prevent flooding beyond the penetrated compartment. In
high-energy collisions, however, the distance to the inner hull is not sufficient and the inner
compartment is penetrated as well.
Double hulls or double bottoms have been required in all passenger ships for decades as part of
the Safety Of Life At Sea or SOLAS Convention.[1]

Oil tankers[edit]
Main article: Double-hulled tanker
Double hulls' ability to prevent or reduce oil spills led to double hulls being standardized for other
types of ships including oil tankers by the International Convention for the Prevention of Pollution
from Ships or MARPOL Convention. A double hull does not protect against major, high-energy
collisions or groundings which cause the majority of oil pollution, despite this being the reason that
the double hull was mandated by United States legislation.[2] After the Exxon Valdez oil spill disaster,
when that ship grounded on Bligh Reef outside the port of Valdez, Alaska, the US Government
required all new oil tankers built for use between US ports to be equipped with a full double hull.

Submarines[edit]
In submarine hulls, the double hull structure is significantly different, consisting of an outer light hull
and inner pressure hull, with the outer hull intended more to provide a hydrodynamic shape for the
submarine than the cylindrical inner pressure hull. In addition to tailoring the flow of water around the
submarine (also known as hydrodynamic bypass), this outer skin serves as a mounting point
for anechoic tiles, which are designed specifically to absorb sound rather than reflect it, helping to
hide the vessel from sonar detection.

A double bottom is a ship hull design and construction method where the bottom of the ship has
two complete layers of watertight hull surface: one outer layer forming the normal hull of the ship,
and a second inner hull which is somewhat higher in the ship, perhaps a few feet, which forms a
redundant barrier to seawater in case the outer hull is damaged and leaks
An even more extensive protection is available as a double hull, where the second hull layer extends
up the sides of the ship as well as in the bottom.