Many have wondered why HMS Queen Elizabeth has two ‘islands’. Here we consider why she is the first aircraft carrier in the world to adopt this unique arrangement and the benefits it brings. REDUNDANCY AND SEPARATION CAN BE GOOD
In a moment of inspiration back in 2001, an Royal Navy officer serving with the Thales CVF design team developing initial concepts for what became the Queen Elizabeth Class, hit upon the idea of separate islands. There are several advantages to this design but the most compelling reason for the twin islands is to space out the funnels, allowing greater separation between the engines below. Queen Elizabeth Class has duplicated main and secondary machinery in two complexes with independent uptakes and downtakes in each of the two islands. The separation provides a measure of redundancy, it increases the chances one propulsion system will remain operational in the event of action damage to the other. Gas turbine engines (situated in the sponsons directly below each island of the Queen Elizabeth Class) by their nature require larger funnels and downtakes than the diesel engines (in the bottom of the ship). The twin island design helps minimise their impact on the internal layout.
In a conventional single-island carrier design, either you have to have a very long island (like the Invincible class) which reduces flight deck space or, the exhaust trunkings have to be channelled up into a smaller space. There are limits to the angles this pipework may take which can affect the space available for the hangar. The uptakes can also create vulnerabilities, the third HMS Ark Royal was lost to a single torpedo hit in 1941, partly due to progressive engine room flooding through funnel uptakes.
The twin island design has several other benefits. Wind tunnel testing has proved that the air turbulence over the flight deck caused by the wind and the ship’s movement, is reduced by having two islands instead of one large one. Turbulent air is a hindrance to flight operations and aircraft carrier designers always have to contend with this problem. Twin islands allow greater flight deck area because the combined footprint of the two small islands is less than that of a single larger one. By having two smaller islands it allowed each to be constructed as a single block and then shipped to Rosyth to be lifted onto the hull. The forward island was built in Portsmouth and the aft island built in Glasgow.
This arrangement solves another problem by providing good separation for the main radars. The Type 1046 long range air surveillance radar is mounted forward while the TYPE 997 ARTISAN 3D medium range radar is aft. Powerful radars, even operating on different frequencies, can cause mutual interference or blind spots if the aerials are mounted too close together. Apart from a slim communications mast, both the Artisan and 1046 have clear, unobstructed arcs.
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