The ship's crown is her funnel. It is one of the most distinctive features of any vessel and it has to be both functional and, at the same time, stylish and striking.

Oceana and Adonia both have a sweeping, curved funnel that fits the overall appearance of the vessels and also hides the collection of essential pipes from the ships' many systems and equipment.

On the White Sisters, the funnels also hide a secret, as they are big enough to house the vessels' sports deck, which includes a tennis, basketball and volleyball court in the base of the buff-coloured structure.

A P&O spokesman in Southampton said: "Typically these pipes will come from the engines, incinerators, boilers and galley air extraction systems.

"On a cargo ship the funnel will tend to be a simple affair as all it needs to do is carry the pipes skyward to a height where the exhaust can be most effectively dispersed, but on a cruise ship the funnel has another role to play. "Take a look at a range of cruise liners and you will see funnels of all shapes, colours and sizes. In this market, the funnel is often used to create a distinctive identity for the ship, clearly identifying the company to which the ship belongs.

"The funnels of P&O Cruises are painted in an unmistakable buff yellow colour, while those of other companies have characteristic shapes or display the company logo or name.'' The size of Oceana's and Adonia's funnels is remarkable and gave designers serious challenges as they were transformed from blueprints to reality.

Firstly the funnels had to fit in with the overall sleek appearance of the ships but such a large structure could create a disturbance in the airflow over the vessels.

In the end the answer was the result of close co-operation between the marine engineer, exterior designer and naval architect.

"The marine engineer developed an exhaust pipe arrangement that allowed the exterior designer to create a large open area for the sports deck,'' said the P&O spokesman.

"The exterior designer developed the arched funnel shape and in turn worked alongside the naval architect to work out the air flow.

"Together they created the slatted faade that allows air to pass through the funnel calmly and minimises turbulence in the exhaust and on the adjacent decks.''