What are the silver cylinders near the smokestack on the Island Princess cruise ship. ?

Here is a photo of the Diamond Princess and you can see the two horizontally mounted silver cylinders that look like jet engines …

http://i18.photobucket.com/albums/b103/ZefH/Diamond%20Princess/Diamondleaving.jpg

The Princess ships that have these actually do have a jet engine used to help power the ship. The ship’s engines don’t actually turn the propellers, but rather create electricity that is used to power the electrical motor that actually does turn the propellers.

Here is some more information on the Diamond Princess’ engines …

The Diamond Princess differs from existing passenger ships, first of all, in the fact that when cruising it uses a diesel engine and when moving at high speed it employs a CODAG-configuration power system, which combines the diesel engine and a gas turbine. While providing strong output, the gas turbine, which utilizes airplane technology, produces little noise and little vibration. Though rooms right above the propeller would normally be quite noisy and subject to vibration, it would be possible to put luxury suites in this location on the Diamond Princess. At the same time, the positioning of the gas turbine behind the funnel gives the ship more inner space.

http://web-japan.org/trends/science/sci040407.html

Here is some more information …

Diamond Princess has an instantly recognizable funnel due to two jet engine-like pods that sit high up on its structure but really are mainly for decoration.
…

Diamond Princess is the first of the “Grand Class” ships to have a “pod” propulsion system installed. Electrical power is provided by a combination of four diesel and one gas turbine (CODAG) unit; the diesel engines are located in the engine room, while the gas turbine unit is located in the ship’s funnel housing, on each side of which is a cosmetic pod that resembles a jet aircraft engine.

http://www.cruise.co.uk/cruises/38/Diamond-Princess/