The propulsion on a cruise ship is the engines which are Diesel Electric Propulsion systems.
The main engines on cruise ships are generators which make electricity and in turn powers the azipods.
Cruise ships typically have 4 engines and 2 azipods and 3 bow thrusters that provide the ship with maneuverability when departing and arriving at a port.
Some ships propulsion systems consist of either one or two propeller shafts each with its own direct drive engine.
Ships propelled by medium or high speed diesel engines may have one or two (sometimes more) propellers, commonly with one or more engines driving each propeller shaft through a gearbox.
Cruise ships are typically in port for nine or 10 hours while they exchange passengers and reprovision.
Their huge diesel engines, powering everything from their lights to air conditioning, run the whole time and emit exhaust leads to air pollution.
The dirtiest cruise ship is the Oceania Insignia as well as the Silver Spirit, Silver Wind, Safari Endeavor, Norwegian Breakaway and Le Boreal.
The cleanest cruise ships are Carnival Cruise Ships and Royal Cruise Ships.
Cruise ships do not put laxatives in food as that would cause legal action and bad press.
Some people may get sick from being on a cruise ship or from eating foods that may have been bad but it's rare for the food to cause food poisoning on a cruise ship.
Some people also become sick to their stomach from the cruise ship itself being on the water and they may think it's from the food they've eaten.
Organisms such as salmonella, shigella and E. coli have caused outbreaks of diarrhea on ships, and fall into the grab-bag category of "traveler's diarrhea."
In a recent cluster of gastrointestinal illnesses on a cruise ship sailing from Tenerife to the U.S., salmonella was identified as the likely culprit.
In the U.S., the risk of getting norovirus each year is about 1 in 15; a cruise passenger has about a 1 in 5,500 risk of getting laboratory-confirmed norovirus during a shipboard outbreak.
Food poisoning is common on cruise ships because of the close proximity and buffet-style dining on cruise ships are sometimes a perfect recipe for foodborne illness from both bacterial and viral pathogens to spread much more quickly than we typically see at home.