Very large tour vessels (those carrying more than 500 passengers) are not allowed to take passengers ashore, so their trips are known as "cruise-only".

BBC: Planning your dream Antarctic vacation

At Leith, which has a liner terminal, the length of berthing is limited, so larger ships visiting Edinburgh are required to anchor near South Queensferry and take passengers ashore by tender.

BBC: Scottish cruise passengers could hit one million

Security Council that calls for countries to "take all necessary measures ashore in Somalia, including in its airspace, " to counter piracy.

CNN: U.S. military considers options to deal with Somali pirates

CNN's Jeff Flock reported from the landing zone at Litohoro that the full force was expected take up to eight hours to come ashore.

CNN: marines