The couple were keen to marry at their French estate Chateau Miraval later this summer, but have changed their minds thanks to their son Maddox, 11. They are now looking to get married on the cruise ship, which sails across the Scottish Isles, reported Sun online.
"It was Maddox who came up with the idea of the ship. He came across it after looking back at photos of the Carnell Estate in Ayrshire, where they stayed and all loved," a source said.
"So now they've made enquiries into booking the whole vessel. It's just what they're after. It can hold up to 50 of their friends and family and serve as a traditional, romantic setting -- all totally private.
"Or they could always sail to a secluded bay off the Orkney or Shetland islands and have the ceremony there. The fact that Maddox found it makes it more special," the source added.
The luxury ship has been used by the British Monarch on two occasions - in 2006 to celebrate her 80th birthday and again in 2010 for a family holiday.