The four-day event, which previously has been held in Portsmouth (twice) and Bristol, costs pound;2 million to stage and takes 18 months to set up, says one of the directors, Annie Taylor. She, like most of her colleagues, has strong connections with the sea. The team's most experienced sailor is Sue McKichan, who has navigated Cape Horn.
"Britain is an island and the sea makes a powerful contribution to our lives," says Ms Taylor. "The sea isn't just about what floats on it. It's also about what lives in it, the industries connected to it, traditional marine skills and so on. The festival was founded to celebrate all those things and to educate the public at the same time.
"By holding the festival in Leith, we can draw attention to the Firth of Forth and encourage schools throughout Scotland to focus on their maritime heritage."
The festival will offer plenty of things to do and see. Visitors will be able to climb on board and speak to the crews of some of the 150 spectacular vessels tied up at the harbour, including a unique replica of a Highland galley.
A model boat exhibition will include a world-renowned Scottish fleet of 200 warships made entirely from matchsticks and match boxes.
Try diving, or find out what it feels like to go into the control room of a submarine or on a Merlin helicopter flight. There will be air-sea rescue displays with helicopters and lifeboats and demonstrations by parachute and commando teams.
Learn about the maritime history of Scotland and how ropes are made, knots are tied and boats are built. Watch fish being landed at the quayside and then processed in a traditional Norwegian smoke house.
Deep Sea World is bringing a mobile pool and a 100ft inflatable blue whale.
Sandcastle building will, hopefully, be taken to a new level with the construction of the biggest sand sculpture in the UK.
Granton Primary, in Edinburgh, is one of several schools taking part in the festival's twice-daily parade, which will feature famous Scottish characters with seafaring connections. The school's choir will also be performing.