It is urging inexperienced boaters not to cross the channel through sailing clubs and local, regional, national and specialist press.
Geldof has called for people to 'recreate Dunkirk' by sailing across the channel and picking up French supporters of the Live 8 event.
Sail 8, which is supported by yachtswoman Ellen McArthur, has also called on French owners of small boats to make the crossing and travel to Edinburgh in the run-up to the G8 summit.
'The danger is that people will sail in inappropriate craft,' said Kinross & Render CEO Sarah Render, who is leading the anti-Sail 8 campaign. 'They could be inexperienced sailors taking their whole families without the experience to dodge large ships.'
She added that contrary to some media reports, the channel will not close to commercial vessels.