Nick Hancock, 39, hopes to spend 60 days on the extinct volcano 260 miles west of the Outer Hebrides.
A previous attempt last year ended after rough seas prevented him from landing.
The current occupation record is 42 days, which was set by three Greenpeace campaigners in 1997. The 40-day solo record was set in 1985 by the SAS veteran Tom McClean.
Mr Hancock, a chartered surveyor based in Edinburgh, left Leverburgh in South Harris yesterday afternoon on motor cruise boat Orca III, bound for the remote outcrop, under the command of experienced yacht skipper Angus Smith.
They hope to arrive at the rock this morning and Captain Smith will make the decision whether or not it is safe for the adventurer to attempt a landing.
If he lands he will have to single-handedly haul his converted water tank, communications and cooking equipment and supplies for at least two months up the steep slippery rocks. While there, he will live in the converted eight-foot water tank.