This in from Wightlink, in their own words, Ed
Please remember that at 0100 hours on Sunday 31 March 2013, GMT ends and BST starts. At 0101 (GMT) all Company clocks will go forward one hour to 0201 British Summer Time (BST)
Therefore, to take account of the change to British Summer Time on Sunday 31 March, it will be necessary to amend the timetable as follows:
From Portsmouth Gunwharf: 2359 (GMT); 0300 (BST)
From Fishbourne: 0100 (GMT); 0400 (BST)
Thereafter sailings will operate as per the advertised timetable. Wightlink would like to apologise for any inconvenience that this may cause. Passengers concerned about their sailings are advised to contact Wightlink reservations on 0871 376 1000.