"long enough to single up all lines"
'Single up all lines' is a common nautical term. Ships are typically moored at dock with two sets of ropes or chains, one acting as a spare in the event of a breakage. To single up all lines means to remove the redundant extra lines in order to prepare the ship for departure.
The command to single up all lines also makes an appearance in Pynchon's novels V., The Crying of Lot 49, Mason & Dixon and Against the Day. Pynchon himself served in the US Navy for a spell.