Michael Quinion at World Wide Words has a post on the phrase touch and go which, after explaining the obsolete sense of “dealing with some matter merely glancingly or momentarily (in the British sense of something that happens for a very short time): to merely touch on it and at once go on to something else,” goes on to the competing possibilities for the modern one (“a precarious, unpredictable or risky situation whose outcome is uncertain”):
One was given by Hotten in the first edition of his dictionary in 1859 as a coaching term: “The old jarveys [coachmen, thought to derive from the personal name Jervis], to shew their skill, used to drive against things so close as absolutely to touch, yet without injury. This they called a toucher, or, touch and go, which was hence applied to anything which was within an ace of ruin.”
The other appears in nautical contexts and was summed up by Admiral William Smyth in The Sailor’s Word-book in 1865: “Said of anything within an ace of ruin; as in rounding a ship very narrowly to escape rocks, &c, or when, under sail, she rubs against the ground with her keel, without much diminution of her velocity.” The latter sense is recorded from the beginning of the nineteenth century. One Admiralty court case in 1817 noted that a temporary touching of the keel on the sea floor “has been vulgarly described” as a touch and go, which suggests that it had even then been in the language for some time as sailors’ jargon.
Which of these is the true origin, if either, is unknowable in the present state of the etymological art. But both are based on the same idea of momentary contact that exists in the aeronautical touch and go.
My wife and I are in the middle of Patrick O’Brian’s The Thirteen-Gun Salute, where we’ve just been through a harrowing example of what Smyth describes. (Via Stan at Sentence first.)