In this context, to "jump" implies one thing: to attempt escape. For this prison is different from others - the Vernon C Bain is a prison barge or, as the New York City Correction Department prefers to call it, a "floating detention facility". In the three-year life of the Bain only one inmate has made such an attempt: he could not swim and was quickly retrieved.
Docked on a bleak promontory of warehouses and sewage plants in the South Bronx, the Bain has suddenly become the object of much British interest. Another on-board tour was given recently to visiting officers from the British prison service. They, like us, wanted to explore the practicality of a place like this and for a very urgent reason: Britain is negotiating to buy another such barge once operated by New York, though no longer in operation.
That barge is called the Resolution. Considerably smaller than the Bain - and assuredly less impressive - its life-story includes a stint as a barracks for British soldiers in the Falklands in the aftermath of the conflict there. It and a sister ship, the Venture, were purchased by New York in 1987 when the city's own prisons were overfilled to bursting point. Originally moored at piers on different sides of Lower Manhattan, they were abandoned by the prison service in 1992 and sold to a European line in 1994.
Faced with its own overcrowding crisis now, the Government has a simple plan: to buy the Resolution, plop it into a much bigger, ocean-going barge and bring it across the Atlantic. Negotiations for the purchase are contingent on planning permission being granted by the city council of Weymouth, where it would be docked - a planning hearing is scheduled for 5 February. Just conceivably, the Resolution could be docked and ready by April. An alternative prison barge in Denmark is also being considered.
The image of prison ships as floating hellholes comes, in part, from history that was made right here in New York - by the British. During the American Revolution, multitudes of captured soldiers were incarcerated aboard the Jersey and other creaking British naval ships moored in the Wallabout dock area of Brooklyn. The unfortunate Americans were allowed gently to rot and more than 11,000 expired.
Their tour on the Bain, at least, must have left the British officials encouraged. Purpose-built in New Orleans at a cost of $161m (almost pounds 100m ) and put into service in 1992, the Bain rises high above its dock and, painted white and blue, looks much like a smart industrial plant. It can accommodate 800 inmates in a degree of comfort not offered by most American jails on land. Dressed in their own casual clothes, most are on board short-term - either awaiting trial or transfer to a land facility elsewhere.
Inside the Bain, it is easy to forget you are on water. It rocks only occasionally when other large ships pass by, explains its deputy warden, Tom Minti. "I always say to people that if I was to take you on here blindfolded, you would never know you were on water." There are reminders, however: the entire structure is steel, and occasionally you feel the vibrations from the internal heating and air-conditioning systems. (It has no engines.) Everywhere there is pale linoleum, except inside the mosque on the bottom deck, which is carpeted. The chapel, next door, has lino and a wooden altar.
Among the officers, the efficiency of the Bain evokes obvious pride. Once an officer on the Resolution and now on the Bain, Captain Tom McCann (the rank is a prison one, with no maritime significance) is happy it is not the Bain that is for sale. "Send this to England and I'm going with it," he says. After shooing us out to the open exercise yard, with stunning views south to Manhattan obscured only by 15ft fencing topped with razor-wire, he shows off the inside gym - a space that would be the envy of most schools.
Nor, it seems, does operating a prison on water present any particular problems. Coast Guard rules require permanent residence by a ship's mate, an oiler and a ship's engineer. Occasionally, divers are sent below to scrape barnacles from the hull. And the Bain's record of only one escape attempt (failed) suggests no special security problems. "There is no difficulty," explains Mr McCann. "If you like, we have the advantage of a natural barrier of water that goes back to ancient times of castles with moats. Inside, our procedures are no different to any other prison."
The British may have been distinctly less taken by the Resolution, however. Unfortunately, perhaps, it is moored now at a remote quayside in Brooklyn not far from the infamous waters at Wallabout. As well as being much smaller than the Bain - its capacity is for only 384 inmates - it was not built to hold prisoners. Painted in a uniform navy grey, it has the appearance of a flat barge with five layers of Portakabins piled on top of one another. Accommodation is in two- man cells with strip lights and spartan wooden bunks. The outdoor exercise area, by comparison with the Bain, is tiny.
Nor apparently, is it in anything like such good shape. Our brief foray aboard the Resolution, (before being swiftly ejected by a gentleman who was less than delighted to see us) revealed workers toiling with steel plates to patch up areas of the main deck that had rusted all the way through. One corner is stacked high with cases of Rust-Oleum, an anti- oxidant treatment.
Apparently, then, work on renovating the Resolution has already begun. The cost of the repairs, of its transport across the ocean and of the preparation of a secure dock at Weymouth is likely to be very considerable. And should it eventually arrive in Britain, it will hardly be as salubrious as the Bain. But, if it's any consolation to prospective inmates, nor will it offer any of the gruesomeness to be found aboard the Jersey more than 200 years ago.