One reason for comparing a seaplane with a boat is that both called the sea their home. The Goose lives on the west coast of the US, where it is a tourist attraction. Prelude currently lives somewhere in a South Korea shipyard but will soon be heading for west coast of Australia.

Another reason is that both have (or had, in the case of the seaplane) the potential to rewrite history by (a) changing the business of heavy-lift air cargo and (b) changing the business of LNG production.

The common thread is that the people behind both engineering marvels reckoned that size really does matter when it comes to efficiency and, potentially, to profit.

In the case of the Goose, also known as the flying timber-yard because it was built of wood, no-one will ever know because after its first (and only) test flight of about 1.5km on November 2, 1947, the aviation monster was mothballed and consigned to a museum.

Sometime this year, 70 years after the Goose made headlines, Prelude should start producing LNG from one of the loneliest gasfields in the world, located 475km north-east of the Western Australian tourist town of Broome.

It is highly unlikely that Prelude, a venture led by Shell, will end its life in a tourist museum.

Yet it is possible that Prelude will perform a little like the Goose in that it will prove the concept of FLNG in the same way the aircraft proved the concept of a giant seaplane, with few followers willing to tackle the financial challenge of making money from producing LNG on a barge in the middle of the ocean.

The eight-engined Goose, with a wing span wider than an Airbus A380, died for a number of reasons. Cost was one of them.

The end of the Second World War was another with the need for a giant aircraft to protect convoys across the Atlantic causing the cancellation of the project which had been led by the legendary Howard Hughes, whose fortune was based on the tri-cone oil-drilling bit patented by the Hughes Tool Company.

Prelude is very much alive and is a project being watched closely by the oil world because while it is not the first floating LNG production vessel (that title goes to the Satu project of Malaysia's Petronas) it is easily the biggest.

The numbers behind Prelude, as they were for the Goose, are staggering. At 488m long and 74m wide the 600,000 tonnes LNG production vessel is the world's biggest ever floating object.

But, behind the gee-whiz engineering numbers there is another set of numbers which The Slug is yet to see - and he wonders why, with questions that spring to mind including:

•    What has Prelude cost to build?

•    What's the difference between the budget, as signed off on final investment decision day of May 11, 2011, and today?

•    When will Prelude achieve nameplate capacity of 3.6 million tonnes of LNG a year, plus 1.3 million tonnes of condensate and 400,000t of LPG?

•    What will a tonne of Prelude LNG cost to produce, and

•    When will Prelude be declared a financial success, as opposed to an engineering success?

That final point is a particularly interesting one because Shell will be quick to claim that Prelude is an engineering trial to prove the concept of large-scale FLNG production, not unlike Howard Hughes proving that his giant seaplane could fly.

If Shell does play the "engineering trial card" The Slug will be quick to remind its public relations apparatchiks that the original announcements about Prelude, and more recent comments by the company's CEO Ben van Beurden, emphasised the financial case for the project.

As Energy News reminded readers about this time last month, the Shell boss expects Prelude to generate "real material cash" in 2018.

Good luck to Ben, though it is worth pointing out that there is a difference between generating cash and producing a profit.

As far as The Slug can see Shell made a courageous decision in 2011 to proceed with its engineering marvel, though the decision would have been aided by an oil price at the time of around $US110 a barrel.

Oil today is half that price, but that's only the start in calculating the financial success of Prelude because missing from the equation is the cost of the barge, any construction delays and budget over-runs, and the time it will take to achiever nameplate capacity.

If nothing else, Prelude will be a fabulous project to watch in 2017 as it heads towards installation on site, hooking up to gas wells already drilled, gas liquefaction, first shipments and first cash.

Though a polite person might not ask about first profit, the capital payback time, and when Shell might be prepared to give the go-ahead for its second floating LNG production vessel.