Big Boats: "Switzerland's Allseas plans world's largest construction vessel"

We noted the current record holder in May 2017's:

Shipping: Guy Says $3 Billion Boat "One Of The Bigger Bets Of His Career"

Which raises the question "What other bets have you made Mr. Heersma?"
Well, here's an upcoming speculation. From Reuters. Feb. 7:

Swiss offshore services firm Allseas is planning to build a vessel big enough to be able to remove the world’s largest oil and gas platforms when they reach the end of their production lives, its chief executive said.

The vessel, to be called Amazing Grace, is designed to remove the heaviest platforms in a single lift and could reduce decommissioning costs for global oil and gas producers, the firm said.

It would be a bigger version of Allseas’ existing Pioneering Spirit ship, which removed Shell’s Brent Delta platform in the North Sea last year, and would cost about $3 billion, Allseas CEO Edward Heerema told Reuters....MORE

These ships are basically two oil tankers strapped together:

  Lifting of the Delta topsides. Credit: Allseas

Pioneering Spirit measures 382 x 124 meters and is calculated at 403,342 gross tonnage. Note that gross tonnage is a calculation of enclosed volume times a multiplier and is not deadweight tonnage.

For that measure we go back to a different 2017 post, "Frontline Boss On Oil: "Fredriksen Expects Rise In Storage Of Oil On Tankers" (FRO)":

...Whenever you see the market with enough contango to make the cash-and-carry storage trade worthwhile I think of this sucker (now broken for scrap):



Capacity‎: ‎4,240,865 barrels o'crude.

From the Wikipedia page:

Seawise Giant, later Happy Giant, Jahre Viking, Knock Nevis, Oppama, and finally Mont, was a ULCC supertanker that was the longest ship ever built. It possessed the greatest deadweight tonnage ever recorded. Fully loaded, its displacement was 657,019 tonnes (646,642 long tons; 724,239 short tons), the heaviest ship of any kind, and with a laden draft of 24.6 m (81 ft), it was incapable of navigating the English Channel, the Suez Canal or the Panama Canal. Overall, it was generally considered the largest ship ever built. It was sunk during the Iran–Iraq War, but was later salvaged and restored to service. It was last used as a floating storage and offloading unit (FSO) moored off the coast of Qatar in the Persian Gulf at the Al Shaheen Oil Field....MORE

Here's how it stacked up against some other big boats (and buildings):...

And in a third measurement of size, January 2014's:
Natural Gas: Shell Launches The Largest Vessel Ever Built (displacement larger than six aircraft carriers) RDS
And we're not talking little French aircraft carriers either.
From Lloyd's:
Lloyd's covers largest ever floating vessel...

*****

... Giving the French their due, they are planning on building  Porte-Avions 2 - "aircraft carrier 2", using the plans for the future Queen Elizabeth class ships that perfidious Albion is cooking up.
 
And again giving the French a tip of the old chapeau they did build these monsters:

   Batillus class tanker, 555,000 DWT.