LONGER than an Olympic sized swimming pool and the largest vessel of its kind ever built, this is the first superyacht to be produced in Southampton by Palmer Johnson.

Known as a Sportyacht, the millionaires’ plaything is the first such luxury vessel built in the city since the £30m Mirabella V was launched by VT Group in 2003.

At 51m the yacht, currently known only as PJ-501, is a new size benchmark for Wisconsin based Palmer Johnson, but is just half the size of the yachts the company eventually hopes to build in Southampton. Mystery surrounds its affluent owner except that Palmer Johnson describes them as “a repeat client” and they have ordered another two of the Italian designed yachts. It’s destined to tour the Mediterranean later this year.

Although the firm has planning permission to create a purpose built facility in Woolston on the site of the former VT shipyard, it has yet to start work there.

Since 2008, Palmer Johnson has been operating on the former US Marine base in Hythe, which is now known as Hythe Marine Park.

The PJ-501 is the first in what is ultimately expected to be a production line of five or six massive yachts a year which at its peak could employ as many as 800 people.

Palmer Johnson president Mike Kelsey said: “This significant launch certainly cements Palmer Johnson's Sportyacht concept by passing the 50-metre benchmark and further confirms the appeal of the Sportyacht genre.”

The company revealed it also currently has orders for four further vessels, including two 64m sport yachts, each complete with two pools, one of which can be converted into a helipad and a giant 81m ice class vessel capable of sailing anywhere in the world’s vast oceans.