A project for a tranche of 12 midsize container ship newbuildings worth about $1.44bn has been floated to shipyards in China and South Korea, but its backers remain a mystery.

Shipping sources said shipyards are being asked for quotes on seven firm 7,000-teu vessels plus options for an additional five ships.

The company behind the newbuildings is not known but the enquiry is being circulated under the code name Project Knight.

Market talk about the identity of the end user for the newbuildings is rife. But several in the shipbuilding sector linked the vessels to Israeli liner operator Zim Integrated Shipping Services.

"Zim will be operating these 7,000-teu boxships and there is a chance that it may own the vessels directly. It may also charter them from a shipowner," said one shipbuilding source.

Zim did not respond to questions about the touted newbuilding project on Wednesday.

Should Zim be the end user, it will have a total of 27 boxships of 7,000 teu each, having chartered 15 LNG dual-fuel ships for 12 years that are under construction at Yangzijiang Shipbuilding from Seaspan Corp.

These vessels are slated to be delivered in 2023 and 2024.

Sources said the buyer is opting for LNG dual-fuel vessels and has specified the use of the high-pressure field gas systems. It has also requested that the vessels are to be installed with MAN ME-GI engines designed by MAN Energy Solutions.

They will also each be fitted with a 6,000-cbm type-C tank that will be located on deck.

Brokers estimate that dual-fuel container ship newbuildings will cost the mystery owner about $120m apiece.

A shipyard executive confirmed the Project Knight boxship newbuilding enquiry but declined to provide further information on the buyer or delivery dates for the vessels, saying his company had signed non-disclosure agreements.

A boxship source said container ships of 7,000 teu are popular with liner companies as they will be replacing the 4,250-teu vessels that were built more than 10 years ago. He said that besides Project Knight there are a few other shipowning companies enquiring about boxships of this size.

According to Clarksons' Shipping Intelligence Network, about 54 ships of 7,000 teu were ordered this year, of which 21 are LNG dual-fuelled and four are ammonia-ready.

Project Knight is probably the second code name container ship newbuilding enquiry to emerge in the shipbuilding market. The first was Project Slade, which appeared at the end of last year and involved 10 units of conventionally-fuelled 5,500-teu newbuildings.

France's CMA CGM was reported to be the mystery owner behind Project Slade. In April, it contracted China's state-owned Qingdao Beihai Shipbuilding Heavy Industry to build the 10 newbuildings to be delivered in 2023 and 2024.

CMA CGM was reported to be paying about $63m each for the panamax boxships. The design of the 40-metre beam vessels was carried out by Shanghai Merchant Ship Design & Research Institute. The panamaxes will be equipped with about 800 reefer plugs and will use WinGD's main engine.