Ace Tankers of the Netherlands has exercised an option for two stainless steel chemical tankers at Dae Sun Shipbuilding & Engineering.

The deal brings to six its tally of 33,000-dwt stainless steel tanker newbuildings on order at the South Korean shipyard.

Shipbuilding sources with knowledge of the order said Ace Tankers added the latest two by exercising an option it had held at the yard since April.

Ace Tankers is said to be paying about $47m each for the conventionally-fuelled ships, lifting its total spend on the vessel type to $282m.

The ships will be compliant with Phase 3 of the International Maritime Organisation's Energy Efficiency Design Index standards and Tier III NOx rules.

Dae Sun could not be contacted as South Korea is closed for a public holiday.

Ace Tankers is a joint venture between Eastern Pacific Shipping and XT Shipping.

The Dae Sun chemical tankers will be the largest the venture owns. The company controls some 40 tankers of less than 21,000 dwt. The ships are trading globally in a mixture of long-term contracts of affreightment and spot business.

Besides operating its own fleet, Ace Tankers is also acting as managing partner in the Ace Quantum Chemical Tankers pool.

The newbuildings will be the largest stainless steel tankers that Dae Sun has built. It is scheduled to deliver the sextet between the middle of 2023 and first half of 2024.

Several shipbuilding brokers said Dae Sun has temporarily stopped its ship sales marketing as it has already hit its $400m sales target for this year.

"Dae Sun's orderbook is booked until mid-2024," said a broker. "The yard plans to resume its marketing activities next year."

Clarksons' Shipping Intelligence Network lists the shipyard with an order backlog of 25 newbuildings. The orderbook includes 10 feeder containerships for SITC International Holdings, two MR tankers for Sea Pioneer Shipping of Greece and two 6,800-dwt chemical tankers from domestic owner Seong Ho Shipping.