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.