Singapore-listed offshore marine group Otto Marine has sold two 61-metre work maintenance vessels for US$30 million (S$38.3 million) in cash.

The buyer is Workboats 1, a wholly-owned subsidiary of Go Marine Services, Otto Marine said in a filing to the Singapore Exchange on Tuesday.

The vessels had been chartered to Go Marine Services, an associated company of Otto Marine, with a purchase obligation at the end of the charter period.

Otto Marine will recognise a net gain of about US$6.4 million from the sale of the vessels. It said the net proceeds from the transaction will be used to repay the group's bank loan, thus improving its working capital.