Hedge fund Raging Capital Management has lifted its stake in GulfMark Offshore to 19.9%.

The New Jersey investment firm reported to the US Securities & Exchange Commission that it owns 5.11 million shares in the Houston offshore vessel owner.

The stake is worth $28.1m at the most recent closing price for GulfMark’s shares on the New York Stock Exchange.

The William Martin-led firm has been steadily building its position in the company, where it emerged as a significant minority shareholder in May with a 12.9%