The pirates attacked the Bremen-based Beluga Nomination around 800 sea miles north of the Seychelles, prompting reaction from a Seychelles patrol boat and a Danish warship in the area.
The Seychelles patrol boat fired on the ship killing two pirates and two crew members, reported Der Spiegel on Saturday. Yet it was unable to gain control of the Beluga Nomination, and most of the surviving crew locked themselves into a safe room.
At least two others jumped into the free-fall life boat and activated it, plunging into the sea.
The day afterwards the Beluga Nomination stopped as the daily fuel ration was seemingly exhausted. A few hours later another captured ship, the York gas ship arrived, and the two ships were last seen heading towards Somalia.
The two men in the life boat were picked up by the Danish frigate and are said to be in as good a condition as could be expected under the circumstances. A Beluga shipping company spokeswoman confirmed that the fate of the rest of the crew remained unknown.
On Friday Somali pirates attacked another German ship, the New York Star tanker which belongs to the Hamburg firm Chemikalien Seetransport.
It was attacked by pirates in a speedboat, a firm spokesman said on Saturday. The captain tried avoidance manoeuvres while the crew locked themselves in a safe room. The Dutch frigate De Ruyter came to its aid and soldiers boarded to check for pirates before giving the all-clear.
New York Star will continue its journey from Saudi Arabia to Singapore with its load of naphtha.