The 3,970 dwt Tugberk Imamoglu collided with the 3,338 dwt chemical tanker Alsu around 18 nautical miles south of Silivri, west of Istanbul, shortly after 03.00 local time. Turkey’s maritime authorities say an emergency signal from Tugberk Imamoglu’s EPIRB was received at 03.26. The master of Alsu subsequently contacted vessel traffic services at 03.41 to report that his vessel had collided with an unidentified ship around 03.15.     Repeated radio and telephone attempts to contact Tugberk Imamoglu and its 10 crewmembers have failed. Authorities now believe the vessel has sunk.     Fourteen maritime search and rescue units, a helicopter and Alsu are involved in the operation. Survival equipment belonging to the missing vessel, including its free-fall lifeboat, has been located on the water, but no crewmembers had been found at the time of writing.      The 1990-built Tugberk Imamoglu, owned by Istanbul-based Zeybe Denizcilik, was sailing from Iskenderun towards Karadeniz Eregli.    The 2021-built Alsu, owned by Ozpulathane Deniz Tasimaciligi, was travelling from Kocaeli to Aliaga. Initial inspections found no visible damage to the tanker.