With 15 crew members on board, including a 15-year-old boy and his father, the vessel was carrying out operations in the Rosebank oil field when the emergency occurred.
THURSDAY 12 APRIL 1710 BST
A Mayday call is issued by the acting officer on the Transocean Rather drilling unit after the Bourbon Dolphin overturns while carrying out anchor handling operations.
Two rig supply vessels working near the scene of the stricken boat begin an immediate rescue bid for crew members and pull seven from the sea.
THURSDAY 12 APRIL 1820 BST
Shetland Coastguard helicopter arrives at the scene and removes two more crew members from the water.
THURSDAY 12 APRIL 2200 BST
Two helicopters arrive in Shetland carrying seven surviving crew members.
The search and rescue operation for the five remaining crew members continues as light fades.
THURSDAY 12 APRIL 2300 BST
A down-manning of the Transocean Rather rig begins to remove all 70 non-essential personnel from the platform after it is discovered the overturned tug is still attached to the rig via the anchor line.
The intensive search and rescue operation being carried out by RAF and Bond helicopters to find the missing crew members is scaled back due fading visibility. A Nimrod is also in the area helping with the search.
FRIDAY 13 APRIL
At first light the search to find the five crew members, including a 15-year-old boy, resumes.
RAF divers arrive at the scene to begin investigations of the capsized tug to determine whether it is safe to enter the vessel.
An ROV (remote operating vehicle) carrying a camera is sent to investigate the stricken Bourbon Dolphin. Hopes of finding the five crew members alive are fading.
FRIDAY 13 APRIL 1345 BST
Divers are still on scene searching using the ROV but have not found anything up to this point.
The weather at the scene is worsening which has made it too dangerous to dive themselves. If the weather does not get better they will return to Faslane on the Clyde.
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