The coastguard helicopter was scrambled early on Thursday morning after a fishing vessel with five crew started taking on water 37 miles north of Unst.
Coastguard teams received the call at 5am regarding the Tranquility with a mayday relay going out shortly afterwards and other nearby fishing vessels assisting.
After getting to the scene, a winchman lowered a salvage pump on to the vessel at 6am to get the situation under control.
The Aith lifeboat was also launched and arrived at around 8am with the other vessels that had been assisting going back to fishing.
The Lerwick lifeboat is expected to meet the Aith lifeboat, which has been escorting the Tranquility south, off Fetlar with the Lerwick vessel escorting the fishing boat the rest of the way to Lerwick Harbour.