Emergency services were called to Laxo on Wednesday night when the Whalsay ferry Linga had a small fire in one of her three engines while ten minutes into her scheduled crossing to Symbister.
The master of the Linga alerted Shetland Coastguard at around 10.15pm saying he was returning to Laxo after indications of a fire in the engine room.
On arrival at the ferry terminal crew members extinguished the fire with foam before local coastguard volunteers and the fire service arrived on scene.
The Linga will remain at Laxo while engineers from Shetland Islands Council investigate the cause of the fire. At present it looks as though the fire was started by a mechanical failure.
Council ferry manager Ken Duerden said the six passengers and five crew on board the Linga had never been in any danger.
The passengers managed to reach Whalsay on board the service's second ferry Hendra later the same night.
Duerden said: "This situation was handled quickly and efficiently by our onboard staff, but one of Linga's engines has sustained significant damage.
"Our engineers are assessing the situation, but in the meantime I'd ask passengers and service users for their patience while we run a restricted service into Whalsay."