Fire crews were called to the scene in Peterhead Harbour at around 3am and had the blaze under control within two hours.
At the height of the incident 35 firefighters were involved in tackling the fire on the Fugro Symphony, an offshore supply vessel.
The 84 crew on board were evacuated to the Fishermen’s Mission in Peterhead, the Scottish Fire and Rescue Service (SFRS) said.
There were no reports of any injuries.
The SFRS had five appliances, a foam unit and an incident support unit at the scene.
It is not known how the fire started.