Because originally she was a steam ship, but in the 50s she was converted to run on oil, which is what VSTEP have modeled, the Furie as she looked in the 50s
Ahoy there, landlubber NathanC
,
The Furie IS still a STEAM tug. The fact that she's not longer burning coal but oil does not mean that she's not a steamer. Just the means of heating the boilers changed from coal to oil want change that.
And even now in the 21rst century the Furie looks still the same as in the 50s of the 20st century. In fact, the means of burning didn't change here looks at all, except for the big, black smoke is no longer present.
Regards
Aad