The pistons that spin the propellers are huge, but the visual impact is even stronger. Since Titanic is a period piece, the costumes, by Deborah Lynn Scott, had to be perfect. And they are. Nothing seems like it doesn't belong in the early 20th century. And then, there are the special effects.
Most special effects come across as effects, and nothing more.
Titanic uses special effects to enhance the realism of the story, not the other way around. The ship is brought to the screen via visual effects, models, and a near full-scale model. Watching people fall from the ship is incredible, and the death scenes were too realistic for some people in the audience. When the ship splits in half and lands back on the water, a gasp is heard from almost everyone in the audience. The music is terrific, and deserves the Oscar for Best Original Score.