I think that the easiest and most effective way would be to add sound effects that would reflect escalation of the events. I.e., tense silience as the boat rides with its normal speed can change into nervos chatter, accompanied by the dying engine hiccups, then turn into indiscriminate shouts and screams, as the situation worsens. Soundscape is very important in your game as it is at establishing sense of place, and it can do more to enhance player's sense of presence at the scene.
On the visual side I would stay minimalistic, but maybe add some visual detail to indicate boat's state as it stops (maybe, smoke coming out of the boat?)