He could smash his way out through that door, and find something on deck to construct a raft from.

This was Lake Michigan, not the ocean, and not many hours would pass before he was picked up.

Vessels were constantly passing, and daylight would bring rescue.
But now the task became difficult.

He must find the girl, and serve her.
To his surprise, his heart beat rapidly in contemplation of the task.
Surely she must welcome his coming to her assistance now.

She would be alone, free to reveal the truth of all this strange mix-up of affairs; perhaps the old trust, the old confidence between them would be renewed.
At least in the midst of such peril, alone on the sinking yacht, facing possible death together, he would again discover the real Natalie Coolidge.