As the tide comes in, the dock and the boat rise with the tide. The rings rise up the pipes of the pipe dock.

The gangplank is hinged so it can swivel. Stairs would not make sense, because the angle would change as the tide changes.

No hinges or swivels on the bridge!

I took these yesterday in La Conner, Washington. This is the Rainbow Bridge over Swinomish Channel.

For the Ragtag Daily Prompt: swivel.