Final answer:
The Clove Hitch knot is typically used to tie fenders to a rail on a boat, thanks to its ease of use and adjustability.
Step-by-step explanation:
The knot commonly used to tie fenders to a rail on a boat is the Clove Hitch. It's known for its simplicity and ease of tying and untying. To secure a fender, make a turn around the rail, cross over the standing end and then make another turn and tuck the working end under the last turn before pulling it tight. It's essential to practice this knot to ensure it's tied properly, as a poorly tied Clove Hitch can slip under load.