i-catch-cartags,
Guys down here use heavy metal electrical conduit formed with a large bend (Sheppards Hook) on one end to reach around the pilings of the oil & gas production platforms. Drill a hole in the opposite end and put on a clevis and tie your rope to it. Let out any length you want and tie off to the boat.
You can form these to ahere to the shape of your bridge beams or pilings.
And they are economical.
1perchjerker