Not much to add to all this but.... (in no particular order)

It isn't practical to tow a boat along a canal (or anywhere else) with a line attached at the front - like that the boat steers itself into the side and the steersman has to correct it all the time, which is inefficient. Tow lines are attached at or near the mid-point and the boat tows just fine, with minimal corrections necessary.

A "bowline on a bight" in fact makes a very good noose - you tie a small bowline, which gives you a small loop that won't close up under tension, and then run the bight of the rope through that to make a larger loop, which will - a slip-knot. Put that around your hangee's neck and string him up, you'll soon see!

True you can't undo a bowline knot while it is under tension, but it is one of those very useful knots that won't tension itself into an undoable mass if it is under strain. Once the strain is off, you can always get it undone again, which is why it is so widely used on boats.

Mooring a canal barge or a sailing ship which has long straight sides is different to mooring a curved side vessel like a yacht. A barge needs just two mooring lines, usually - a bow line and a stern line are sufficient to keep it in place. The curved sides of a yacht need to be held in place by a bow line and a stern line to stop it rotating around the widest point, and then a pair of springs (fore and aft lines) to stop it moving forward and aft under the influence of wind or current.

Singers of songs aren't always experts in nautical usage, so one is likely to hear different variations of pronunciation. And poetic licence comes into it somewhere as well!