pole used punt boat
篙 centers on a long pole used to propel or steer a boat by pushing against the riverbed or seabed.
篙 combines 竹 (bamboo) and 高 (tall), suggesting a tall bamboo pole. The character likely originated as a phono-semantic compound with 高 contributing the sound.
The top is bamboo 竹 and the bottom is tall 高. Picture a tall bamboo pole used to push a boat through shallow water.
For コウ, imagine a boatman calling out 'Go!' as he pushes the pole: 'Go!' -> コウ, and the tall bamboo pole moves the boat forward.