E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Gang-board, or Gang-way (g hard).
The board or way made for the rowers to pass from stem to stern, and where the mast was laid when it was unshipped. Now it means the board with cleats or bars of wood by which passengers walk into or out of a ship or steamboat. A gang is an alley or avenue.
As we were putting off the boat they laid hold of the gangboard and unhooked it off the boats stern.Cook: Second Voyage, bk. iii. chap. iv.