The correct answer is A) on a hawser tow. A fishplate is a metal plate used to connect the end of a towing hawser (line) to the towing vessel or the vessel being towed. This provides a sturdy and secure connection when towing another vessel using a hawser. The other answer choices are incorrect because fishplates are not typically used when towing alongside, running "light boat" (without cargo), or when pushing ahead or in the notch (a recessed area in the stern of the vessel being pushed). In those situations, other towing arrangements and connections would be more appropriate.