Port-due on vessels not discharging or taking in cargo.

    When a vessel enters a port ²[not being a major port] subject to this Act, but does not discharge or take in any cargo or passengers therein (with the exception of such unshipment and reshipment as may be necessary for purposes of repair), she shall be charged with a port-due at a rate to be determined by the ¹[Government] and not exceeding half the rate with which she would otherwise be chargeable.