It is the duty of every outer-bar pilot to deliver to the master of any and every vessel approaching the Bay or Harbor of Mobile, as soon as he can board such vessel, all orders and letters which may be sent him for that purpose, on the person who requires the delivery of such letters paying or securing to the pilot $20.00 for such service, unless the pilot so employed to deliver such orders and letters is engaged as pilot for the vessel, in which event he is entitled to $5.00 for such service.