When a 700-foot Irving Oil tanker brings a cargo of petroleum products to the Sprague Energy Terminal on Mack Point in Searsport, or the Maine Maritime Academy training ship State of Maine sets sail with a cargo of merchant marine officers to be, the Penobscot Bay Tractor Tug Co.’s boats are generally on hand to assist. Last week, the 109-foot, 3,000-horsepower Fort Point pushed on the stern and the 3,500-horsepower Z-drive Fournier Tractor assisted with a line on the bow as the training ship got under way. PHOTOS BY STEPHEN RAPPAPORT