Greenland ships, in the early ages of the fishery, were very indifferent structures, and even of late shipping of inferior quality were generally deemed sufficient for the trade. At present, however, when a good fishery is rarely made without frequent exposure to the ice, and sometimes in very critical situations, the vessels require to be substantially built, for the purpose of resisting the occasional pressure of, and frequent blows from, the ice, to which the ships of persevering fishermen must always be more or less exposed. The requisites peculiar to a Greenland ship, the intention of which is to afford additional strength, consist of doubling, and sometimes trebling, and fortifying. The terms “doubling” and “trebling,” are expressive of the number of layers of planks, which are applied to the exterior of a frame of timbers; hence, a ship which has one additional series of planks, is said to be doubled, and such ships as are furnished with two, or part of two, additional layers of planks, are said to be trebled. Doubling generally consists of the application of two or two half inches oak plank, near the bow, diminishing towards the stern to perhaps half that thickness, and extending in one direction from the lower part of the main-wales, to within six feet perpendicular of the keel forward, and to within eight or nine feet abaft; and, in the other direction, that is, fore and aft-wise, from the stem to the stern-post. Doubling is used for producing an increase of strength, and at the same time for preserving the outside or main planks of the ship from being injured by the friction of passing ice. Trebling, which commonly consists of one and a half to two inches oak plank, is generally confined to the bows of the ship, and rarely extends farther aft than the fore-chains or chesstree. It is seldom applied but to second-rate ships. Its principal use is to increase the strength of the ship about the bows, but it also, serves to preserve that part of the doubling which it covers from being destroyed by the ice.