jcjsnclsnc "jumbo shrimp" or "tiny whales"(or formerly living)!!

In general, size is what distinguishes the two, boats being smaller than ships, but the words' usage is more complicated than any one simple rule of absolute size can describe. The US Navy generally follows the "boats are smaller" rule, referring to its smaller vessels as boats and its larger ones as ships. (This notwithstanding that the designation USS stands for "United States Ship" and that some US Navy submarines are built, as least partly, by the General Dynamics Electric Boat Division-- the Newport News Shipbuilding division of Huntington Ingalls Industries Inc. also builds US Navy submarines, in whole or in part.) Also, the "three plus square-rigged masts" rule for sailing ships is, in practice, consistent with "boats are smaller" because small sailing vessels wouldn't benefit from three or more square-rigged masts-- other arrangements can work as well or better. Indeed, small sailing vessels would suffer from the weight and complexity of so many masts with so much rigging. Large sailing vessels, on the other hand, need the sail area such masts and rigging can provide in order to move, and the masts' and rigging's weight can be a much smaller proportion of a large vessel's total weight, while a large vessel can accommodate sufficient crew to handle the rigging's complexity. Vessels intended for navigation of coastal and inland waters are generally called boats, while ocean-going vessels are generally called ships. However, the former are also generally smaller than the latter. What it boils down to is the same issue one is confronted with when hearing of "jumbo shrimp" or "tiny whales". Provided that both terms refer to living (or formerly living) animals, one would hardly expect a jumbo shrimp to be larger than, or, for that matter, anything other than much smaller than a tiny whale. Use of words that attribute size-- small and large, big and little, jumbo and tiny, as well as many others-- is context-relative: one can confidently assume that a small watermelon is much larger than a large grape. The same is true of words that imply size, words such a boat and ship. The fact that perhaps not all boats are so small and not all ships so large that any ship could reasonably carry any boat is irrelevant. So is the fact that some boats are so large that trying to propel them only with oars might be no more effective than trying to propel a typical ship the same way. Categorically, boats are smaller than ships, in spite of the fact that the two categories overlap considerably. It's been suggested that the difference between a boat and a ship is that a boat's captain would not be offended to hear the boat referred to as a ship, while a ship's captain would be offended to hear the ship referred to as a boat. This may be true, but it's unlikely to be useful in determining which word to use in a given situation, since so few people have ready access to sufficient numbers of captains (of sufficient varieties of boats and ships) that they are willing to risk offending.