One can measure ships in terms of overall length, length of the ship at the waterline, beam (breadth), depth (distance between the crown of the weather deck and the top of the keelson), draft (distance between the highest waterline and the bottom of the ship) and tonnage.
In Britain until Samuel Plimsoll's Merchant Shipping Act of 1876, ship-owners could load their vessels until their decks were almost awash, resulting in a dangerously unstable condition.