Editing Ship (section)

== Measuring ships ==
One can [[Molded depth|measure ships]] in terms of [[length overall]], [[length between perpendiculars]], [[Waterline length|length of the ship at the waterline]], [[Beam (nautical)|beam (breadth)]], depth (distance between the crown of the weather deck and the top of the keelson), [[Draft (hull)|draft]] (distance between the highest waterline and the bottom of the ship) and [[tonnage]]. A number of different tonnage definitions exist and are used when describing merchant ships for the purpose of tolls, taxation, etc.

[[File:Brosen plimsoll line en.svg|thumb|load line mark (left) and load lines (right)]]
In Britain until [[Samuel Plimsoll]]'s [[Merchant Shipping Act#List|Merchant Shipping Act of 1876]], ship-owners could load their vessels until their decks were almost awash, resulting in a dangerously unstable condition. Anyone who signed on to such a ship for a voyage and, upon realizing the danger, chose to leave the ship, could end up in [[jail]]. Plimsoll, a [[Member of Parliament]], realised the problem and engaged some [[engineer]]s to derive a fairly simple [[formula]] to determine the position of a line on the side of any specific ship's hull which, when it reached the surface of the water during loading of cargo, meant the ship had reached its maximum safe loading level. To this day, that mark, called the "[[Plimsoll mark]]", "[[freeboard mark]]" or "[[load line mark]]",{{sfn|CLL|1966|pp=172–174|loc=Regulation 5}} exists on ships' sides, and consists of a [[circle]] with a horizontal line through the centre. On the [[Great Lakes of North America]] the circle is replaced with a diamond. Because different types of water (summer, fresh, tropical fresh, winter north Atlantic) have different densities, subsequent regulations required painting a group of lines forward of the Plimsoll mark to indicate the safe depth (or freeboard above the surface) to which a specific ship could load in water of various densities. Hence the "ladder" of lines seen forward of the Plimsoll mark to this day. These are called the "[[Load line (watercraft)|load lines]]"{{sfn|CLL|1966|pp=174–178|loc=Regulation 6}} in the [[marine industry]].