Ship & Naval

One can measure ships in terms of overall length, length of 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.
A number of different tonnage definitions exist and are used when
describing merchant ships for the purpose of tolls, taxation, etc.

In Britain until Samuel Plimsoll"s Merchant Shipping Act, 1876,
ship-owners could load their vessels until their decks were almost
awash, resulting in a dangerously unstable condition. Additionally,
anyone who signed onto such a ship for a voyage and, upon realizing the
danger, chose to leave the ship, could end up in jail.

Samuel Plimsoll, a Member of Parliament, realised the problem and engaged some engineers 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 Line", 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. This is called the "freeboard mark" or "load line mark"in the marine industry.