At the International Congress in Paris, in 1802, about the equalisation of the measuring system, it was decided that the unity of length would be the metre, shortened to m. For the unity of weight, the kilogram was introduced.
The purpose of this decision was to take away the arbitrary character of measures and weights by relating the metre in a certain proportion to a natural magnitude. The definition of the metre was revised a couple of times, because more accurate ways of measuring were introduced, which revealed there imperfection. So other definitions, with smaller error margin, had to be found.
The definitions of the metre:

~In 1802 the metre was 1/ 10.000.000 part of the meridian over Paris from the North Pole to the equator. A standard metre was manufactured in platinum, which was kept in Paris.
~In 1879 the metre was said to be the distance between two scratches on a (new) bar of platinum-iridium, at 0°C. This new metre was not accepted internationally until 1889.
~In 1960 the metre was again re-defined. This time as 1,650,763.73 times the wavelength of the orange-red line of krypton-86, propagating in vacuum, at 0°C and 76 cm Hg-pressure (Airpressure at sea-level).
~In 1984 till now, the metre is defined as the length of the path travelled by light in vacuum in the time interval of 1/ 299,792,458 of a second.

The unity of weight is the kilogram (kg).
A kilogram (10³ gram) is the weight of 1 dm³ of fresh water at a temperature of 0°C.

B efore the metric system was introduced, in all countries weighting and measuring was done with historical grown units. Those were adopted from every day's objects or limbs: stone, foot, el (yard), duim (inch) etc.
In the Middle Ages ages about every town had its own measuring system. The Netherlands took over the metric system in 1816. But the Amsterdam 'voet' was still used in 1900.
Great Britain, the Common Wealth and the United States kept the old system, which was therefore named the Imperial System. Around 1980 the U.K., at last, took over the metric system. The Imperial System is also standardised. For example:
1 Fathom = 2 yards = 6 feet
1 Foot = 12 inch
1 Nautical Mile = 10 cable
1 Imperial gallon = 4 quarts
1 Quart = 2 pints
1 Pint = 4 gills
etc.
There are a few substantives used in navigation, which express a certain length.
The coil is a roll of rope and it usually has a standard length of 120 fathoms. When three ropes of this length are laid together, a cable of 100 fathoms length is created. That is a cable length and is considered to be 1/10 of a nautical mile.
Anchor chain is forged in pieces of 15 fathoms. Those lengths of chain are put together with D-shackles to a desired total length. When anchoring, the length of chain ran out the hawse hole is counted in the number of marked shackles that has passed. So if a ship is behind '5 shackles' at anchor, she lies behind a length of chain of 45 fathoms .

The monetary unit in the United Kingdom is the pound sterling. The pound sterling had an almost untouchable position in the world till after World War II. One pound used to be equivalent to 20 shilling, a shilling used to be 12 pence. From 1971 the pound sterling was converted to the metric system: the new pound was divided into 10 shilling of 10 pence each.
Below there is a list of exchange rates of 1896. Of course, currency is always subject to fluctuation, but this list gives an idea of the values of different currency in the 19th century so one can compare the freights and the costs of shipbuilding, exploitation etc. when mentioned. All figures are related to the mighty pound sterling.

	1896		2000
One pound	4.8	U.S. Dollar	1.58	U.S. Dollar
	12	Dutch Guilder	3.6	Dutch Guilder
	48.5	Danish Krone	12.2	Danish Krone
	7.8	Norwegian Krone	13.3	Norwegian Krone
	7.8	Swedisch Krona	13.8	Swedisch Krona
	20	German Mark	3.2	German Mark
	24	French Franc	10.7	French Franc
	10.6	Eng.-Indian Rupee	68.7	Indian Rupee
	24	Italian Lira	3167.4	Italian Lira

The Euro values 1.64 (March 2000).

The statute mile or land mile is derived from the Roman road distance milia. A milia is equivalent to 1000 passus, a passus is 1.48 m. The English land mile however is declared to be 1609.30 m.

The nautical mile or International Sea Mile (M) is the length of arc of one great circle minute. In 1929 the nautical mile is recalculated and established at 1851.85 m. In daily use the mile is rounded to 1852 m. 
A knot is a nautical mile per hour.

The Geographical Mile or German mile is a fifteenth part of a degree of arc of a great circle. A degree of arc equals 60 minutes of arc, so 1 German mile equals 4 nautical miles. In the 19th century the Germans and Dutch used this German mile in their navigation to express distances at sea. I can imagine that more countries used this mile, like the Scandinavians, but I don't know for sure.

The terms Gross- & Net Tonnage do not refer to tons of weight, but they refer to a volume measurement within a ship, expressed in Register Tons. This term found its origin in the early Dark Ages in the wine trade between France and England. The French word for a big-bulged barrel is tonne. So the number of tonnes a ship could carry was an easy reference for capacity.

Today the Gross Tonnage is, broadly speaking, the capacity in cubic feet of the spaces within the hull, and of the enclosed spaces above the deck available for cargo, stores, fuel, master, crew and passengers, with a couple of exceptions, divided by 100. Thus 100 cubic feet of capacity is equivalent to 1 gross ton (= 2.83 m³).

The Net Tonnage is the gross tonnage diminished with the spaces used for the accommodation of the master, crew, navigation and propelling machinery.
I do not know how the gross - and net tonnages were defined in the days of sails.

The Measure Ton in general is a ton of 40 ft³, which is used in freight calculations.
Another measure ton is the shipping-ton of 50 ft³. See stowage factor.

There are three kinds of tons:
The metric ton of 1000 kg.
The long ton of 1016 kg (=2240 lbs = 160 legal stone = 1 English ton).
The short ton of 908 kg (=2000 lbs).
The metric- and long tons are both used in navigation. The short ton is used in the U.S. and Canada.
In the middle ages there was another weight in use. This was the load or rye-load (roggelast). A rye-load is 1976.4 kg, so that is almost 2 tons. Besides the volume capacity it is (....)

Besides the gross - or net tonnage, often mentioned in literature, there are the magnitudes displacement, deadweight and cargo capacities.
The displacement is the weight of the volume of water, which is displaced by the ship. The displacement is the total weight of the ship and everything onboard at a certain moment. The draft of the ship depends on the specific gravity of the water where it is in. In seawater, with a s.g. of 1.025 ton/m³, the ship will sink in less then in fresh water, which has a s.g. of 1 ton/m³.

The volume of the hull that is submerged can be calculated. The results of those calculations on various draughts are put together in the carene diagram. This diagram is used to determine the displacement at a given draught fore and aft. It might be necessary to take the specific gravity of the water with a salinometer. The weight of the 'empty ship' is the weight of the ship with only the permanent inventory on board, no ballast, no bunkers nor stores.
Deadweight is the weight in tonnes (1000 kg) of cargo, stores, bunkers, fresh water, ballast, passengers and crew carried by the ship when loaded to her maximum summer loadline. Or in other words: Deadweight is the displacement of the ship, loaded to her maximum summer loadline, substracted with the weight of the 'empty ship'.
If one diminish deadweight with stores, bunkers, fresh water etceteras, the cargo capacity remains. This is the actual amount of cargo a ship can carry in that condition.
The difference of deadweight and cargo capacity on a sailing ship is only a couple of tonnes, I guess. But for a mechanical powered ship the differences are significant, due to the bunker capacity.

A ship can be fully loaded in three ways:

1. It can be full in weight when it is at its maximum draft
2. It can be full in space when the hold is filled up to the hatch covers
3. It is full in weight as well as in space (full and down)

In what way the ship will become full, depends on the kind of cargo it loads. For convenience' sake we only look at homogeneous cargoes.
The space taken in by a certain product for a ton of weight is called the stowage factor and it is expressed in ft³/ton. The earlier mentioned 40 ft³/ton is about average a lot of products.

If a ship is fully loaded with bales of wool, with a stowage factor of 165 ft³/ton, the ship's hold is full long before it is at its maximum draft. On sailing ships they had to take ballast in before loading the wool, to reach a minimum draft needed for stability.
On the other hand, if a ship is loaded with nitrate in bulk, which stows 30 ft³/ton, the ship will sink in to its scuppers before the hold is half filled. In the days before the restrictions for maximum draft were settled, it was for the captain to decide when the ship was full and still seaworthy.
The stowage factor of the cargo that brings the ship 'full and down' is also called the loading factor.

Length extreme (L_ex) is the extreme length of the ship, that includes  jibbooms, davits at the stern and on today's ships bulbous bows etc. For sailing ships it is also called the 'sparred length'. If you take away the removable parts, like the jibboom, you have the 'Lenght overall'.
'Lengte over alles' in Dutch.

Length between perpendiculars (L_bp) is the distance on the summer load waterline from the fore side of the stem to the after side of the rudderpost, or to the centre of the rudderstock, if there is no rudderpost.
'Lengte tussen de loodlijnen' in Dutch.

Length between stem and stern (Lbss) is the length between the insides of the rabbets of the stern- and stempost, measured on the maindeck.
'Lengte over de stevens' in Dutch.

Sheer is the fore and aft camber of the deckline, from midships up to stem and stern. It is not to be confused with sagging were the structure of the ship is affected by wrong loading or infirmity of old age of the ship. Hogging is the opposite of sagging and a more common phenomenon, because the mid section of the ship has the greatest buoyancy.
'Zeeg' in Dutch.

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Extreme breadth is the breadth on the outside of the ship's structure. Including the wales etc.
'Breedte buitenwerks' in Dutch.

Breadth moulded is the breadth amidships from the heel of frame to the heel of frame. The difference between the breadth extr. and moulded is at least the thickness of the hull plating or planking.
'Breedte volgens de mal' in Dutch.

Draft or draught is the vertical distance between the waterline and the underside of the keel.
'Diepgang' in Dutch

Depth is the vertical distance in the hold between the underside of the deck beam to the top of the keelsom.
'Holte' in Dutch.

Camber is the vault of the deck atwarth-ships, which is in fact the vault of the beam supportinfg the deck. This vault or curve gives the deck more strenght, a better drainage and on the man of war it reduced the recoil of a cannon etc.
'Balktrek' in Dutch.

Thumblehome or housing in, is the vaulting of the shipssite from the waterline to the rail. 
'Invalling' in Dutch.

Fahrenheit
G abriel Daniel Fahrenheit (1686 - 1736) was a German-Dutch physicist. He lived in Amsterdam when he manufactured the first mercurial thermometer in 1715.
As a zero he marked his mercurial thermometer when it was placed in the freezing mixture of sal-ammoniac salt and ice. According to Fahrenheit this was the lowest temperature possible on earth. Then he took the human body temperature and declared that to be (8 x 12) 96°. Extrapolating this number to boiling water at sea level. He took two fixed points to marke his scale: melting ice in water at 32° and boiling water at sea level at 212°, which is a range of 180° F.

Celsius
Anders Celsius (1701 - 1744) was a Swedish astronomer and the inventor of the thermometer scale that bares his name.
Celsius took a thermometer and stuck it in water with melting ice. He marked his scale at this point. Then he put the thermometer in boiling water at sea level and marked the scale again. The range between the two points was equally divided into 100 degrees. Celsius called the melting ice 100° and boiling water 0°. In later days that is turned around, so melting ice equals 0°C and boiling water is 100°C. 

It is important to boil the water at sea level. Sea level is about the lowest point where mankind lives. (except for some fools who live behind dykes below sea level) If you boil water up on a mountain, it will start boiling at 90° or so, because of the lower air pressure.

Converting Celsius to Fahrenheit goes as follows:
°F = (°C * 9/5) + 32   or   °C = (°F-32) * 5/9

Kelvin
Lord William Thomson Kelvin of Largs (1824 - 1907) was an English physicist. He graduated at Cambridge at the age of 21.
He developed his scale of temperature in 1848. The units of scale are equal as those of Celsius, but his zero is the absolute zero of temperature. It is the temperature where the movement of molecules has stopped. This means that 0 K = -273°C, or 0°C = 273 K. ( 273,15 K to be exact).

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