Metric Units

In the Ship Construction and Stability course you will be required to measure lengths, weights and volumes of cargo and vessels. It is therefore essential that you have a sound understanding of the units that are used to measure these quantities.

There are two systems of units used in North America: the Imperial system and the Metric system. This lesson will focus on the metric system of units of measurement. If you are interested in learning about the Imperial system supplementary materials are provided.

This lesson provides an introductory overview of the metric unit system. You will continue to use metric units in stability calculations as we move through subsequent modules of this course.

Metric units have three base units: metres, grams and litres. All other metric units consist of two parts: a prefix combined with a base unit. The prefixes are the same, regardless of which base unit you are working with. The following table shows the meaning of each prefix:

mega	M	1 000 000
kilo	k	1 000
hecto	h	100
deca	da	10
Base units: metre (m), gram (g), or litre ( L)
deci	d	0.1 or $\frac{1}{10}$
centi	c	0.01 or $\frac{1}{100}$
milli	m	0.001 or $\frac{1}{1000}$
micro	µ	0.000001 or $\frac{1}{1000000}$

Table 4.1

CLICK HERE TO PRINT THIS TABLE

Length:

The standard unit for measuring length in the metric system is the metre (m). To measure the dimensions of a barge you would use metres as the unit of measurement. For measuring the diameter of a rope you might use centimetre or millimetres depending on the thickness of the rope.
To measure travel distances, the nautical mile (nmi) is used, which is equal to the approximate arc length of one minute of latitude.

1 nmi = 1852 m

A commonly required calculation is the conversion of length from one unit, such as km, to another, such as nmi.

Example1: Convert 2 km into m

Solution:

Example 2: Convert 2cm into m

Solution:

Example 3: Convert 12nmi into km

Solution:

Mass:

The standard unit for measuring mass in metric system is the gram (g). In stability calculations, cargo weights can be expressed in kilograms (1kg = 1000g) or for larger loads, the metric tonne or just tonne(t) is used.

1 tonne(t) = 1000kg

Example 4: Convert 0.72t into g

Solution:

Example 5: Convert 12.45g into mg

Solution:

Example 6: Convert 8500000mg into t

Solution:

Capacity (Volume):

The capacity of any container is the amount of cargo it can hold, be that cargo solid, liquid or gas. This is the capacity or volume of the container. We will combine density and volume calculations in subsequent modules to determine cargo loads. The metric unit for measuring liquid volumes is the litre (L). The amount of liquid that a cube of side 1cm can hold is equal to 1milliltre (mL), that is, 1cc=1mL, where cc stands for cubic centimetre or cm3

Since 1 cm3 = 1 mL: A cube of side 1 metre (m) has a capacity of 1000 litres (L) or 1 kilolitre (kL). 1 litre (L) of water weighs 1 kg therefore: 1 cubic metre (m3) of water = 1000 L = 1000 kg = 1 metric tonne (t)

Example 7: Convert 1000 L into cubic metres (m³)

Solution:

Example 8: Convert: 14.67 daL into L

Solution:

Example 9: Convert: 25cL into dL

Solution: