9. WEIGHTS AND MEASURES

The dimensions and weights used in this booklet are all given in metric measurements.

LINEAR MEASUREMENTS

This is how to convert inches, feet and yards into metres:

VOLUMES

The basic metric unit for volume is the cubic metre which is made up of 1 000 litres. The cubic metre is abbreviated in the form m³.

This is how to convert gallons into litres and cubic metres:

AREAS

Areas of land are usually measured in local units, which differ from country to country.

In engineering, however, the metric unit of measurement is the square metre (m²). Large areas are measured in hectares (ha) and vast expanses in square kilometres (km²).

1 hectare = 10 000 square metres
1 square kilometre = 100 hectares

This is how to convert square feet, square yards and acres into square metres:

WEIGHTS

This is how to convert ounces and pounds into grams, kilograms and tonnes:

Some useful weights
It is useful to know that:

• 1 litre of fresh water weighs 1 kg;
• 1 m³ of fresh water weighs 1 000 kg;
• 1 m³ of sea water weighs 1 020 kg; The volume of fresh water 1 000 mm x 1 000 mm x 1 mm (i.e. 0.001 m³) is equivalent to 1 litre and accordingly weighs 1 kg;
• 1 m³ of cement powder weighs approximately 1 800 kg;
• 1 m³ of limestone aggregate weighs roughly 2 100 kg.

Aggregate made from crushed coral weighs much less depending on the porosity of the coral.

Concrete. 1 m³ of concrete made with normal aggregates weighs about 2 300 kg. Concrete made with coral aggregate may weigh as little as 1 500 kg per m³.

However, 1 m³ of normal concrete immersed in sea water has an effective weight of less than 2 300 kg. This is caused by the uplift of the salt-water and should be borne in mind when casting anchor blocks for vessels. For example, the submerged weight of a concrete anchor block measuring 400 mm x 400 mm x 300 mm can be calculated as follows:

Volume of anchor = 0.4 x 0.4 x 0.3 = 0.048 m³
Weight in air = 0.048 x 2 300 = 110 kg
Uplift in water = 0.048 x 1 020 = 49 kg
Submerged weight = 110 - 49 = 61 kg

Hence, although the 110-kg anchor block is heavy to handle, it only provides 61 kg of pull when placed in water and may drag along the bottom during rough weather.

Timber. The weight of timber varies according to the species of tree. Here are some examples:

• Opepe weighs about 750 kg/m³;
• Teak weighs about 640 kg/m³;
• Ironbark weighs about 1 120 kg/m³;
• Greenheart weighs about 1 040 kg/m³;
• Red louro weighs about 640 kg/m³;
• Blue gum weighs about 830 kg/m³.

As these weights show, both greenheart and ironbark weigh more than sea water and, so, do not float.

Metals. The weight of a sheet of the following metals, 1 m² x 1 mm thick (that is a volume of 0.001 m³), can be expressed as follows:

Aluminium	weighs	2.56 kg
Zinc	weighs	7.20 kg
Steel	weighs	7.80 kg
Brass	weighs	8.55 kg
Copper	weighs	8.90 kg
Lead	weighs	11.37 kg

CONVENTIONS

Civil engineering, like other branches of engineering, follows preset rules of presentation in order that drawings and plans can be easily read and understood.

Dimensions. On normal drawings, dimensions up to 10 m are usually expressed in millimetres. Over 10 m, dimensions may be expressed directly in metres. Diameters are usually expressed in millimetres; a 100-mm diameter pile is expressed as "Ø100".

Levels. Levels above and below mean sea level are usually expressed in metres up to two decimal places. A quay 1.5 m above sea level is said to be at +1.50 m. Similarly, a sounding that is 2 m deep is expressed as -2.00 m. When there are tides, which change the depth of the water, all levels should refer to chart datum or low water spring level (LWS) (see Figure 22).

Symbols. The symbols for sand, rock, etc., used in this booklet are internationally recognized symbols (Figure 105).

DRAWING SCALES

All drawings, apart from sketches, are drawn to a scale (Figure 106).
Drawing scales are necessary to represent actual construction dimensions on paper.
A scale of 1 to 50 or 1:50, means that a length that is 20 mm on the drawing represents 50 time 20 mm, that is 1 m, in real life.
Moving to a smaller scale of 1:100 (the scale 1:50 is twice as big as the scale 1:100), a length of only 10 mm represents 1 m.

Similarly, on an even smaller scale of 1:200, 5 mm represents 1 m.

What scale and size of paper should be used? The international printing paper A-series is a very common standard and should be used:

A1-size is 841 mm long and 594 mm wide.
A3-size is 420 mm long and 297 mm wide.

Layout drawings of shelters or harbours should be as big as possible. For example, a stretch of coast 168.2 m long will just fit on to an A1-size paper (841 mm long) if it is drawn at a scale of 1:200 (200 x 841 mm = 168.2 m). If a scale twice as big, 1:100, is used only half the above length, or about 84 metres, would fit on to the same piece of paper.
Construction details, such as cross-sections, require a scale no bigger than 1:50, preferably 1:20.