Competence 1: Plan and conduct a passage KUP 9: Ability to use and interpret information obtained from shipborne meteorological instruments

KUP 9: Ability to use and interpret information obtained from shipborne meteorological instruments

sheng 2 Courses

Learning objective:

Aside from normal operation, the weather is one of the factors that makes the life of seafarers onboard the vessel more risky and dangerous. Luckily, different meteorological equipment is available today in aid for the seafarer in forecasting weather. Equipment like a thermometer, barometer hygrometer, wind vane, and anemometer are commonly available onboard the vessel and proved to be very important in predicting the weather.

Good weather forecasting will help the mariner make decisions for the safety of navigation and also reducing the risk in any other operation like cargo handling and vessel maintenance. However, a sailor should remember that he must have the appropriate knowledge on how to use the equipment, and read and interpret various information the equipment provides. Inaccurate reading and interpretation of different meteorological equipment may be very dangerous for the vessel and its crew.

The learning objectivie is to develop the ability to use and interpret information obtained from shipborne meteorological instruments

Learning content:

1. Wind Vane/Amemometer

A wind vane is an instrument that measures wind direction while anemometer measures wind speed. The illustration shown in the left side is a combination of wind vane and anemometer. This type of instrument are commonly installed on the ship.

To determine wind direction, a wind vane spins and points in the direction from which the wind is coming and generally has two parts, or ends: one that is usually shaped like an arrow and turns into the wind and one end that is wider so that it catches the breeze¹.

The measuring principle of anemometer is simple: the stronger the wind blows, the faster the half-open plastic cups turn. The speed of the cross rotation determines the wind speed. The cup anemometer records the number of rotations per minute and thus the wind speed very accurately.

Information obtain by wind vane and anemometer are converted and can be read directly form ship’s bridge.

2. Psychrometer

The common instrument used to obtain dew point and relative humidity is a psychrometer, which consists of two liquid-in-glass thermometers mounted side by side and attached to a piece of metal that has either a handle or chain at one end. The thermometers are exactly alike except that one has a piece of cloth (wick) covering the bulb. The wick-covered thermometer—called the wet bulb—is dipped in clean water, whereas the other thermometer is kept dry².

3. Thermometer

Thermometer is an instrument used to measure temperature.

In a vessel, it is important to have an instrument that can measure the temperature of sea surface. Commonly used thermometer on the ship is the “bucket instrument” method which is the simplest and most probably the most effective method of sampling. Due to the advancement of the technology newly-built vessels today has hull-attached thermometers that provides input digitally.

4. Aneroid Barometer

The most common type of barometer—the aneroid barometer—contains no fluid. Inside this instrument is a small, flexible metal box called an aneroid cell. Before the cell is tightly sealed, air is partially removed, so that small changes in external air pressure cause the cell to expand or contract. The size of the cell is calibrated to represent different pressures, and any change in its size is amplified by levers and transmitted to an indicating arm, which points to the current atmospheric pressure.

Barometer has 2 pointer, the black and the gold. The black indicator hand always points to the current air pressure while the gold indicator hand can be used as guide from your last reading to easily observed changes of pressure and can be adjusted manually. Change to high pressure means good weather is ahead while a change to low pressure means bad weather is on the way².