meteorology- temps

Question 1

What are meteorological observations used for

Answer 1

forecasting, and planning operations such as cargo ventilation.

Question 2

To measure air temperature accurately the thermometer must be

Answer 2

shielded from direct radiation from the sun or other heat sources.

Question 3

The thermometer is placed in a Marine Screen, also known as a Stevenson Screen. This has a solid top and bottom, and louvred sides

Answer 3

to permit free flow of air while sheltering the thermometer from radiant heat, rain and spray.

Question 4

Why is the stevenson screen painted white

Answer 4

to reflect heat

Question 5

Why should the stevenson screen be hung on the windward side

Answer 5

To measure air temperature free of any influences from the ship

Question 6

How is humidity measured

Answer 6

Masons hyrdrometer

Question 7

What does a masons hydrometer consist of

Answer 7

This consists of a Marine Screen with two thermometers inside it.
One thermometer measures the air temperature. This is the Dry Bulb thermometer.
The other thermometer has a wick over the bulb leading to a reservoir of pure water.
The water migrates up the wick and keeps it damp.
Water evaporates from the wick drawing Latent Heat from it and reducing the temperature shown by the wet Bulb thermometer.

Question 8

The depression of the wet bulb is

Answer 8

the amount by which the Wet Bulb thermometer reads lower than the
Dry Bulb thermometer

Question 9

The rate of evaporation is

Answer 9

directly proportional to the temperature and inversely proportional to the
humidity of the air

Question 10

When temperature is high and / or humidity is low….

Answer 10

evaporation is rapid, drawing large amounts of latent
heat, and the depression of the wet bulb is large.

Question 11

When temperature is low and / or humidity is high…..

Answer 11

evaporation is slow, drawing small amounts of latent
heat, and the depression of the wet bulb is small.

Question 12

When the air is saturated

Answer 12

no evaporation occurs, no latent heat is drawn, and the depression of the wet bulb is zero.

Question 13

Why are temps read at 0.1°C

Answer 13

for humidity purposes

Question 14

In the MH how often must the wick be renewed

Answer 14

Weekly
And after rough weather when spray may contaminate the water

Question 15

In the MH how often must the reservoir be replenished

Answer 15

Weekly with pure water, or more frequently in conditions of low
humidity.

Question 16

Why is it important the the reservoir remains pure

Answer 16

Impure water evaporates at different rates, leading to inaccurate measurements.

Question 17

Precautions when observing temperatures:
The screen must be to windward
Why?

Answer 17

to minimise the effect of the ship.

Question 18

Precautions when observing temperatures:
Read the dry bulb then the wet bulb
Why?

Answer 18

as radiation is affecting them as soon as the door is
opened.

Question 19

Precautions when observing temperatures:
The dry bulb must be what?

Answer 19

Clean and dry

Question 20

Precautions when observing temperatures:
The wet bulb wick must be

Answer 20

Must be damp, not dripping, if temperature is above freezing.

Question 21

Precautions when observing temperatures:
The wet bulb wick must be what if temps are below freezing?

Answer 21

Must be coated with a thin layer of ice if temperature is below freezing. Water may have to be carefully applied, and the temperature allowed to stabilise.

Question 22

How is sea water temp measured

Answer 22

bucket method
hull sensor
engine intake

Question 23

What is the bucket method

Question 24

Ships making observations for the Meteorological Office are supplied with a specially constructed sea
temperature bucket.
This has a double skin and is constructed to

Answer 24

ensure flow through the bucket when it is towed through the
water.

Question 25

The bucket is attached to a line, which is attached to the ship.

• It is lowered into the sea clear of ___________ of water from machinery or cargo spaces.
• It is towed through the water to allow the bucket to acquire the ______ _____________.
• It is then hauled aboard and taken to a __________ location.
• The thermometer is inserted in the bucket and allowed to acquire the temperature of the water.
• The temperature is read to an accuracy of .° C without removing the bulb of the thermometer
  from the water.

Answer 25

discharges
water temperature
sheltered
0.1

Question 26

Hull sensor

Certain ships may be fitted with a _______ attached to the inside of the ship’s ____ just below the water
line which gives a remote measurement of sea temperature by conduction through the hull plating.

This is only suitable for ships whose ________ does not change significantly, or sensors may be fitted for light and loaded conditions.
The cabling required makes this an ___________ method.

Answer 26

sensor
hull
draught
expensive

Question 27

Engine intake

Other ships use the sea temperature measured at an intake of sea water to the engine room.
This is the least accurate method because:

Answer 27

• the point of intake is significantly below the surface
• the water entering the intake has been affected by the ship’s hull.