Hydrometer Differences

Question 1

What is the difference between load line hydrometer and draught survey hydrometer?

Answer 1

Draft survey hydrometer is used to know the density of the sea water that will be used during draft survey for calculating the weight of cargo loaded. Loadline hydrometer is used to know the density of sea water that will be used for calculating the compliance with the loadline convention.

Question 2

What is the difference between Draft survey and Loadline hydrometer in terms of what they measure?

Answer 2

Draft survey measures the actual density of the water. Loadline hydrometer measures the Apparent density (also called specific gravity) of the water.

Question 3

What is specific gravity?

Answer 3

Specific gravity is the density in relation to something, which for water is in relation to fresh water at 15 C. It is a ratio, a number, and does not have any unit.

Question 4

When should you use a Loadline hydrometer?

Answer 4

You should use a loadline hydrometer if you want the dock water density to know how much you can submerge the load line and still comply with the load line convention. This gives you the specific gravity (apparent density) of the sea water.

Question 5

When should you use a Draft survey hydrometer?

Answer 5

You must use a draft survey hydrometer when calculating the weight of cargo loaded by draft survey, because you need to know the actual sea water density (and not specific gravity).

Question 6

How do you distinguish between a Loadline and a Draft survey hydrometer?

Answer 6

A loadline hydrometer measures specific gravity or Relative density, so it will have the marking of ‘RD’ or ‘Sp. Gr.’. Draft survey hydrometers have the unit of the density and temperature marked on them, for example ‘Kg/L at 15 C’.