What is the reason behind that a ship sinks to a great depth in river water than in sea water?

Answer 1

equiring ships owners to put

load lines on ships and to use

them. Plimsoll's idea, known

as the Plimsoll Mark, is still

used all over the world.

Have you ever tried fl oating in the ocean?

In your bathtub? Which was easier? You

might have noticed it is easier to fl oat in

saltwater than freshwater.

It is easier for ships to fl oat in saltwater,

too. Two properties of water -- temperature

and salinity (saltiness) -- aff ect how deep a

ship's hull will fl oat below the water's surface.

Warm, salty water is easiest to fl oat in,

but not all ships stay in warm, salty water

as they move cargo around the world. How

do captains know their ships will stay afl oat

from one port to the next?

Imagine you are the captain of a gigantic

cargo ship. You loaded your ship in a

saltwater port in Japan, traveled across the

entire Pacifi c Ocean, and are heading to a

freshwater port in the San Francisco Bay to

unload.

As you travel from saltwater to freshwater,

your ship's hull will sink deeper into the

water. Your ship could be in danger if the

load is too heavy. It could run aground,

break a hole in the hull and, and, worst

of all, leak fuel and oil into the water. In

the 1860s, overloading was a big problem.

Some ship owners fi lled their ships with

more cargo than they could safely carry.

Over and over again these "coffi n ships"

sank. Many sailors died and the cargo sank

to the bottom of the sea. Some ship owners

did not care if they lost a ship or two.

Samuel Plimsoll (1824-1898) did care, and

was troubled by this thoughtless disrespect

for sailors' lives. He devised a simple line to

mark on the side of a ship to show the lowest

level it should sit in the water. Owners

could safely load a ship until it reached this

line, but no further.

The idea of load lines dates back to ancient

Greece and Rome, but there were no laws

in Plimsoll's time requiring them to be on

ships. Plimsoll fought for years to pass a

law, the Merchant Shipping Act of 1876,

Float

or Sink?

How do captains know how

to safely load their ships?

Photo: This is the Plimsoll

Mark on the port (left) side

of

Balclutha. The horizontal

lines show how deep a ship

can be loaded with cargo in

different waters. If the ship

was in fresh water (FW), she

could be loaded (sinking

down lower) until the water

was even with the line below

FW. If she was in salt water,

then she could be loaded to

the line below WNA (Winter

North Atlantic).

Answer 2

The salt content of sea water gives it greater density than fresh water, hence, objects floating in sea water will be more buoyant than they would be in fresh water.