Ship

speed

Sailors

use

a

measure

called

a

knot

to

measure

distances

and

speed.

A

knot

equals

one

nautical

mile

an

hour.

If

a

ship

is

travelling

at

10

knots,

its

speed

is

18.52

kilometres

an

hour.

In

ancient

times,

sailors

used

a

knotmeter

to

determine

their

sailing

speed

in

knots.

A

knotmeter

was

a

rope

with

knots

tied

every

7.71

metres

along

the

rope.

A

sailor

threw

the

knotmeter

overboard,

and

the

speed

of

the

ship

was

determined

by

how

many

knots

went

out

during

a

certain

period

of

time.

Today,

a

ship’s

speed

is

measured

with

ultrasonic

instruments

that

use

sound

waves

to

measure

the

movement

of

the

boat.