Visibility is the maximum distance which can be seen on the horizon with naked eyes and without using any equipment. Good visibility is important for safe navigation and accident reduction. The officer on lookout will estimate the visibility all around the ship. Visibility on sea cannot be calculated, it should be estimated. It can deteriorate due to fog, mist, falling snow, heavy rainstorms, sandstorms or any other similar causes.

Causes for poor visibility:-

Dust haze/dust raising winds/dust storms: It occurs when the atmosphere is dry, large winds are created due to the steep pressure gradient. Because of these winds, in desert areas the dust will raised and will significantly reduce the visibility.This dust can move up to 3-5 kilometres. Visibility due to dust raising winds can be less than 1 kilometer.

Haze: Solid particles in the atmosphere like dust, sand, volcanic ash etc may travel from one place to another due to winds. This is called haze. The visibility may be higher than 1 kilometer, in rare cases it can reduce upto 200 meters. For haze to occur the relative humidity should be greater than 90%.

Spray:  When experiencing Beaufort scale wind force 9, spray reduces the visibility. When the waves from the sea hits the shore a spray of droplets of water is created. This droplets are carried by the wind. 

Fog: It is caused by the presence of very high quantity of water vapour. For fog the visibility will be less than 1 kilometer. It can occur if the relative humidity is 95 percent or more.
There are different types of fog:
 (i). Radiation fog: This type of fog occurs due to the over cooling of ground during the night. When the air comes below the dew point temperature, it condenses and the fog is formed. Favorable conditions for radiation fog to occur are highly saturated air, clear sky and light winds. 

(ii). Advection fog: It occurs when a moist airmass from any other place moves and comes in contact with a cold surface, the moisture condenses to fog and the advection fog is created. Fog we see on sea is an advection fog.

Mist: It is also caused as the same as fog, due to presence of high water vapour in air. But in case of mist, the visibility is higher than 1 km. 95% of the air must be saturated for it to occur.

Rain: At sea, rain can also reduce the visibility. The amount of reduction may depend upon the size of the rain droplets.