Sinking Ship Effect

Causes
The sinking ship effect has been determined to be due to various causes:

Ocean Swells
It has been determined that at times the sinking ship effect is caused by bulges on the surface of the ocean.

See: Sinking Ship Effect Caused by Ocean Swells

Lack of Optical Resolution
The sinking ship effect can sometimes be caused by a lack of optical resolution whereby elements of the hull can seem to merge into the sea. This can be reversed with optical magnification.

See: Sinking Ship Effect Caused by Limits to Optical Resolution

Refraction
At other times the sinking ship cannot be reversed with optical magnification. In these cases the cause of the sinking effect is seen to be related to the common inferior mirage which regularly occurs for long periods of time over the surface of water. Over a period of time this sinking effect will disappear, revealing distant bodies.

See: Sinking Ship Effect Caused by Refraction

Inconsistency
It has been found that the Sinking Ship effect is inconsistent. At times it occurs and at other times it does not occur.

In The Plane Truth: The History of the Flat Earth Movement by Robert Schadewald we find:

From p.223 in Earth Not a Globe we read:

On p.217 we read additional accounts of inconsistency:

Time-lapse Photography
Indeed, modern time-lapse photography has verified that the sinking effect is inconsistent. See: Sinking Ship Effect Caused by Refraction