A boat displaces it's own weight of water, when floating.

The trick is to make sure that there is enough waterplane area and freeboard, to stop water coming in and making it heavy enough to sink.

The ship is box that is never symmetrical about its central axis as built

Also due to various drafts tythe waterplane in real differs from theoretical waterplane

Hence the 6 points drafts ,read at stem, midship and aft ,are first corrected to Length between perpendicuar , then list and trim , brionging the mean hydrostatic draft very close to tabular draft of designed ship

mere mean drafts could indicate higher submergence due to sag ( loaded heavy in middle ) or hog( loaded heavier in end holds)

Simple measurement is the only way to get displacement.

shortest distance between source and destination which is nothing but a straight line joining the two :)

The displacement of a vessel is the weight of a vessel. It will displace its own weight of the fluid in which it is floating.

There is no common equation for this, as it will be governed by the hull shape.

On commercial vessels, the calculations need support from tables, which tabulate different waterplane areas with the draught.

"Area" in Afrikaans is "area."