Q.What is the importance of Fresh water Allowance (FWA) and what is its relevance?

Freshwater density is  1.000

Seawater density is 1.025

water with density between fresh water and salt water = DOCK water

To maintain the reserve buoyancy vessels are only allowed to load up to the summer load line at sea water.

When the vessel moves from saltwater to fresh water due to the difference in density the vessel will sink so that summer loadline will submerge below water line.

This additional sinkage will be just enough to achive more underwater volume so that vessel will get exact buoyancy as the vessel floating in sea water.

This rise /change in draft is called as Fresh water allowance FWA.

RELEVANCE

FWA = W/(40TPC)

Summer draft + FWA = Freshwater draft.

If the vessel is loading in fresh water , She can load Upto fresh water draft.

When the Vessel travels from FW to SW, She will rise and her draft at salt water will be summer draft.