Some examples of grain cargo are – wheat, rye, maize, rice, oats, barley, pulses, seeds, etc
Hazards associated with grain cargo are
- Grain contamination and rottening
- Dust Explosion
- Depletion of oxygen
- Evolution of toxic vapour
Among the above hazards settling and shifting are among the most important.
Settling and Shifting
A compartment may be full when the cargo is loaded but, due to ship’s vibration and other movements, the grain settles by about 2 % of its volume leaving space at the top of the cargo. This space allows cargo to move from side to side in conjunction with the rolling and pitching of the vessel.
Grain has a low angle of repose (15 – 18 deg depending on the type of grain) and this results in its shifting very easily.
As the cargo shifts, the vessel lists to one side. The shifting of grain is the greatest hazard involved in the carriage of grain.
Thus the heeling moments for the ship are to be kept as small as possible
This is done by securing the grain surface to prevent shifting