An angle of loll situation can arise in a ship for a number of reasons:
- Ships carrying timber deck cargoes
(Deck cargoes will absorb moisture that will cause G to rise. An allowance of 15% of the weight of timber carried on deck should be made when conducting calculations and determining GZ values for the condition in question.)
- Consumption of fuel and water and introduction of free surfaces
(Fuel and water will be consumed from low down in the ship raising G due to the removal of weight from low down in the ship and the introduction of free surfaces in tanks that may have been initially full. Even ballast tanks that are initially full may become slack as a voyage progresses due to the constant rolling and pitching of the ship at sea causing water to escape from tank air pipes on deck. Tanks may require to be topped up occasionally, particularly when stability is considered marginal at any stage during the voyage. Poor cargo and ballast tank management resulting in excessive free surface moments is the most common cause of loll situations excepting damage scenarios.)
- Heavy lift operations using ship’s lifting gear
An instantaneous loss of GM will take place immediately that a weight is lifted either off the deck or from a position over the side. Such large increases in KG must be considered prior to any heavy lift operations and calculations should be conducted prior to any such operation to ensure that:
- The ship has adequate stability at all stages during the lift, and;
- Maximum list is restricted to an acceptable limit.
- Shift of bulk cargo
The vertical component of a shift of solid bulk cargo may be sufficient to reduce GM sufficiently to cause a loll situation, particularly if accompanied by one of the above. The larger horizontal component will also create listing moments compounding the situation further.