We have been advised by the Society of Master Mariners South Africa that a considerable number of cargoes of granite blocks weighing up to 40 tonnes each are presently being shipped from ports in Southern and Eastern Africa. We understand that there is an increasing tendency for such blocks to be stowed mainly in "drop-stow" i.e. in hatch squares, leaving large gaps between the sides of the stows of blocks (three or four high) and the ship's side frames (see photograph below).
A variation upon this is a "pyramid" stow, in which the bottom one or two blocks are floored out, ship's side to ship's side, and then a stepped stow made, ending up five or six high in the hatch square. In addition to being impossible to secure adequately, such a stow also has the effect of concentrating the weight of the stow in the centre of the hold, possibly exceeding the permissible "tonnes per square metre" tank top capacity in that area.
The reasons for such stowage may be due to the time taken to "wing out". Such stowage would also require the use of large capacity lift trucks, which are expensive for stevedores to purchase and operate and are frequently not available. It is far quicker and cheaper for shippers, charterers and stevedores simply to lower most, or all of these blocks into hatch square stowage.
By the very nature of this cargo, a ship loaded with granite blocks will have a large GM and be stiff. When subject to external forces such as beam swell, the ship will have a short period of roll and a tendency to jerk to the upright which may in turn place excessive strain on the lashings.