Abstract
In order to estimate the main hopper side slope in the cargo holds of self-unloading ships, a triangular, rigid, powder block was assumed at the transition of the walls of the cargo hold. When a given size of the powder block just slid off the hopper walls, the critical hopper slope was calculated from the force balance on the powder block.
The calculated critical hopper slope increased with a decrease in the size of the powder block, and a maximum value was obtained when the powder block became infinitely small. For the desigh of the cargo hold, this maximum value was taken as a lower bound of the main hopper side slope.
When assuming that the cargo hold is for carrying coal, the calculated hopper slope was 40°against an ulrta high molecular weight polyethylene plate, and was 51°against a steel plate. These calculated results were slightly large in comparison with the main hopper side slope adopted in the cargo holds of existing self-unloading ships. Consequenty, a low hopper slope required both a low frictional coefficient and a low adhesive force between the powder and the wall material of the hopper.
