Abstract
A maintenance policy for armour blocks is discussed to reduce total maintenance cost over an in-service period. The blocks are subject to waves which occur at a homogeneous Poisson process, suffer a non-negative random damage with an identical distribution. The random damage of armour layer is accumulated to the current damage level. If accumulated damage exceeds a threshold κ before catastrophe destruction, then the blocks are maintained preventively. An expected maintenance cost over the in-service period is derived. Numerical examples to minimize the expected maintenance cost are given. An expected value and variance of damage caused by a wave have great impact on an optimal preventive threshold $k$ to minimize the expected cost.
