A fleet bought in one year ends in the same period, but the average age does not show it. Two fleets of twenty containers can both average five years: in one all twenty are five years old, in the other ten are new and ten are ten years old.
| Fleet | Distribution | Average age |
|---|---|---|
| A | 20 containers, all 5 years old | 5 |
| B | 10 containers 0 years old, 10 containers 10 years old | 5 |
In fleet A, faults rise in the same period, the renewal budget is squeezed into one year and the whole fleet can go down together. In fleet B it is known from the start which container is renewed when. A fleet usually ends up like A, because the first investment is made in one go, later additions follow only as need grows and the core stays the same age.
To see the distribution, count containers by purchase year; it is half an hour of work and shapes the budget for the coming years. Two containers of the same age can see different use, so add trip counts and repair records beside the year. A phased replacement programme, or renewing part of the core early, spreads the profile.
