AI not building ships

[PeterD]

After a fairly long game I decieded to have a look at all the other races to see how they were
handling their resources.

Some had big fleets while a couple of others had
just a few ships despite a LOT of all minerals.

Any ideas why the AI wouldn't build more ships.
Also one race had built only to cruiser level while the Last time I played against that AI it
went much further.

Any help much appreciated.

Peter