At 80s to overload? With 80% hull? This seems improbable. Are you sure this data as right? Does Katana's HP go down from 80% at a fast, constant rate? That would mean it's self-destructing, and that would in turn mean a SEXP bug. I don't see any better explanation, this is plain weird. Also, try pressing "G" key while targeting the Katana, which will show you the closest ship attacking it.
Hi, after few more trials, I think Katana has 80% hull at 80s to overload is totally possible.
I looked about the amount of damage dealt on Katana.
As pireciter said, beams are all favor Katana over Altan Orde.
There are (exclude Deianira and Iolanthe):
2 Aeolus : 4SGreen (2888 per pulse, 45s recharge)
Carthage : 2 TerSlash (3850 per pulse, 10s recarge)
These beams could deal nearly 20k dmg right after the presence of Katana. Not even to mention TerSlash has only 10s recharge time and I already excluded two major threats.
As the result, it's not improbable, it seems to me this is very likely to happen.