Pg 130 Techmanual
Airships: The Structural Integrity Value for an Airship Support
Vehicle must equal the Airship’s Safe Thrust Rating or 2 percent of
the Airship’s weight in tons (rounded down), whichever value is
higher.
Its the Rounded Down that causes a problem. An Airship with a thrust of Less Then 1 and weighing Less Then 50 tons would have it's Structural Integrity rounded down to Zero.
I'm Fairly sure units with zero structure tend to cease existing.
Is it safe to assume there is an implied "To a minimum of 1" attached to that rule?