Merchant Hulls

I've always been under the impression that Merchant hulls
are always considered to have four rows of damage boxes.
Tried to double check this today, and the only rules I
can find seem rather vague. They mention that all Merchant
ships are of the same class, regardless of size, but only
seems to list the required number of rows for the military
classes.

It makes sense that they'd be more susceptible to threshold
checks (fewer redundant systems), but I'm no longer sure
that I'm right.

Any ideas anyone?

-- 
Be seeing you,					     ARM not Intel.
Sam.					       Acorn not Microsoft.