Hi Lloyd,
From the sounds of it you have quite a substantial amount of faith in
the strength of aluminium hulls. To compare aluminium commercial fishers
with "backyard skiffs" is somewhat akin to comparing apples and hammers
though wouldn't you agree?
Heres a little challenge to affirm or refute your faith in those riveted
hulls you can try if you're ever bored and have a little jalopy you don't
care much about. Word to the wise though, do not try this far from shore.
Take a large piece of firewood, spray paint it neon orange for
visibility and float it in the water. Back track a ways and ram it full
speed, in similar fashion an unsuspecting boater might accidentally hit a
similar piece of driftwood while underway. Try to ensure you reach it doing
cruise speeds (20-30 mph).
Until you actually see what this type of an impact does to a "backyard
skiff," holding them to such false high esteem would lead one to believe
they are safer then they really are. I have proof to give me reason to
believe otherwise. Okay okay I know it doesn't happen every day, but it does
happen, it happened to me so it could just as easily happen to anyone.
Perhaps aluminium hulls don't mind being "dragged over rocks and gravel"
when being beached, but then again neither does my canoe. It, however, is a
far cry from the security I feel when bumping something unexpectedly in my
fibreglass hull (to a point). I still say glass is the way.

regards
Bryan