I did some consulting for US Marine near Seattle. The same people who
design Bayliner also design Maxum. The same factories and workers are
used, and I believe the same molds, etc are used.

The same molds are not used.

For example; compare the 18-foot Maxum with the 18-foot Bayliner

Maxum:
LOA is 17'6"
beam is 7'
hull draft is 18"
deadrise is 19 degrees
weight is 2000 pounds.

The Maxum is built with an interior fiberglass liner, consistent with the
"three piece" construction technique used by many builders. (hull, interior
liner, deck).

Comparable 18-foot Bayliner:

LOA is 18' 0"
Beam is 7'6"
Deadrise is 17 degrees
Weight is 1878 pounds
Hull draft is 14"

Clearly *not* the same mold.

Rather than an interior fiberglass liner, the Bayliner uses "XL composite
panels" with a "lifetime limited guarantee against rot in hull, deck, and
upholstery components."

Some of the weight difference may be due to the difference in standard engines.
The Bayliner has a 90HP outboard as the standard engine, while the Maxum is
standard with a 3- liter stern drive. Once again, not the same mold at all.