Bill writes:

Is it considered copyright infringement to change all the dimensions
on the plans in order to enlarge the boat for personal use?

No one in this thread seems to understand that US copyrights do not protect
designs, only the *expressions* in the plan documents themselves. You can
make your own drawings of the same design, modify the design, build the
design, etc., without regard to copyrights.

Anyone can build a boat in any design they like, including copying existing
designs. The fact that someone drew a design on paper doesn't stop you
from building something.

Copyrights simply do not apply to utilitarian objects. Boats, cars,
houses, furniture, clothes, etc.