There are several issues that make PC screens unsuitable for marine use.
There are considerations for power, protection from the harsh enrinment

True, protection against outdoor moisture levels is well beyond what most PC
monitors can deliver. Not to mention they're not very good at displaying in
direct sunlight.

etc., but a real driver that few people are aware of is night viewing. It
is
imperitive that the display dims to black. PC monitors will not.

That's untrue. It's entirely dependent on the application driving the
monitor. If the application program doesn't use the energy star or other
power managment functions then it'd certainly be less than ideal. But in
this day an age very few things remain that defective regarding power
managment.

If you avoid the commercial
certified screens and go with the yacht screens, you will end up with the
marine performance sans certification costs.

+1, great suggestion.

Please also be aware that when interfacing things like black box radars,
be
aware of aspect ratio, not just screen size. If the screen size does not
physically match the resolution to be used, circles appear as ovals and
that
really looks horrible.

If you're running PC applications just make sure your video display card can
drive the monitor at it's native resolution. Most cards can support the
usual 4:3 aspect ratio as well as newer 16:9 and other variants. Check
first, otherwise stick with getting a 4:3 aspect ratio monitor at pixel
resolutions like 800x600, 1024x768 or 1280x1024.

Avoid the automobile screens with only 400 line vertical resolution. That's
fine for presenting a touchscreen FM radio/CD player but it's horrible for
the sort of precision you'd need for chartplotter applications.