I think the problem with a desk top PC on a boat is that they are
power hogs. If a desk top PC uses 240 W, that is 20 Amps at 12 V. That
is a lot of power. If you use an inverter then you also have the
losses of the inverter. I think people use a Laptop because they use
much less power. I personally would love to use a desktop PC because
they are much cheaper and componenets are much easier to replace, but
the power consumptions is preventing me from going that route.
Does somebody have an solution to this problem, ie a desk top PC that
uses the power of a Laptop?

Ahh yes... I see your point

Most laptops are designed to be very frugal with power,
aren't they?

Im like you....Id rather use a small desktop tho.
Maybe someone has developed a line of desktop based on
low power components of laptops?