"Can't understand why so many boat owners won't invest in an
inverter, it can't be the expense, and these voltage step-up units are
more
expensive than inverters..."

Most of us that are using laptop computers on boats are using them in
conjunction with an HF radio (ham or marine SSB) to receive weather
fax images, and to send a receive e-mail. Most inverters make noise
on at least some of these HF frequencies when converting AC to DC.
Also battery power on sailboats is precious and even the small
inverters are not very efficient. A small power booster like the one
made by the ham radio operator, Sam Ulbing (N4UAU), are very efficient
and quite. Perfect for this application.