Essentially this article is a huge safety concern. I don't know if it explains it well. Basically ships do not use a grounded systems to get 120V. In your house, you have three hole in the outlet. 1 is hot (usually the left), one is neutral (typically the right), and the other in the bottom middle is the ground. if you stuck your hand in all the holes, only one of the holes would shock you (assuming a proper system- who knows how jacked up your grounds and distribution system may be). This is important to understand, only ONE of the conductors can shock you.
Now, let's say that I'm an electrical component manufacturer, and I want to save money by installing an automatic breaker in the protector (like most have). Why would I ever want to install more than just the one on the hot lead? Why waste the money installing a pointless breaker for the neutral line, when I can electrically isolate the entire strip by breaking the one wire?
Now, here it comes! On a ship, there is no "neutral" line in the traditional sense. In a house, you have a grounded center tapped transformer. Now a ship is a big hunk of metal that rusts quickly. You can't have a ground to the hull of the ship (or the ocean), because the electrical potential in the hull would rust the entire ship. very fast. To mitigate this (along with other, more confusing benefits) ship use an UNGROUNDED system. The consequence of this is that instead of having one line that jumps up from -120V to 120V, you now have two lines that are both -60V to 60V. This is really hard to grasp for some people. The two lines are completely out of phase, and that means that when one line is at +60, the other is at -60 (creating a potential difference of 120V). This is how every outlet on a ship is. If you stuck your finger in a ship outlet, 2 of the holes would give you a shock (albeit a little less painful).
Now, let's take your single breaker power strip on a cruise, and plug your toaster into it. Now remember, that third bottom center prong still exists, solely for safety. Being plugged into a normal outlet (surge protector not in the system), if a hot wire inside your toaster comes loose touches the metal shell of the toaster and you touch the shell, bad day. If the shell is grounded to the hull (connections inside the toaster run to that middle bottom wire), the hull is a better conductor than you, and will dissipate the current, until some grumpy electrician onboard hunts your toaster down as the ground in his system (and the culprit who is rusting the ship).
Now take that same instance and plug your grounded toaster into the power strip into the ship system. Right off the bat, the breaker in the power strip trips (and your ground-wire is touching the tripped hot). There is still half of that 120V bumping around in your toaster. Since you have effectively made a new path (hot wire, to the shell of the toaster, through the ground wire, into the hull), that 60V's worth of current will be traveling through your toaster, and into the hull. This would heat up the toaster, and depending on the location of the ground, could melt things and cause fires. Hope you learned something!