While doing some research on APC uninterruptable power supplies, I was browsing their knowledge base when I discovered this surprising note:
In North America, one would expect to see approximately 120 volts when measuring from hot to neutral and from hot to ground. However, larger ships use delta power. That is, there are two hot legs (center tapped 120Vac) and a ground: no neutral. Each hot is 60 volts. One can measure from hot to hot (phase to phase) and will see 120 volts. When measuring from either hot to ground, one will see 60 volts.
It’s been a long time since I understood exactly how AC power works, but you can read the full article for the gory details. (Don’t forget to read up on the corollary as well: Never use Smart-UPS X93 Shipboard series with land power.)