From strange markings on the hull, to how ships are designed, to how passengers are enticed to spend more money onboard, cruise lines have some clever secrets hidden right in plain sight. And if these items aren't pointed out, then it may not even be on your radar.

But when you know what to look for, these cruise secrets can make you a smarter passenger... and maybe help explain some things you've always wondered about sailing.

Here are eight things hidden in plain sight for your next cruise.

Image of First World Hotel: Courtesy of Eqdoktor via Wikipedia under license CC BY-SA 3.0 (https://creativecommons.org/licenses/...)