How Deep Does the Water Have to Be for a Cruise Ship?

Anyone who’s ever seen a cruise ship in person will tell you that those colossal watercrafts are nothing short of a modern marvel. But with the cautionary tale of the Titanic etched in our collective consciousness, some people might feel apprehensive about stepping aboard a modern-day cruise ship that’s twice the size of the infamous titan.

All of that said, you might find yourself wondering - how deep does the water have to be for a cruise ship? And could those things possibly tip over if the water underneath just gets a little too shallow? Here’s everything you need to know.

How Deep is the Water Under a Cruise Ship?

Now, the answer to this question isn’t really etched in stone. In fact, the numbers can actually change drastically depending on the size and the weight of the ship. Interestingly enough, the weight of a cruise ship can actually change between docking and departing, thus the depth of the water may also have to be reconsidered.

In general though, the water under a cruise ship has to be 25 to 50 feet deep. Keep in mind though that it may have to be slightly deeper than that. This takes into account the ship’s draft which is essentially the measure from the waterline along the side of the cruise ship to the lowest point of its hull.

A cruise ship with a hull that extends 25 feet into the water will need the water to be slightly deeper than that to prevent its hull from scraping the bottom. On average though, an allowance of 10 feet or thereabouts should be more than enough to accommodate the ship’s weight.

Remember though that ships tend to dip a little lower into the water when there are passengers on board. So while 35 feet of depth might be enough to accommodate an empty cruise ship that extends 25 feet into the water, it might need more allowance once the passengers start boarding.

How Deep is a Cruise Ship Underwater?

More than half of the ship (or essentially the part of a cruise ship you can actually see) is where you’ll find all of the guest amenities and staterooms that are available for cruise guests to visit. Below that are utility rooms and spaces that they like to keep out of view since they’re not really necessary for passengers to visit.

To mix things up a little though, there are some cruise ship liners that offer underwater rooms. No doubt, this can be a bit daunting. But the strange new views and the risky appeal definitely lures in guests who want a new perspective on the good old cruise ship format.

It’s important to keep in mind that the amount of ship that goes underwater depends on the weight it carries. That said, a cruise ship should be much less submerged when it’s empty as compared to when it’s full of passengers at full capacity.

Another thing that dictates how deep a cruise ship will be underwater is its displacement. This basically pertains to the amount of water it pushes out of the way so it can move forward. The deeper a cruise ship dips into the water, the higher its displacement have to be. For reference, some of the biggest cruise ships will displace about 100,000 tons of water as it moves forward to keep the vessel afloat and upright.

What Percentage of a Cruise Ship is Underwater?

cruise ship in water

So, exactly how much of the ship actually goes underwater? Well, again, the answer varies. Cruise ships come in varying sizes, so the measure of the draft can change from ship to ship. In general though, there’s about 40% of cruise ship underwater that you can’t see.

That means whatever you see above water usually only accounts for 60% of the ship’s entire size. Remember though that some ships can have more or less than 40% under the waves. But in general, the amount of ship underwater rarely ever exceeds 50% of its actual size.

Why Don’t Cruise Ships Tip Over?

With such colossal size and hefty weight, the common notion is that cruise ships struggle to float. But if that were true, then they wouldn’t exist today. In simple terms, cruise ships float because they displace the same amount of water versus how much it weighs.

To achieve this, engineers who designed the cruise ship compensated for the minimal draft by giving cruise ships an extra wide hull. This helps the ship displace more water so that it can compensate for its size and weight. In the maritime world, this type of hull is called a ‘displacement hull’ and is typically found on larger vessels like cruise ships, freighters, and naval vessels.

Another reason why cruise ships aren’t likely to just give up and sink or tip over is because they take weight distribution into careful consideration. The heftiest weight on the ship is placed at the bottom of the hull.

This is opposed to placing it somewhere towards the center or the top of the ship’s height which would make it vulnerable to tipping over under moderate winds. But what about when it’s fully loaded with guests? Well, they took that into consideration too.

You’ll notice that the different features and amenities on a cruise ship try to spread people out across the available space. This allows cruise ship operators to prevent people from congesting just one area, thus making the ship more balanced in general.

Bon Voyage!

While memories of the Titanic can haunt even the best of us, cruise ships of today are far more stable and reliable than how they were built way back when. So there’s really no need to worry. Nonetheless, if you were wondering how deep does the water have to be for a cruise ship, this quick explainer should clear up the smoke and help you feel a little less apprehensive about booking that three day cruise.