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What is the maximum size a ship can become without negating the effects of waves to the point where seasickness is no longer a problem? The larger a ship becomes, the smaller the rocking effect waves have on it becomes. As a result, large ships tend to have a lesser effect on people inclined to seasickness.

So, the question is: How large can a ship become before it becomes extremely unlikely for a person only moderately inclined to seasickness to become seasick, during sea state 4 water? A good answer will address multiple types of ship (e.g., an ocean liner vs an aircraft carrier vs an oil tanker), and how the directions of waves will affect the seasickness of the passengers.

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    $\begingroup$ How big are the waves? $\endgroup$ – Dubukay Dec 3 '17 at 3:34
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    $\begingroup$ If you answer @Dubukay 's question in terms of sea states it will help make our answers all more consistent. Plus, a lot of existing material uses those sea state numbers. $\endgroup$ – Cort Ammon Dec 3 '17 at 3:50
  • $\begingroup$ There are too many variables in this question. How seasick is "seasick" and when is it "a problem"? What's "moderately inclined"? What weather conditions do you expect? $\endgroup$ – Philipp Dec 3 '17 at 4:22
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    $\begingroup$ Not crucial but might be relevant - what type of ship are we talking about here? - there are very different design consideration for commercial freighters, naval warships and pleasure cruise ships. These consideration may "trump" making the ride more pleasant, even for large sized crafts (so you can have a smaller cruise ship giving you a much smoother ride than a larger destroyer, for example - as the cruise ship isn't designed for lower profile, higher speed etc. etc.) $\endgroup$ – G0BLiN Dec 3 '17 at 10:26
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    $\begingroup$ The funny thing is, there is also a minimum size. People tend not to get sick in really tiny boats. I think it is because the waves have a very direct influence on the moving of small boat, kind of like a car with a really stiff suspension compared with a car with a really soft one $\endgroup$ – Ezra Dec 3 '17 at 10:34
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There's a huge variation in ships.

It's not JUST about size, it's about design...angles matter in a big way.

And so too does movement through the water. As long as the boat is moving forward, seasickness is actually less likely. It becomes more of an issue if the boat is not moving, and simply bobbing up and down. The direction that the boat is moving in relation TO the waves is also an issue.

You also have to take into account stabilizers. Most large passenger ships today have them.

Then, you also have to take into account WHERE on the ship you are. Different parts of the ship will experience these things differently.

If you tend to get seasick, cabin location is really important. It's a question of engineering, really. The lower and more central you are in a ship, the less roll and sway you will feel. Even if you choose a balconied stateroom, choose the lowest level and the most midship one you can find. The higher decks and cabins at the very front (forward) or back (aft) of the ship will rock and roll the most.SOURCE

The average cruise ship has a tonnage of 110,000 and length of 952 feet.

First, let's define "moderately inclined" to seasickness and "not unusually rough water."

Let's say we've got a World Meteorological Organization sea state code of 3. That would be 1 ft 8 in. to 4 ft 1 in. So 4-foot waves would not be felt on a ship this large. All of the other factors have to be taken into account, but... 4-foot waves are NOTHING to a boat this large. In my experience, 7 footers aren't much of a problem most of the time either. When it gets to 10-15 ft, you'll feel it, but again, this really depends on a) if the ship is moving and how it's moving in relation to the waves b) where you are on the ship and c) stabilizers (in some cases the stabilizers made it more of a slow roll, which can actually make things worse in some parts of the ship).

I would say that I am moderately inclined myself, but this not only depends on all those factors, but also what and how much I have eaten, and how hydrated I am to begin with (something that should be taken care of days before).

So the answer is It depends on a whole host of factors, and how you define moderately inclined, and what "not unusually rough water" means EXACTLY. There is NO MAX size for this.

“There’s no way to prevent motion sickness 100 percent,” says Dr. Art Diskin, Royal Caribbean Cruises Ltd. Global Chief Medical Officer. SOURCE

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  • $\begingroup$ Also, it depends on what you are doing on the ship - taking fresh air on an open deck or lying in a bed/hammock makes for a less severe experience. Sitting in a stuffy room (or worse, e.g. an engineering section filled with grease and exhaust vapors, or the pantry/kitchen), reading or staring at a radar/computer display for hours, tends to induce sickness even in calmer conditions. $\endgroup$ – G0BLiN Dec 3 '17 at 10:20
  • $\begingroup$ You may want to edit, as I've defined the sea state as 4. 3 is close enough, but 4 would be preferred, although you did mention variously sized waves later in your answer. Sorry about that, there's obviously a lot I didn't know on this subject. $\endgroup$ – Gryphon Dec 3 '17 at 16:25
  • $\begingroup$ @Gryphon Even at 8 ft, on the larger boats with stabilizers, it mostly isn't an issue. I can edit, though it might be a while before I get back to it... $\endgroup$ – Erin Thursby Dec 4 '17 at 4:03
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    $\begingroup$ Apart even from design and angles, resonance is important too. Mathematically, if the wave amplitude matches the pendulum length between the center of bouyancy and center of mass of the cross sectional area of the ship in a plane parallel to both the wave direction and the radius of the earth, then you will have resonance amplified rolls, and that can cause some serious sea sickness. $\endgroup$ – kingledion Dec 4 '17 at 19:41
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I would say that you can get seasick on any size ship. However, the bigger the ship, the bigger the waves have to be.

I can speak from the personal experience of traveling across the Atlantic on a 650-foot ocean liner as a teenager (this one). On the first day out, we encountered some rough water. Maybe 30-foot waves, hitting at about a 45-degree angle on the bow. The ship would rear up, leaning to port, and then flip over to lean to starboard and plunge downhill. It felt like going on a roller coaster I couldn't get off of. Eight of my family of nine got seasick (my dad was in the Navy and had no trouble at all).

I was walking down a hall, wondering when it would end, when I heard the sound of water crashing. I went to investigate, and found the swimming pool. A four-foot wave was running from one end of the pool to the other, smashing against the end of the pool, and then another one. I got in, and the seasickness was immediately gone.

So, if you're ever on a cruise and you get seasick, get in the pool. The ship will move around you.

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  • $\begingroup$ yes, I got a pass to the spa pool for just this reason. and because I did not want to deal with lots of little kids and pool noodles. $\endgroup$ – Erin Thursby Dec 3 '17 at 5:31
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The size of the vessel has less effect on the amount of motion experienced by passengers than the orientation of waves versus the direction of travel of the vessel. Thus a relatively small vessel encountering a large swell head-on can (and from personal experience does) feel far more stable than a large ferry being hit by a very small swell at a 45 degree angle to the prow. Being hit "abeam" AKA either directly from Port or Starboard tends to be the worst.

I'm reasonably prone to motion sickness and one of the worst experiences I've had with seasickness came from a tiny swell (less than a metres) hitting a car ferry abeam on a fine day. The worst day I've travelled on was on the same ferry in a storm so bad they closed the ferry crossing behind us (and the road behind the bus the next morning too) but we were travelling straight into it and were able to sleep through the trip.

Given those two experiences I'm inclined to believe that there is no size limit to a ship built in the long linear tradition that would remove the influence of swells coming in abeam. As for waves hit head-on, they can be unnoticeable in surprisingly relatively small vessels.

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It's simply not possible to come up with a figure.

Between the differences in ship design - hull shape will affect this, but so will stability measures (such as fins and anti-roll tanks) - the way that the vessel is being used (is it stationary, is it moving parallel or perpendicular to the waves) and how heavily is it loaded there are already too many things to calculate.

Add into that the question of how much movement is needed to become seasick - my sister-in-law once became motion sick in a branch of Ikea - and you have no chance.

There is generally a correlation between ship size and a decrease in motion sickness, but that's about as far as you can get.

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