Why do people get seasick, and how can you avoid it?

Like in other areas of life, technology is also improving our lives in boating. Over the last years, various stabilization technologies have come available to dramatically reduce the motions that mostly cause seasickness on boats, meaning that even those who are affected by seasickness more than average can enjoy the privacy, comfort, and pleasures in boating. We will investigate these later. Towards the end, I will also share some tips and sound advice, which will reduce the risk of getting seasick if your boat is missing stabilizers. If that's what you came here for, scroll down to the bottom of the page. But first, let's look at what seasickness is and what you can do on board a boat to avoid getting seasick.

What is seasickness?

Seasickness is a form of motion sickness. It is a normal response to a specific motion stimulus, where the individual will feel nauseous and, in some cases, experience unsteadiness. On a boat, it typically appears when a person is exposed to unfamiliar movements, and very few of us are truly immune. In other words, most people will get seasick under the right (wrong) conditions.

Like mentioned, it is provocative motions that induce motion sickness. It is repeated accelerations in the inner ear balance center, generated by the wave's movement of the boat, that cause us to be sick. The faster our body is accelerating in one direction or another, the more likely we are to experience motion sickness. For example, most people will get rapidly sick on the complex accelerations generated by merry-go-rounds, rollercoasters, and so on – or why you are more likely to get seasick in vast seas or swells.

Even a small reduction of provocative motions makes a significant difference

What frequently comes as a surprise to many, is how little of the provocative motions you must reduce to reduce the risk of being seasick considerably. A study performed by McCauley et al. investigated the relationships established between the incidence of symptoms of motion sickness and the frequency, magnitude, and duration of the motions leading to seasickness. The results have later been embodied in the British Standard 6841 and ISO Draft International Standard 2631-1.

Looking at the below graph, you will see that when exposed to rapid movements of the head, with a frequency between 0,83 and 0,42, most people get motion sick. Bla, bla, bla.

In plain English, this means that we get seasick in swells and in waves that make the boat roll a lot with intervals between 6 and 3 seconds. But it also shows that if we can eliminate 70-80 per cent of these effects, which most stabilizers can do, very few people will get seasick.

Example: 

• You are on a boat, which rolls in 4 seconds intervals (0,25 Hz). The acceleration of the boat's movements is rather fast, say 3.3. Exposed to these forces, statistically approx. 70 per cent of the people onboard will get seasick.
• On the same boat, we activate stabilizers and eliminate 80 per cent of the roll. The roll period will still be 4 seconds, but the boat will roll 80 per cent less, which means that the RMS acceleration falls equally. In this case, statistically, approximately 10 per cent of the people on board will experience signs of motion sickness. The reason for this reduction is that we no longer encounter violent accelerations of the head.

We can conclude that by adding stabilizers to a yacht, even during bad conditions, only a fraction of the guests onboard will experience motion sickness.

Which movements are we exposed to on a boat that can make us seasick?

A yacht at sea moves in six degrees of motion – simplified it means that it is free to move up/ down, forward/backwards or right/ left, and its ability to rotate around its three axes. These movements on a yacht are referred to as heave, surge, sway, pitch, yaw, and roll. Simplified, it means something like this (click to expand):

It is these movements that cause us to be seasick, and some are more uncomfortable than others. Today, many of these can be countered using different stabilization technology on the yacht (more on that later).

Notice, however, that different stabilization technologies work very differently, so it is important that you choose wisely. Some are made to work at anchor, whereas others are made for cruising. There are also stabilization systems on the market today, which are made for both at anchor and for cruising stabilization. Regardless of what you choose, make sure you ask for documentation and test reports on the systems actual efficiency both at anchor and underway.

How do we counter the effects of the movements that make us seasick?

Heave and pitch

Heave and pitch movements are reduced as the boat or yacht gets bigger. Typically, a longer boat will have significantly less heave or pitch than a smaller boat. Apart from getting a bigger yacht, it is nothing you can do to remove the heave. However, based on my experience as a yachtsman and former captain, heave is rarely a problem on larger yachts, unless there are heavy seas, in which case we tend to avoid taking guests out on the open sea.

However, pitch can be a challenge, and just as for heave, the pitch is reduced as the boats get larger. But luckily, the effects from pitching can easily be countered by where you position yourself onboard. As a captain, I was very conscious about where I placed the guests onboard. Pitching is something you per definition experience in the bow – or at the stern of the boat, depending on the vessel type and cruising speed. This is where you have the most significant movements, and this is where you see the largest acceleration up or down. So, if you make sure that your guests stay midships, you rarely have any problems. This is also why you usually find the owner's cabin positioned in the center of the boat. So, if you want to avoid getting seasick, stay away from the bow or stern in heavy sea.

Roll – our worst enemy on a yacht and the easiest one to eliminate

A boat that is rolling from side-to-side is uncomfortable and if you’re exposed to heavy rolls, it is likely to make you seasick. It is possible to “hide” from the roll by moving down in the centre and towards the waterline of the boat, but practically speaking; this is not where we want to be when we’re out on the water. Heavy rolls also increase the risk of fall injury for the guests and crew. To avoid seasickness and the risk of injuries for its passengers, cruise ships have been using stabilizers for a long time. Over the last decades, stabilization technology has become a "must-have" on superyachts and yachts down to approximately 60 feet. There are many options to choose from on the market – and they work very differently, so make sure you do your research before you decide which technology to put on your yacht. This might very well be the most important part of the boat's options list (in addition to air-conditioning perhaps).

When a boat is rolling from side-to-side, the rapid and constant acceleration of the head from side-to-side has a significant risk of making most people seasick. How much, and how the boat will roll, depends on the length and size of the waves and the overall stability of the boat.

• Rapid waves don't create much roll. You typically get these in sheltered waters or just as the wind picks up.
• Long, slow waves (typically swells), is what you have in the days following heavy winds. These make the boat roll with the waves, but the boat usually rolls slowly and just follows the wave.
• Unfortunately, the typical waves we encounter at sea, however, have a frequency around the boat's natural roll period. Usually, you have between 3-5 seconds between each wave, and in these conditions, the boat will roll far beyond the effect of the wave. So even if the wave only rocks the boat 5-6 degrees, the inertia energy of the boat, or its momentum to keep rolling, will make it roll much more than the actual angle of the wave. This gives large movements and sudden acceleration and is the perfect recipe for seasickness.

Luckily for boaters, this rolling effect is something we can almost eliminate with today's technology, and compared to the cost of a yacht, it's a relatively small additional cost.

Yaw

When the yacht is maneuvering/steering, it is rotating about it's vertical access. This rotation is called yaw. Like pitching (up/down movement of the bow/stern), this effect is mostly felt in the stern or at the bow of the yacht, furthest away from its rotating point. For comparison, in a car that follows a road that just keeps on turning, this "yaw" effect is what often makes passengers carsick, but as boats rarely need to follow the turns in the same way as a car, the effect is usually a lesser source of seasickness. We do have some advantages at sea!

Worth mentioning regards yaw though, is that a side-effect of some of the stabilization systems on the market is that they create a bit of additional yaw. The yaw effect is considerably more significant on flat fins than on Vector fins. In either case, this side effect, when it comes to eliminating seasickness, is compensated by the stabilizer's ability to reduce roll and dramatically increase overall comfort and safety onboard.

Surge and sway

As mentioned at the beginning of the article, it is repeated accelerations that make us seasick. Hence the yacht's constant movement forward or backward does not make us seasick. Sway is uncomfortable, and you might have experienced it before on trains riding on uneven tracks. The sideways movement of the train has an impact on overall comfort and can contribute to motion sickness. Onboard a yacht with fin stabilizers that generate too much sideways movement, you can experience a touch of sway. How much the stabilizers will move the boat sideways when they counter the roll from the waves depends on the shape, size, and positioning of the fins on the hull. Flat fins, notably positioned towards the center of the boat, creates a significant sideways force. That is why many boaters today choose vector fins, which generate mostly up/down stabilization, reducing the sway effect with up to 50 percent (because they generate much less sideways force).

Stabilization systems onboard modern yachts

My colleague, Ronny Skauen, has written an in-depth article about the various stabilization systems for yachts and what you should consider when selecting yours. You can read the full article here.

In short, there are a few different systems that dominate the market today, and we will look at the pros and cons of the most popular systems below:

• Vector fin stabilizers
• Flat fin stabilizers
• Gyro-type stabilizers

On a yacht without stabilizers, rolling make the balance center (of a person's head) move fast from side to side. On a stabilized yacht, the movements will typically be reduced by more than 80 percent. Since the rolling cycle will be the same, the acceleration, which is what makes us seasick, nearly disappears. 

Stabilization underway – how to not get seasick while cruising

If you use your boat a lot for cruising, there are big differences in the various stabilization systems available on the market today. Here, you really need to pay attention to what kind of system you're putting into your boat. 

You need to know that where gyro stabilizers are restricted by only having a constant force available to stabilize the boat, the stabilizing forces of fin stabilizers increase immensely as the speed of the boat increases. If you have a good understanding of physics, you will know that the forces vary by the square of the speed. Hence, at speed there can be huge differences between the stabilizing forces of a fin system and a gyro.

• Gyro stabilizers have a constant and limited force available to stabilize the boat. Typically, this is not enough to stabilize the roll effects from significant waves or if you ride a long wave. One often, therefore, says that gyro stabilizers are best used at anchor, and if you want to stabilize your yacht underway, it is recommended to add fins or Vector fins.
• Flat fin stabilizers work well at speed, but as mentioned in a previous paragraph, when they generate the force to stabilize the yacht, a side effect is  sway and yaw. The overall comfort on the boat is still dramatically improved, and there is a significantly less chance of getting seasick.
• Vector fin stabilizers are typically smaller than the flat fins, but because of their curved shape, they generate much more lift per square meter – and much less sideways forces (less sway and yaw). Hence you can keep the fin size and dramatically increase the stabilizing forces (without increasing yaw or sway) – or you can reduce the fin size and remove the negative side effects from yaw or sway with approximately 50 percent.

Most people want a stable yacht – at any speed. So which stabilizers are best?

If you have read this far, you probably understand that I am biased in this discussion. I have the privilege of working for the world's leading manufacturer of fin stabilizers for yachts and have a personal interest in promoting the Vector fins. But, if you have a good understanding of physics, the Vector benefit will be self-evident.

With that said, I will argue that there is a big difference between the various systems when it comes to stabilization efficiency and that boaters in general, have a lot to win from being critical when they investigate the various systems.

• Is the manufacturer willing to give you up-front estimates of the roll reduction of the boat both at anchor and during cruising? How about at top speed? Or are you just getting at anchor estimates?
• Will he let you know how you can expect the system to stabilize the yacht in various sea conditions? How much stabilizing force do you have available? Which system will give you the most stabilizing forces (and least side-effects)?
• Has the manufacturer got the experience and service network needed to help you plan the fins' perfect positioning on the hull and service you afterward?

The Vector Fins from Sleipner Motor has been installed on the majority of the world's yacht and superyacht brands and has a proven track record for being super performant. Many of the world's most known yacht producers have chosen Vector Fins as their standard stabilization system because they know it is a safe way to get happy customers. There are also several other advantages with the Vector fins, for instance; reduced drag compared to old-style flat fins and their ability to create lift, frequently resulting in a reduction of fuel consumption and an increase in top speed. However, this article is about how to prevent seasickness, so let's stop at that.

How to prevent seasickness without stabilizers?

Based on my experience at sea, of which many years have been spent taking guests out daily, there are several things you can do to reduce the risk of getting seasick:

• The most effective advice I can give you is to make sure you can always see the horizon. This gives your brain a point of reference, allowing it to sense the motion of the yacht and your body's movement with it.
• Stay as close as you can to the boat's pivoting points (remember the drawing showing pitch, yaw, and roll?). Practically speaking this means:
• Position yourself midships. Stay away from the bow or stern (they tend to move up and down)
• Stay away from the flybridge (side-to-side roll is much more aggressive than further down on the yacht)
• In a modern yacht, you most often have large windows in the master cabin, allowing you to see the horizon. If you lie down for a bit and look out the windows, you are usually at the center of all the pivoting points of the boat and will experience minimal effects from roll, pitch, or yaw. Most people will rapidly feel better.
• Balance your diet. Eat some light food, but don't overeat. Try a ginger ale (or something containing ginger). Avoid greasy food, smelly food, acidic food, and spicy food.
• Make sure you are well hydrated. Dehydration is a quick pathway to seasickness. Drinking water is good for you. A coke might also help, as it has some of the same ingredients as you find in anti-nausea drugs.
• Take it easy on the alcohol – it has never been a good cure for nausea...
• Get some fresh air – and avoid smelly areas (cooking, exhaust...)
• You can take various types of medications that reduce motion sickness. Consult your local pharmacist.
• Stay away from other seasick guests... one guaranteed way to get seasick is by observing other seasick people.
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If you skipped the first part about how stabilizers can cure seasickness, you can jump back up and read about the reasons behind why people get seasick, and how stabilizers can eliminate the problem. 

Boating should be comfortable, and you're not comfortable when you're seasick. I hope this article has given you some insight into why some people get seasick, how you can avoid it, and why we confidently claim that Vector fins are the permanent cure for seasickness.

Have a fantastic boating season, and if you're considering stabilizers, feel free to reach out and contact us.