Why is it not easy to get seasick on luxury cruise ships?

Cruise tourism is very popular in developed countries in Europe and America. Now China has cruise ports in Tianjin and Shanghai, and some famous cruise companies also take Shanghai and Tianjin as their home ports. Different from ordinary passenger ships, cruise ships aim at providing pleasure to tourists, and the experience includes two parts: the route and the facilities of the cruise ship itself. A cruise ship is equivalent to a hotel at sea. In order to provide better service, the number of crew on cruise ships is far more than that of ordinary passenger ships, and the number of crew on some luxury cruise ships will even exceed the number of guests. Since you want to experience the life like a luxury hotel on a luxury cruise ship, seasickness is something that tourists can't feel, so that you can eat well, sleep well and have fun at sea! So why can't you experience the seasickness of ordinary passenger ships on cruise ships?

What is seasickness?

Seasickness is one of the most common maritime diseases. When riding a vehicle, people's position often changes. When these changes exceed the adaptability of some people's balance organs, or exceed the tolerance threshold of the vestibular system of the inner ear, the vestibular nerve function is temporarily disordered. In addition, some people may get carsick, seasickness or airsickness, which is medically called carsickness.

For example, when sailing at sea, the abnormal motion caused by the turbulence of cruise ships often produces various acceleration stimuli. When the stimulation is too strong or the stimulation time is too long and exceeds the tolerance threshold of vestibular system (everyone's tolerance threshold is different), motion sickness will occur. At first, the symptoms of motion sickness include dizziness, head swelling, headache, nausea and vomiting, followed by pallor, palpitation, chest tightness, cold sweat, cold hands and feet, and weakness of limbs. In severe cases, you will faint, your pulse will slow down and your blood pressure will drop. If vomiting is frequent, mild dehydration, sunken eyes and general weakness may occur. Dizziness, fatigue and nausea are typical symptoms of carsickness. Sleep syndrome shows fatigue and tiredness, and is also considered to be related to motion sickness. If the nausea caused by the shaking of the ship is not relieved, patients will vomit frequently, but unlike ordinary diseases, the nausea caused by motion sickness will not be relieved after vomiting.

Why do people get seasick?

Our ears can help us keep our balance. In the structure of human inner ear, there are three semicircular canals similar to snail tentacles, which are called semicircular canals. There are also endolymph in semicircular canal, and hair cells in both bony feet of semicircular canal. Therefore, when the inner lymph flows, it will also drive the hair cells to bend and fall off, resulting in the feeling of movement. The semicircular canal is mainly stimulated by the acceleration of the positive and negative feet, that is, the change of rotational motion. Because the planes of the three semicircular canals are perpendicular to each other, you can feel the stimulation of rotating motion in all directions. When the head moves, the liquid flows, and the receptor sends a signal to the brain that the position of the head changes. So the brain gives instructions to ensure the balance of the body.

Ear structure

The balance of human body mainly depends on the coordination of vestibule, vision, muscles and inner ear joints. Among them, vestibular system of inner ear is the most important. Its functional structure is actually like an eye. It is a specially differentiated receptor, which mainly senses the head position and its changes. How do people feel if they do linear motion? It depends on the balloon and oval sac in the vestibule of the inner ear. Balloon and oocyst also have endolymph and hair cells, as well as otolith membrane. When people do linear acceleration, the potential sand in the otolith membrane will move in the opposite direction, just like the stone in the bottle. When shaking the bottle to the right, the stone will roll to the left of the bottle, and when shaking the bottle to the left, the stone will roll to the right of the bottle, thus stimulating the hair cells to feel balanced.

Human sensory organs have a range of perception. For example, the range of audio that the human ear can hear is 20HZ~20KHZ, and it is difficult for the human ear to feel it below 20HZ or above 20KHZ. And living in an overclocking environment for a long time can easily lead to irritability. Similarly, the balance system dominated by the vestibular system of the inner ear also has the maximum limit that can withstand stimulation, that is, the threshold. Different people or different periods of a person have different thresholds according to their physical condition. Exceeding the threshold that the human body can bear will lead to the disorder of the balance system and seasickness.

Why is it not easy to get seasick on luxury cruise ships?

Ship rocking is the most important factor of seasickness, and it is also the biggest test for cruise ships to prevent seasickness. At present, in addition to speed, the most important thing in the hull design of cruise ships is to resist complex sea conditions, so as to minimize ship shaking and maximize comfort. In the dynamic balance state of the ship, increase the width of the ship, increase the freeboard height, reduce the height of the center of gravity, reduce the wind pressure side arm, increase the intake angle and reduce the rolling angle.

Schematic diagram of hull stability

The hull itself is in dynamic equilibrium. The stability considered in the design is that the ship leaves and tilts under the action of external force. When the external force is removed, the ship can recover to its original equilibrium position. The basic principle is shown in the above figure. When the ship is subjected to the heeling moment Mh, it floats to one side with an inclination angle θ (θ≤ 100 ~ 150), and the waterline moves from WL to W 1L 1. After tilting:

1. the force w is constant because the weight does not increase or decrease during the tilting process;

2. The position of the center of gravity G remains unchanged, because no heavy objects move during the tilting process;

3. Buoyancy D is constant, because the weight is constant, so the displacement is constant;

4. Only the position of the floating center B changes due to the change of the shape of the drainage body, from the original oblique side of B to B 1.

Due to the buoyancy of water, restoring moment Ma will be generated which is opposite to the heeling moment Mh, and the ship will return to the equilibrium position.

Stability can be divided into lateral stability and longitudinal stability according to different tilt States; According to the different dip angles, it can be divided into initial stability and large dip stability; According to whether there is angular acceleration when tilting, static stability and dynamic stability are divided. According to whether the cabin is damaged or not, it is divided into complete stability and damaged stability. The stability of cargo ships changes greatly with the change of the center of gravity and the position of floating center of cargo handling, and so does the stability. Generally, the center of gravity and buoyancy of cruise ships have not changed much, and its stability is considered to be basically stable.

Hull shaking is the most important factor of seasickness, and it is also the biggest test for cruise ships to prevent seasickness. At present, in addition to speed, the most important thing in the design of cruise ship hull is to resist complex sea conditions and build a cruise ship with the least shaking and the highest comfort. In the dynamic balance state of the hull, increasing the hull width, increasing the freeboard height, reducing the height of the center of gravity, reducing the wind pressure side arm, increasing the intake angle and reducing the rolling angle can all improve the seakeeping of the hull.

Seakeeping refers to the ability of a ship to overcome waves and other movements. In order to improve the seakeeping of ships, so as to reduce the shaking amplitude and change the shaking period, which is the key purpose to realize the comfort of ships, anti-rolling equipment is usually installed on ships:

1. catamaran design

Many high-speed cruise ships you see are catamarans. Generally speaking, it is to connect two hulls, generally equipped with double propellers and double rudders, with good handling performance. The design of catamaran greatly improves the floating center and reduces the center of gravity. The distance between the center of buoyancy and the center of gravity determines the stability of the ship, so the stability of this kind of ship is greatly improved, and the swing is smaller than that of a single ship, which increases the riding comfort of the crew and reduces the probability of seasickness. At the same time, there is no need to install "stabilizer" equipment, which also reduces the purchase cost.

Catamaran design (New Zealand Maritime Technology Co., Ltd.10.6m catamaran design)

2. Install bilge keel

Stern keel is the most widely used and simplest anti-rolling device. It is installed at the stern of the ship along the captain's direction, which disturbs the flow field around the hull during rolling and makes the ship generate additional damping, thus increasing the rolling damping and achieving the purpose of reducing rolling. It is effective in all sea conditions, especially when the ship periodically rolls and waves periodically act. The only drawback is that the stern keel will slightly increase the resistance of the ship. Because of simple structure, low construction cost and little influence on speed, almost all seagoing ships are equipped with bilge keel, which has become a part of seagoing ship hull. So in general, the so-called anti-rolling device refers to anti-rolling measures and equipment other than bilge keel.

Ocean Oasis

3. Install the fin stabilizer

Fin stabilizer is one of the most popular anti-rolling devices in the world. In the process of ship rolling, the angle of fin stabilizer relative to the water flow is automatically adjusted by the control mechanism, so that the left and right fin stabilizers produce the maximum torque opposite to the rolling direction, and the rolling effect is achieved. This anti-rolling device has a good effect, especially suitable for high-speed passenger ships. It is an active anti-rolling device with good anti-rolling effect and wide application. Fin stabilizer first appeared in 1889, and was patented by JohnI.Thomeyeroft. In 1923, Nobutaro Beam Element of Japan designed the first set of fin stabilizer, and achieved good anti-rolling effect through loading test. 1935, the fin stabilizer designed by British Brown Brothers Company was successfully applied to a 2200-ton channel ferry, and it has been widely used since then. The working principle of fin stabilizer is as follows:

The violent rolling of a ship is a vector synthesis of six motion states: rolling, pitching, heaving, bowing, drifting and drifting. Among them, rolling is the most important factor affecting the stable navigation of the ship, and the function of fin stabilizer is to reduce the swing of the ship when sailing in heavy waves, so as to effectively control the navigation attitude of the ship. Fin stabilizer is the only active fin stabilizer widely used at present. Its working part is a pair or several pairs of wings that extend out of the outboard. According to the contractibility of its fins, it can be divided into telescopic and fixed types. Turn around your own axis when you work. According to the theory of fluid mechanics, when the fin moves relative to the current, it will produce a force perpendicular to the wing surface, which is the basic principle of fin stabilizer. The reason why the fin stabilizer can reduce rolling is precisely because it can resist the impact distance of waves through the stable torque obtained by one or several pairs of controlled rotating fins in the water flow, thus reducing the rolling of the ship and improving the seaworthiness of the ship.

With the rapid development of control technology in recent years, fin stabilizer has become the most commonly used and successful anti-rolling device, but the anti-rolling effect of fin stabilizer is proportional to the square of speed. Only when the speed of the ship is high, the fin stabilizer can effectively reduce the rolling, but when the ship works at zero speed or low speed, the fin stabilizer cannot effectively reduce the rolling.

China State Oceanic Administration "Haijian 5 1".

4. Install the anti-roll box

Compared with fin stabilizer, it needs high speed to play its role, and the anti-rolling tank is not affected by the ship speed. Its working principle is that there is a water tank connected left and right in the hull. When the ship swings, the water in the water tank swings back and forth from one side to the other. By designing the cross-section size of the connecting pipeline and controlling the water level difference between the two sides with the adjusting device, the weight difference of the water in the left and right water tanks will generate a moment opposite to the rolling direction, so as to reduce the rolling.

The anti-rolling tank can be divided into three types according to its working mode: passive, controllable passive and active. Passive anti-rolling tank works according to the principle of double vibration and has good anti-rolling effect in harmonic rolling area. It is widely used because of its simple structure, low cost and easy maintenance. With the rapid development of control technology, controllable passive anti-rolling tank is a kind of anti-rolling device and an important improvement of passive anti-rolling tank. It comprehensively considers the relationship between expensive fin stabilizer and passive anti-rolling tank. The control system consumes less power and has the characteristics of automation, small occupied space, simple operation and high reliability. In addition, the controllable passive anti-rolling tank can be used to resist rolling and detect stability, which is the development direction of passive anti-rolling tank at present and has broad application prospects and research prospects. Passive anti-rolling tank works by the inherent period of the tank itself. When there is a big difference between the actual wave period and the natural period of the tank, the tank often fails to achieve the expected anti-rolling effect, and may increase rolling in some sea conditions. The disadvantage is that it occupies a considerable volume in the hull, and its free surface always reduces the height of the ship's pitching center and reduces the initial stability of rolling. Active anti-rolling tank has the advantages of fast response and speed, but it is rarely used because of its high cost, complex system and high power consumption.

Automatic balance control system (note)

5. Application of rudder anti-rolling technology

Rudder anti-rolling is a new anti-rolling technology. In fact, the ship's rolling is caused by the changing forces and moments exerted on the hull by external forces such as wind and waves. However, when steering, the hull will also roll, that is, steering can not only produce the first rolling moment, but also produce the rolling moment at the same time. Therefore, most luxury cruise ships are equipped with bow thrusters, or if the relationship between the rolling torque generated by the rudder and the wave disturbance torque can be correctly controlled, then the rudder can also be used as an anti-rolling device to reduce the rolling of the ship.

Compared with fin stabilizer and anti-rolling tank, rudder anti-rolling device has many advantages and has been paid attention to in many countries to varying degrees. It can make use of the existing rudder and steering system on board, not only for large and medium-sized military ships, special ships and civil ships, but also for small ships. The requirements of rudder roll stabilization for dynamic characteristics of control system and hydrodynamic characteristics of ships are generally easy to meet, so it has a very broad application prospect.

6. Psychological factor control

In addition to the design of the above ship anti-rolling device, in order to ensure the comfort of tourists, there must be no noise, vibration and large-scale shaking in the guest room. To this end, some cruise ships use electric propulsion to avoid excitation and noise of the main engine; Through the reasonable planning of the space scale in the cabin of cruise ship, people can sit and lie more comfortably and reduce the degree of seasickness; Carefully design the air conditioning system to ensure that there is no air conditioning noise indoors and that fresh air is input into every corner of the ship; The factors leading to seasickness can be alleviated to some extent through the coordinated design of cabin colors and psychological measures to relieve passengers' emotions.

Cruise is the main means of transportation for sea passengers to travel and relax in the future, and people's demand for luxury cruise comfort is getting stronger and stronger. Therefore, for the design of cruise ships, how to reduce seasickness from the cruise ship itself through modern technology has been gradually considered.

Note: Xu Anjing and Tan Yue, Research on Automatic Control Design Scheme of Ship Balance Control System, China Ship Repair, No.3, 2005.