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

Cruise tourism is very popular in developed countries in Europe and the United States. Now there are cruise ports in Tianjin and Shanghai in my country, and some famous cruise companies also use Shanghai and Tianjin as their home ports. Cruise ships are different from ordinary passenger ships. They aim to provide tourists with enjoyment. The experience includes two parts: the route and the facilities of the cruise ship itself. A cruise ship is equivalent to a hotel on the sea. In order to provide better service, there are far more crew members on the cruise ship than on ordinary passenger ships, and on some luxury cruise ships, the number of crew members may even be greater than the number of guests. Since you want to experience life like a high-end hotel on a luxury cruise ship, tourists should not feel seasickness, so that they can eat well, sleep well, and have fun at sea! So why can’t you experience the same seasickness on a cruise ship as on an ordinary passenger ship?

What is seasickness?

Seasickness is one of the most common nautical illnesses. When riding a vehicle with significant bumps or violent lifting or rotation, the human body's position changes frequently. 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 disrupted, and the vestibular nerve function is temporarily disrupted. During the journey, some people may suffer from motion sickness, seasickness or airsickness due to adverse stimulation of their sense of vision and smell, as well as vibration of internal organs and other factors. Medically, it is collectively known as motion sickness, which is a disease of balance imbalance.

For example, when sailing at sea, abnormal movements caused by the bumps of the cruise ship often produce various acceleration stimuli. When the stimulation is too strong or the stimulation time is too long, it exceeds the tolerance threshold of the vestibular system (everyone’s tolerance threshold). (different limits), kinesia will occur. Symptoms of motion sickness begin with dizziness, bloating, headache, nausea, and vomiting, followed by paleness, palpitation, chest tightness, cold sweats, cold hands and feet, and weakness in limbs. In severe cases, you may faint, your pulse may slow down, and your blood pressure may drop. If vomiting is frequent, you may experience mild dehydration, sunken eye sockets, and general weakness. Dizziness, fatigue and nausea are typical symptoms of motion sickness. Lethal syndrome, characterized by fatigue and exertion, is also thought to be related to motion sickness. If the nausea caused by the rocking of the ship's hull is not relieved, the patient will vomit frequently. However, unlike other illnesses, the nausea caused by motion sickness will not be relieved after vomiting.

Why do people get seasick?

Our ears help us maintain balance. In the structure of the human inner ear, there are three semicircular tubes like snail antennae called semicircular canals. There is also endolymph in the semicircular canals, and there are hair cells in the two bony legs of the semicircular canals. Therefore, when endolymph flows, it will also drive the hair cells to bend and tilt, creating a feeling of movement. The semicircular canals mainly feel the stimulation of positive and negative foot acceleration, that is, they are affected by changes in rotational motion. Since the planes of the three semicircular canals are perpendicular to each other, you can feel the stimulation of rotational movement in all directions. When the head moves, fluid flows and receptors send signals to the brain about the change in head position. The brain then issues instructions to ensure the body's balance.

Ear Structure

Maintaining balance of the human body mainly relies on the mutual coordination of the vestibular part of the inner ear, vision, muscles and joints. Among them, the vestibular system of the inner ear is the most important. Its functional structure is actually like the eyes. It is a specially differentiated receptor that mainly senses head position and its changes. If a person does forward, backward, left, right, and straight movements, how do they feel it? It is based on the saccule and utricle in the vestibule of the inner ear. The saccule and utricle also have endolymph and hair cells, as well as otolith membranes. When a person accelerates in a straight line, the positional sand in the otolith membrane will move in the opposite direction. The principle is the same as the pebbles in the bottle. When the bottle is shaken to the right, the pebbles will roll to the left of the bottle. Shake the bottle to the left. When using the bottle, the stones will roll to the right side of the bottle, thereby stimulating the hair cells to produce a sense of balance.

The human body's sensing organs have a range of perception. For example, the audio range that the human ear can hear is 20HZ~20KHZ. It is difficult for the human ear to detect audio frequencies below 20HZ or above 20KHZ, and people live in overclocked environments for a long time. In such an environment, the human body is prone to irritability. Similarly, the balance system dominated by the vestibular system of the inner ear also has a maximum limit that it can withstand stimulation, that is, a threshold. Different people or different periods of a person have different thresholds based on their physical condition. Exceeding the threshold that the human body can withstand will cause balance system disorders, which will lead to seasickness.

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

Ship rolling is the most important factor in causing seasickness, and it is also the biggest test for cruise ships in terms of preventing motion sickness. At present, in addition to investing in speed, the most important thing in cruise ship hull design is to resist complex sea conditions and create a ship with minimal rocking and maximum comfort. When the ship is in dynamic balance, the ship width is increased, the freeboard height is increased, the center of gravity is lowered, the wind pressure side moment arm is reduced, the water inlet angle is increased, and the roll angle is reduced.

Schematic diagram of hull stability

The hull itself is in a state of dynamic balance. The design considers the stability when the ship leaves the equilibrium position and tilts under the action of external forces. The ability of the ship to tilt away from its equilibrium position and return to its original equilibrium position on its own after the external force is removed is called ship stability.

The basic principle is as shown in the figure above. When the ship is acted upon by a heeling moment Mh, it floats to one side and tilts an angle θ (θ≤100~150). The water plane moves from WL to W1L1. After tilting: < /p>

1. The force W remains unchanged because there is no increase or decrease in weight during the tilting process;

2. The position of the center of gravity G remains unchanged because there is no weight movement during the tilting process. ;

3. The size of the buoyancy force D does not change, because the weight does not change, so the displacement does not change;

4. Only the position of the center of buoyancy B changes due to the change in the shape of the drainage volume, Move from the original B to the inclined side to the inclined side of B to B1.

Due to the buoyancy of water, a righting moment Ma opposite to the heeling moment Mh will be generated to bring the ship back to the equilibrium position.

Stability is divided into lateral stability and longitudinal stability according to the tilt state; it is divided into initial stability and large tilt angle stability according to the tilt angle; static stability is divided into static stability according to the presence or absence of angular acceleration during tilt. stability and dynamic stability; according to whether the cabin is damaged, it is divided into intact stability and damaged cabin stability. The stability of the cargo ship changes greatly with the position of the center of gravity and center of buoyancy of cargo loading and unloading, and the stability also changes accordingly. Cruise ships generally have small changes in their center of gravity and center of buoyancy, and their stability is considered to be basically stable.

Hull rocking is the main cause of seasickness, and it is also the biggest test for cruise ships in terms of preventing motion sickness. At present, in addition to investing in speed, the most important thing in cruise ship hull design is to resist complex sea conditions and create a cruise ship with minimal shaking and the highest comfort. In the state of dynamic balance of the hull, increasing the ship's width, increasing the freeboard height, lowering the height of the center of gravity, reducing the wind pressure side moment arm, increasing the water inlet angle, reducing the rolling angle, etc. can all improve the hull's sea resistance. The role of sex.

Seakeeping refers to the ability of a ship to overcome motions such as swaying on waves. In order to improve the ship's seakeeping, reduce the rolling amplitude and change the rolling period, which are the key purposes of achieving ship comfort, anti-rolling equipment is usually installed on the ship:

1. Catamaran design

Many of the high-speed cruise ships you see have a catamaran design. Generally speaking, two hulls are connected, usually equipped with twin propellers and twin rudders, and have good control performance. The catamaran design greatly improves the ship's center of buoyancy and reduces the center of gravity. As mentioned above, the distance between the center of buoyancy and the center of gravity determines the stability of the ship. Therefore, the stability of this type of ship is greatly improved, and the sway is less than that of a monohull ship, which in turn increases the Overall crew comfort and reduced chance of seasickness. At the same time, there is no need to install "stabilizer" equipment, which also reduces the purchase cost.

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

2. Installation of bilge keels

Bilge keels are the most widely used The most extensive and simplest anti-rolling device. It is installed on the bilge of the ship along the length of the ship. When rolling, it disturbs the flow field around the hull, causing the ship to generate additional damping, thereby increasing the rolling damping and achieving the purpose of passive anti-rolling. The anti-rolling device is effective in any sea state, especially when the periodic swaying of the ship and the periodic action of waves produce the most significant effect. The only drawback is that installing a bilge keel will slightly increase the ship's resistance. Due to its simple structure, low construction cost and little impact on speed, bilge keels are installed on almost all seagoing ships without exception, and it has become a part of the hull of seagoing ships. Therefore, in general, the so-called anti-rolling device refers to anti-rolling measures and equipment other than the bilge keel.

Oasis of the Seas

3. Installation of fin stabilizers

The fin stabilizer device is currently the most installed anti-rolling device on ships in the world. During the swing process, the control mechanism automatically adjusts the angle of the stabilizer fin relative to the water flow, so that the left and right stabilizer fins generate the maximum moment opposite to the swing direction to achieve the effect of anti-roll. This kind of anti-rolling device has a good effect, especially for passenger ships with higher speeds. It is an active anti-rolling device with high anti-rolling effect and is widely used. The anti-rolling fin first appeared in 1889 and was patented by John I. Thomeyeroft. In 1923, Japan's Genraoshi Shintaro designed the first set of stabilizer fins, which achieved good anti-roll effects after shipment testing. In 1935, the fin stabilizer designed by the British Brown Brothers was successfully applied to a 2,200-ton Channel ferry. Since then, the fin stabilizer has been widely used. The working principle of the fin stabilizer is:

The violent swaying of the ship is a vector synthesis of six motion states: rolling, pitching, heaving, rolling, lateral drift and longitudinal drift. Among them, the roll has the greatest impact on the stable navigation of the ship. The function of the stabilizer is to reduce the sway produced when the ship sails in strong winds and waves, so as to effectively control the sailing attitude of the ship. Fin stabilizers are currently the only active anti-roll devices that are widely used. Its working part is a pair or several pairs of wing-shaped fins extending outboard. According to the retractability of the fins, it can be divided into two types: retractable type and fixed type. Rotates on its own axis while working. From the theory of fluid mechanics, it can be known that when the fin and the water flow make relative motion, a force perpendicular to the wing surface will be generated. This is the basic principle of the stabilizer fin. The reason why the fin stabilizer can play an anti-rolling role is precisely because it can obtain a stable moment in the water flow through one or several pairs of controlled rotating fins to resist the impact force of the waves and reduce the roll of the ship. , thereby improving the seaworthiness of the ship.

With the rapid development of control technology in recent years, the fin stabilizer has evolved into the most commonly used and successful anti-roll device. However, the anti-roll effect of the fin stabilizer is proportional to the square of the speed. When the ship's speed is high, the stabilizer can effectively reduce the roll. When the ship is operating at zero speed or low speed, the stabilizer cannot effectively reduce the roll.

China's State Oceanic Administration's "Haijian 51"

4. Installation of anti-rolling tanks

Compared with fin stabilizers, which require high speed to function Function, the anti-rolling water tank is not affected by the ship's speed. Its working principle is that there is a water tank connected to the left and right inside the hull. When the ship rolls, the water in the water tank also moves from one side to the other. Oscillating motion back and forth on one side; through the design of the cross-section size of the connecting pipe and the adjustment device, the water level difference on both sides is controlled, so that the weight difference of the water in the left and right water tanks generates a moment opposite to the swing direction to achieve the purpose of anti-rolling.

Anti-rolling water tanks can be divided into three types: passive, controllable passive and active according to their working methods. The passive anti-rolling water tank works according to the principle of double vibration, and has a good anti-rolling effect in the harmonic rolling area. It has the characteristics of simple structure, low cost, easy maintenance, etc., and has been widely used. The controllable passive anti-roll tank is an anti-roll device that emerged with the rapid development of control technology. It is an important improvement to the passive anti-roll tank. It takes into account the expensive fin stabilizer device and the passive anti-roll tank. The relationship between the two, the control system requires less power, has the characteristics of automation, small space, simple operation and high reliability. In addition, the controllable passive anti-roll water tank can be used to resist heeling and detect stability. It is the current anti-roll The development direction of water tanks has broad application prospects and research value. The passive anti-rolling water tank works based on the natural rolling period of the water tank itself. When the actual wave period is greatly different from the natural period of the water tank, the water tank often cannot achieve the expected anti-rolling effect. Under certain sea conditions Increased rolling may also occur. The disadvantage is that it occupies a considerable volume in the hull, and its free liquid surface always lowers the height of the ship's center of tilt, which reduces the initial rolling stability. Active anti-rolling water tank has the advantages of fast response and speed, but its cost is high, the system is complex, and it consumes high power, so it is rarely used.

Automatic balance control system (note)

5. Application of rudder anti-roll technology

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

Rudder anti-roll devices have many advantages compared with fin stabilizers and anti-roll tanks, and have received varying degrees of attention in many countries. It can utilize the existing rudder and steering system on the ship, and can be applied not only on large and medium-sized military ships, special ships and civilian ships, but also on small boats. The requirements of rudder resistance on the dynamic characteristics of the control system and the hydrodynamic characteristics of the ship are generally easy to meet, so it has extremely broad application prospects.

6. Psychological factor control

In addition to the above design of the ship's anti-rolling device, in order to ensure the comfort of tourists, there must be no noise, no vibration, and no loud noises in the guest rooms. amplitude of shaking. For this reason, some cruise ships use electric propulsion to avoid the vibration and noise of the main engine; through reasonable planning of the space scale in the cruise ship cabin, people can sit and lie down more comfortably, which can reduce the degree of seasickness; and the air-conditioning system is carefully designed , ensuring that there is no air-conditioning noise in the room and ensuring that fresh air is supplied to every corner of the ship; measures such as psychologically soothing passengers through the coordinated design of cabin colors can alleviate the factors that cause seasickness in the human body to a certain extent.

Cruise ships will be the main means of transportation for sea passengers in the future, and people’s demand for the comfort of luxury cruise ships is becoming stronger and stronger. Therefore, in terms of cruise ship design, how to use modern technology to transform cruise ships into Reduce seasickness factors by yourself.

Note: Xu Jingjing and Tan Yue, "Research on Automatic Control Design Scheme of Ship Balance Control System", "China Ship Repair" Issue 3, 2005