Influence of relations on the stability of the ship. Elements of initial transverse stability

The stability of a vessel is its property, due to which the vessel, when exposed to external factors (wind, waves, etc.) and internal processes (displacement of cargo, movement of liquid reserves, the presence of free liquid surfaces in compartments, etc.) does not roll over. The most capacious definition of ship stability can be the following: the ability of a ship not to capsize when exposed to natural marine factors (wind, waves, icing) in the navigation area assigned to it, as well as in combination with “internal” reasons caused by the actions of the crew

This feature is based on the natural property of an object floating on the surface of the water - it tends to return to its original position after the termination of this impact. Thus, stability, on the one hand, is natural, and, on the other hand, requires regulated control by the person involved in its design and operation.

Stability depends on the shape of the hull and the position of the vessel's CG, therefore, by choosing the right hull shape in the design and proper placement of cargo on the vessel during operation, it is possible to ensure sufficient stability to ensure that the vessel does not capsize under any sailing conditions.

Vessel inclinations are possible for various reasons: from the action of incoming waves, due to asymmetric flooding of compartments during a hole, from the movement of goods, wind pressure, due to the acceptance or expenditure of goods, etc. There are two types of stability: transverse and longitudinal. From the point of view of navigation safety (especially in stormy weather), the most dangerous are transverse inclinations. Lateral stability manifests itself when the vessel rolls, i.e. when tilting it on board. If the forces that cause the vessel to tilt act slowly, then the stability is called static, and if it is fast, then dynamic. The inclination of the vessel in the transverse plane is called roll, and in the longitudinal plane - trim; the angles formed in this case are denoted respectively by O and y. Stability at small angles of inclination (10 - 12 °) is called initial stability.

(fig.2)

Imagine that under the action of external forces, the ship received a roll at an angle of 9 (Fig. 2). As a result, the volume of the underwater part of the vessel retained its value, but changed its shape; on the starboard side, an additional volume entered the water, and on the port side, an equal volume came out of the water. The center of magnitude has moved from the initial position C towards the roll of the vessel, to the center of gravity of the new volume - point C1. When the vessel is inclined, the gravity P applied at point G and the support force D applied at point C, remaining perpendicular to the new waterline V1L1, form a pair of forces with a shoulder GK, which is a perpendicular lowered from point G to the direction of the support forces.

If we continue the direction of the support force from point C1 to the intersection with its original direction from point C, then at small angles of heel, corresponding to the conditions of initial stability, these two directions will intersect at point M, called the transverse metacenter.

The mutual position of points M and G allows you to establish the following sign characterizing the lateral stability: (Fig. 3)

A) If the metacenter is located above the center of gravity, then the restoring moment is positive and tends to return the ship to its original position, i.e., when heeling, the ship will be stable.
B) If point M is below point G, then with a negative value of h0, the moment is negative and will tend to increase the roll, i.e., in this case, the vessel is unstable.
C) When the points M and G coincide, the forces P and D act along one vertical line, no pair of forces arise, and the restoring moment is zero: then the ship must be considered unstable, since it does not tend to return to its original equilibrium position (Fig. 3 ).

Fig.3

External signs of negative initial stability of the ship are:

-- sailing of the ship with a roll in the absence of heeling moments;
- the desire of the ship to roll over to the opposite side when straightening;
- transfer from side to side during circulation, while the roll remains even when the ship enters a direct course;
-- a large amount of water in the holds, on platforms and decks.

Stability, which manifests itself with the longitudinal inclinations of the vessel, i.e. when trimmed, is called longitudinal.

With the longitudinal inclination of the vessel at an angle w around the transverse axis Ts.V. will move from point C to point C1 and the support force, the direction of which is normal to the current waterline, will act at an angle w to the original direction. The lines of action of the original and new direction of the support forces intersect at a point. The point of intersection, the line of action of the forces of support at an infinitely small inclination in the longitudinal plane is called the longitudinal metacenter M. seaworthy stability propulsion ship

The longitudinal moment of inertia of the waterline area IF is much greater than the transverse moment of inertia IX. Therefore, the longitudinal metacentric radius R is always much larger than the transverse r. It is tentatively considered that the longitudinal metacentric radius R is approximately equal to the length of the vessel. Since the value of the longitudinal metacentric radius R is many times greater than the transverse r, the longitudinal metacentric height H of any ship is many times greater than the transverse one h. therefore, if the ship has transverse stability, then longitudinal stability is certainly ensured.

Factors affecting ship stability that have a strong influence on ship stability.

Factors to be taken into account when operating a small boat include:

1. The stability of the vessel is most significantly affected by its width: the greater it is in relation to its length, height and draft, the higher the stability. A wider vessel has more righting moment.
2. The stability of a small vessel increases if the shape of the submerged part of the hull is changed at large angles of heel. On this statement, for example, the action of side bollards and foam fenders is based, which, when immersed in water, create an additional restoring moment.
3. Stability deteriorates if there are fuel tanks on the ship with a surface mirror from side to side, so these tanks must have partitions installed parallel to the center plane of the ship, or be narrowed in their upper part.
4. Stability is most strongly affected by the placement of passengers and cargo on the ship, they should be placed as low as possible. It is impossible to allow people on board and their arbitrary movement to sit on a small vessel during its movement. Loads must be securely fastened to prevent their unexpected displacement from their regular places.
5. In case of strong wind and waves, the action of the heeling moment (especially dynamic) is very dangerous for the vessel, therefore, with the deterioration of weather conditions, it is necessary to take the vessel to shelter and wait out the bad weather. If this is not possible due to the considerable distance to the shore, then in stormy conditions you should try to keep the ship "bow to the wind", throwing out the floating anchor and running the engine at low speed.

Excessive stability causes rapid pitching and increases the risk of resonance. Therefore, the register set limits not only for the lower, but also for the upper limit of stability.

To increase the stability of the vessel (increase in the restoring moment per unit of heel angle), it is necessary to increase the metacentric height h by appropriate placement of cargo and stores on the ship (heavier cargo at the bottom, and lighter cargo at the top). For the same purpose (especially when sailing in ballast - without cargo), they resort to filling ballast tanks with water.

Stability is the ability of a vessel deviated from the equilibrium position to return to it after the cessation of the forces that caused the deviation.

Vessel inclinations can occur from the action of oncoming waves, due to asymmetric flooding of compartments during a hole, from the movement of goods, wind pressure, due to the acceptance or expenditure of goods.

The inclination of the ship in the transverse plane is called roll, and in the longitudinal trim. The angles formed in this case are denoted respectively by θ and ψ

The stability that a ship has in longitudinal inclinations is called longitudinal. It is, as a rule, quite large, and the danger of capsizing the vessel through the bow or stern never arises.

The stability of the vessel with transverse inclinations is called transverse. It is the most important characteristic of the ship, which determines its seaworthiness.

There are initial transverse stability at small angles of heel (up to 10 - 15 °) and stability at large inclinations, since the restoring moment at small and large angles of heel is determined in various ways.

initial stability. If the vessel is under the influence of an external heeling moment M KR(for example, wind pressure) will roll by an angle θ (the angle between the original WL 0 and current WL 1 waterlines), then, due to a change in the shape of the underwater part of the vessel, the center of magnitude WITH move to a point From 1(Fig. 5). Sustaining power yV will be applied at the point C1 and directed perpendicular to the current waterline WL 1 . Dot M located at the intersection of the diametrical plane with the line of action of the supporting forces and is called transverse metacenter. Vessel weight force R stays in the center of gravity G. Together with strength yV it forms a pair of forces that prevents the vessel from tilting by the heeling moment M KR. The moment of this pair of forces is called restoring moment M V. Its value depends on the shoulder l=GK between the forces of weight and support of an inclined vessel: M B \u003d Pl \u003d Ph sin θ, Where h- point elevation M above the ship's CG g, called transverse metacentric height ship.

Rice. 5. The action of forces during the roll of the ship.

It can be seen from the formula that the value of the restoring moment is the greater, the greater h. Therefore, the metacentric height can serve as a measure of stability for a given vessel.

Value h of a given ship at a certain draft depends on the position of the center of gravity of the ship. If the loads are placed so that the ship's center of gravity takes a higher position, then the metacentric height will decrease, and with it the static stability arm and the restoring moment, i.e., the ship's stability will decrease. With a decrease in the position of the center of gravity, the metacentric height will increase, the stability of the vessel will increase.

Since for small angles their sines are approximately equal to the angles measured in radians, we can write M B = Phθ.

The metacentric height can be determined from the expression h = r + zc - z g , Where z c- elevation of the CV over the OL; r- transverse metacentric radius, i.e., the elevation of the metacenter above the CV; z g- elevation of the ship's CG above the main one.

On a built ship, the initial metacentric height is determined empirically - inclining, i.e., the transverse inclination of the vessel by moving a load of a certain weight, called roll-ballast.

Stability at high angles of heel. As the ship's roll increases, the restoring moment first increases, then decreases, becomes equal to zero, and then not only does not prevent the inclination, but, on the contrary, contributes to it (Fig. 6).

Rice. 6. Diagram of static stability.

Since the displacement for a given load state is constant, the restoring moment changes only due to a change in the lateral stability arm l st. According to the calculations of transverse stability at large angles of heel, static stability chart, which is a graph expressing the dependence l st from the roll angle. The static stability diagram is built for the most typical and dangerous cases of ship loading.

Using the diagram, it is possible to determine the heeling angle from a known heeling moment or, conversely, to find the heeling moment from a known heeling angle. The initial metacentric height can be determined from the static stability diagram. To do this, a radian equal to 57.3 ° is laid off from the origin of coordinates, and the perpendicular is restored to the intersection with the tangent to the curve of the stability shoulders at the origin. The segment between the horizontal axis and the intersection point on the scale of the diagram will be equal to the initial metacentric height.

With a slow (static) action of the heeling moment, the state of equilibrium during a roll occurs if the condition of equality of the moments is observed, i.e. M KR \u003d M B(Fig. 7).

Rice. 7. Determination of the roll angle from the action of statically (a) and dynamically (b) applied force.

With the dynamic action of the heeling moment (a gust of wind, a jerk of the towing cable on board), the vessel, tilting, acquires an angular velocity. By inertia, it will pass the position of static equilibrium and will continue to heel until the work of the heeling moment becomes equal to the work of the restoring moment.

The value of the angle of heel under the dynamic action of the heeling moment can be determined from the static stability diagram. The horizontal line of the heeling moment is continued to the right until the area ODSE(work of the heeling moment) will not become equal to the area of the figure BOTH(restoring moment work). At the same time, the area OASE is common, so we can restrict ourselves to comparing areas OH YEAH And ABC.

If the area bounded by the restoring moment curve is insufficient, the ship will capsize.

The stability of seagoing vessels must meet the Register requirements, according to which it is necessary to fulfill the condition (the so-called weather criterion): K \u003d M def min / M d max ≥ 1" where M def min- minimum overturning moment (minimum dynamically applied heeling moment, taking into account pitching), under the influence of which the vessel will not lose stability yet; M d max- dynamically applied heeling moment from wind pressure at the worst loading option in terms of stability.

In accordance with the requirements of the Register, the maximum arm of the static stability diagram lmax shall be not less than 0.25 m for vessels of 85 m in length and not less than 0.20 m for vessels over 105 m at an angle of heel θ of more than 30°. The slope angle of the diagram (the angle at which the curve of the stability arms intersects the horizontal axis) for all vessels must be at least 60°.

Influence of liquid cargoes on stability. If the tank is not filled to the top, that is, it has a free liquid surface, then when tilted, the liquid will overflow in the direction of the roll and the center of gravity of the vessel will shift to the same side. This will lead to a decrease in the stability arm and, consequently, to a decrease in the restoring moment. At the same time, the wider the tank, in which there is a free surface of the liquid, the more significant will be the decrease in lateral stability. To reduce the influence of the free surface, it is advisable to reduce the width of the tanks and strive to ensure that during operation there is a minimum number of tanks with a free surface of the liquid.

Influence of bulk cargoes on stability. When transporting bulk cargo (grain), a slightly different picture is observed. At the beginning of the inclination, the load does not move. Only when the angle of heel exceeds the angle of repose does the cargo begin to spill. In this case, the spilled cargo will not return to its previous position, but, remaining at the side, will create a residual roll, which, with repeated heeling moments (for example, squalls), can lead to loss of stability and capsizing of the vessel.

To prevent spillage of grain in the holds, suspended longitudinal semi-bulkheads are installed - shifting boards or stack sacks of grain on top of the grain poured in the hold (cargo bagging).

Effect of a suspended load on stability. If the cargo is in the hold, then when it is lifted, for example, by a crane, there is, as it were, an instantaneous transfer of the cargo to the suspension point. As a result, the ship's CG will shift vertically upward, which will lead to a decrease in the righting moment arm when the ship receives a roll, i.e., to a decrease in stability. In this case, the decrease in stability will be the greater, the greater the mass of the load and the height of its suspension.

The vessel's longitudinal stability is much higher than its transverse stability, therefore, for the safety of navigation, it is most important to ensure proper transverse stability.

Depending on the magnitude of the inclination, stability is distinguished at small angles of inclination ( initial stability) and stability at large angles of inclination.

Depending on the nature of the acting forces, static and dynamic stability are distinguished.

Static stability- is considered under the action of static forces, that is, the applied force does not change in magnitude. Dynamic stability- is considered under the action of changing (i.e. dynamic) forces, for example, wind, sea waves, cargo movement, etc.

Initial lateral stability

Initial transverse stability. The system of forces acting on the ship

With a roll, stability is considered as initial at angles up to 10-15 °. Within these limits, the restoring force is proportional to the angle of heel and can be determined using simple linear relationships.

In this case, the assumption is made that deviations from the equilibrium position are caused by external forces that do not change either the weight of the vessel or the position of its center of gravity (CG). Then the immersed volume does not change in magnitude, but changes in shape. Equal-volume inclinations correspond to equal-volume waterlines, cutting off equal immersed hull volumes. The line of intersection of the planes of the waterlines is called the axis of inclination, which, with equal volume inclinations, passes through the center of gravity of the waterline area. With transverse inclinations, it lies in the diametrical plane.

Free surfaces

All the cases discussed above assume that the center of gravity of the ship is stationary, that is, there are no loads that move when tilted. But when such weights are present, their influence on stability is much greater than the others.

A typical case is liquid cargoes (fuel, oil, ballast and boiler water) in partially filled tanks, that is, with free surfaces. Such loads are capable of overflowing when tilted. If the liquid cargo fills the tank completely, it is equivalent to a solid fixed cargo.

Influence of free surface on stability

If the liquid does not fill the tank completely, i.e. has a free surface, which always occupies a horizontal position, then when the ship is tilted at an angle θ the liquid overflows in the direction of inclination. The free surface will take the same angle relative to the design line.

Levels of liquid cargo cut off equal volumes of tanks, i.e. they are like waterlines of equal volume. Therefore, the moment caused by the transfusion of liquid cargo when heeling δm θ, can be represented similarly to the moment of shape stability m f, only δm θ opposite m f by sign:

δm θ = - γ f i x θ,

Where i x- the moment of inertia of the area of the free surface of the liquid cargo relative to the longitudinal axis passing through the center of gravity of this area, γ- specific gravity of the liquid cargo

Then the restoring moment in the presence of a liquid load with a free surface:

m θ1 = m θ + δm θ = Phθ − γ x i x θ = P(h − γ x i x /γV)θ = Ph 1 θ,

Where h- transverse metacentric height in the absence of transfusion, h 1 = h − γ g i x /γV- actual transverse metacentric height.

The influence of the overflowing load gives a correction to the transverse metacentric height δ h \u003d - γ w i x / γV

The densities of water and liquid cargo are relatively stable, that is, the main influence on the correction is the shape of the free surface, or rather its moment of inertia. This means that the lateral stability is mainly affected by the width, and the longitudinal length of the free surface.

The physical meaning of the negative value of the correction is that the presence of free surfaces is always reduces stability. Therefore, organizational and constructive measures are being taken to reduce them:

When a heeling moment is applied to the ship m cr, constant in magnitude, it receives a positive acceleration with which it begins to roll. As the inclination increases, the restoring moment increases, but at the beginning, up to the angle θ st, at which m cr = m θ, it will be less heeling. Upon reaching the angle of static equilibrium θ st, the kinetic energy of rotational motion will be maximum. Therefore, the ship will not remain in the equilibrium position, but due to the kinetic energy it will roll further, but slower, since the restoring moment is greater than the heeling moment. The previously accumulated kinetic energy is repaid by the excess work of the restoring moment. As soon as the magnitude of this work is sufficient to completely extinguish the kinetic energy, the angular velocity will become equal to zero and the ship will stop heeling.

The largest angle of inclination that the ship receives from the dynamic moment is called the dynamic angle of heel. θ dyn. In contrast to it, the angle of heel with which the ship will sail under the action of the same moment (according to the condition m cr = m θ), is called the static bank angle θ st.

Referring to the static stability diagram, work is expressed as the area under the restoring moment curve m in. Accordingly, the dynamic bank angle θ dyn can be determined from the equality of areas OAB And BCD corresponding to the excess work of the restoring moment. Analytically, the same work is calculated as:

on the interval from 0 to θ dyn.

Reaching dynamic bank angle θ dyn, the ship does not come into equilibrium, but under the influence of an excess restoring moment, it begins to straighten rapidly. In the absence of water resistance, the ship would enter into undamped oscillations around the equilibrium position when heeling θ st Marine Dictionary - Refrigerated vessel Ivory Tirupati initial stability is negative Stability the ability of a floating facility to withstand external forces that cause it to roll or trim and return to a state of equilibrium at the end of the perturbing ... ... Wikipedia

A vessel whose hull, when moving, rises above the water under the action of the lifting force created by the wings submerged in the water. A patent for S. on a p. to. was issued in Russia in 1891, however, these ships began to be used from the 2nd half of the 20th century ... ... Great Soviet Encyclopedia

A cross-country vehicle capable of moving both on land and on water. The amphibious car has an increased volume of a sealed body, which is sometimes supplemented with mounted floats for better buoyancy. Movement on water ... ... Encyclopedia of technology

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“...Be careful! squeaked the one-eyed captain. But it was already too late. Too many fans have accumulated on the starboard side of Vasyukin's dreadnought. Having changed the center of gravity, the barge did not oscillate and turned over in full accordance with the laws of physics.

This episode from classical literature can be used as an illustrative example loss of stability from moving the center of gravity due to the accumulation of passengers on one side. Not always, unfortunately, the matter is limited to funny swimming: the loss of stability often leads to the death of the ship, and often people, sometimes several hundred people at the same time (recall the recent tragedy - the death of the ship "Bulgaria" ... - ed. .).

In the history of world shipbuilding, a number of cases are recorded, similar to what happened at the beginning of the century with the American multi-deck river steamer General Slocum. Its designers provided everything for the convenience of passengers, but did not check how the ship would behave if all 700 of its inhabitants at once went up to the upper promenade deck and at the same time approached the board to admire the view...

Loss of stability is one of the most common causes of small craft accidents. That is why each of the captains, regardless of how his ship looks like - a kayak or, say, a displacement boat, each of those who rest on the water must have an idea of the "laws of physics", ignorance of which cost Vasyukin dearly. In other words, about the seaworthiness of a vessel, which shipbuilders call stability.

Stability- this is the ability of the vessel to resist the heeling action of external forces and return to a straight position after the termination of this action. This term appeared in our country in the 18th century, when Russia became a maritime power; in origin and meaning, it is a variation of the common word "sustainability".

We are constantly confronted with the stability of balance in everyday life. It's no secret to us that a chair is easier to tip over than a sofa; and an empty bookcase is lighter than one filled with books. Turning a heavy box over the rib, we first apply the greatest effort, then it becomes easier for us, and finally, when the imaginary line drawn vertically through the center of gravity of the box passes over the rib, the box turns over by itself, without our participation. Having made sure that a low wide box is more difficult to turn over than a tall and narrow one, and a heavy one is more difficult than a light one, we can come to the conclusion that the stability of the body on a hard surface is determined by its weight and the horizontal distance from the center of gravity to the edge of the supporting plane - the shoulder lever . The more weight and shoulder, the more stable the body.

This simple law is also valid for a floating ship, but here the matter is complicated by the fact that instead of a solid surface, water serves as a support for the “overturning” ship. In principle, as in the case just described, the stability of the vessel is determined by its weight and shoulder - the mutual arrangement of the points of application of two forces.

One of them is the weight, i.e. gravity, applied at the center of gravity of the ship (CG) and always directed vertically down.

The other is the buoyancy force or sustaining force. According to the law of Archimedes for a floating vessel, this force is equal in magnitude to gravity, but is directed vertically upwards. The point of application of the resultant forces of support is the fulcrum of the ship! This point is located in the center of the volume of the hull submerged in water and is called the center of buoyancy or center of magnitude(CV).

When the ship floats freely in a straight position, the CV is always on the same vertical with the CG, and the equal and opposite forces acting on the ship are balanced. But now heeling forces began to act on the ship. This is not necessarily the movement of passengers; it can be a gust of wind or, if we are talking about a yacht, just its pressure on the sails, a steep wave, a jerk of a towline, centrifugal force in a steep circulation, a bather rising from the water over the side, etc., etc.

The action of the moment of this heeling force, i.e. heeling moment, tilts - rolls the ship. At the same time, the CG of the vessel does not change the position, unless, of course, this is the same "Vasyukin" case and there are no such loads on the vessel that can move in the direction of the slope. Since the ship continues to float even when heeling, that is, the law of Archimedes continues to operate, an increase in the immersed volume on the side of the side entering the water corresponds to an equal decrease in the immersed volume on the opposite side leaving the water. Let's not forget: the weight of the vessel does not change from the action of the heeling moment; therefore, the total value of the immersed volume must remain unchanged!

Due to this redistribution of the underwater volume, the position of the CV changes - it moves away towards the ship's heeling; as a result, a moment of support forces arises, tending to restore the direct position of the ship and therefore called restoring moment.

While the vessel maintains stability, the restoring moment, increasing as the roll increases, becomes equal to the heeling moment and, since it is directed in the opposite direction, completely “paralyzes” its action. This means that if the magnitude of the heeling forces does not change anymore, the ship will continue to float with a constant list; if the action of the heeling forces ceases and there is no heeling moment, the restoring moment will immediately straighten the ship.

Turning to scheme 2, we can assume that the value of the restoring moment arising during a roll will be the greater, the greater the shoulder - the horizontal distance between the new position of the CV and the unchanged position of the CV; that's why it's called stability shoulder. As long as this shoulder is present, the restoring moment is in effect - the ship retains , but as soon as the shoulder disappears with a further increase in the roll, the CV will be on the same vertical with the CG, no further efforts will be required to capsize the ship, it will lose stability - it will capsize.

The farther the center of magnitude can go in the direction of inclination - the greater the stability shoulder, the more difficult it is to turn the vessel over, that is, the more stable it is. That is why a wide vessel will always be noticeably more stable than a narrow one. On a four-oared yal, which has a width of 1.6 m, rowers can get up and walk without much risk, but on an academic eight with a width of 0.7 m, it is enough for one rower to rest his foot more strongly or raise the oar a little higher to cause a threatening roll!

It is especially important to have sufficient width on the smallest boats. Significantly affects their stability and the completeness of the waterline, i.e., an indicator of what proportion of the rectangle, the sides of which are made up of maximum length and width, occupies the area of \u200b\u200bthe current waterline. Other things being equal, vessels with greater waterline fullness are always more stable than those with sharp waterlines in the bow and stern.

Stability, especially at low angles of inclination, largely depends on the shape of the hull - on the distribution of volumes of the underwater part of the hull. After all, in the end, stability is determined not just by the width of the current waterline, but by the position of the “fulcrum” - the center of the actually submerged volume.

From the point of view of stability, the least advantageous are semicircular sections, which, according to the conditions of propulsion, are often used for displacement ships; close to semicircular sections have hulls of rowing academic boats, as well as relatively narrow and long boats not designed for gliding. Rectangular section has higher characteristics of initial stability; this kind of section is made on boats of minimum length - tuziks and punt shuttles. If, however, the underwater volumes are extended to the sides due to a decrease in draft (and volume) in the middle part, stability will benefit even more: the hulls of such newest universal small boats as, for example, Sportiak and Dolphin, have a similar shape.

Following the same path, you can further increase the stability by cutting the hull lengthwise - along the DP - and placing the narrow halves at some width. This is how we approached the idea of a double-hull vessel, which is embodied in the designs of both low-speed floating cottages or inflatable rafts, and racing motor or sailing catamarans designed for record speeds.

With an increase in the angles of inclination, the shape of the surface part of the hull in the area entering the water when heeling becomes more and more important. A good example is the lack of stability of a log with a circular cross section: with any of its "roll" - rotation around the axis - no additional volume enters the water, the shape of the immersed part and the position of the CV do not change, there is no restoring moment.

For the same reason, the once-fashionable obstruction of the sides on motorboats is also harmful. It is understandable: with an increase in the roll, the width of the waterline not only does not increase, but sometimes vice versa - it decreases! Therefore, at sharp turns, the old Kazankas often turned over, which had a blockage of the sides inward in the already rather narrow aft.

And vice versa: measures that increase stability are the collapse of the sides and the fastening of additional buoyancy elements along their upper edges. The explanation is simple: when heeling, volumes enter the water exactly where they are most needed for support - where they give a large leverage. In principle, a ship with a flare on the surface and with a relatively narrow running waterline combines good speed with high stability. For example, ancient galleys had such a hull shape, where, as you know, the power of the “engine” was limited, and the requirements for speed and seaworthiness were quite high. For the same purpose, bundles of dry reeds were tied over the sides of light Cossack "gulls".

In fact, our tourists-sailboats use the same technique, attaching inflatable balloons to the sides of the kayaks. An even more effective means of increasing the stability of kayaks when sailing are side floats mounted on crossbars. On an even keel, they go above the water and do not slow down the movement. When the wind pressure on the sail tilts the trimaran kayak, the leeward float enters the water and serves as an additional support located very favorably - far from the DP.

Various side attachments on gliding motor boats serve a similar purpose - boules and sponsons: they improve the stability of the boat or motorboat both in the parking lot and on the move. The same "Kazanka" becomes safer even when operating with the "Whirlwind" due to the installation of additional buoyancy volumes - stern boules entering the water when the stern is obviously overloaded or when heeling in the parking lot. When moving straight ahead, the lower working surface of the boules is above the running waterline, and with sharp turns dangerous for the Kazanka, this surface begins to “work”: the hydrodynamic lifting force formed on it during gliding prevents an increase in roll on circulation.

Effective waterline length, although to a lesser extent than the width, also significantly affects the stability of the smallest vessels. Here is an illustrative case. Once a sectional tourist kayak was tested. In a single three-section version, the boat turned out to be too “sporty”: those who had no experience in rowing “academic girls” invariably capsized near the shore. However, it was enough to add another middle section 0.8 m long, as the same boat became a "calm" tourist vessel.

Stability is very closely related to another seaworthy quality of the vessel - unsinkability. We emphasize that both of these qualities and to a large extent determine the actual freeboard. If the freeboard is low, then already at small angles of heel the deck will enter the water, the width of the effective waterline will begin to decrease, and from that moment the stability arm and the restoring moment will begin to fall. Open - deckless boats, after entering the water of the upper edge of the side, immediately fill up and capsize (this is how the Vasyukinites, who were not experienced in the theory of the ship, suffered!). It is clear that the higher the freeboard, the greater the allowable heel angle, the critical value of which is called the flood angle.

The most obvious indicator of a dangerous increase in the list and approaching the angle of flooding is a decrease in the surface height on the side of the roll of the boat. Needless to say, the smaller the boat, the more dangerous any roll, the more important every centimeter of the actual freeboard! It is absolutely unacceptable to exceed the load capacity of the boat specified by the manufacturer (overloading)! It is dangerous to place the loads in such a way that the boat is heeling already at the moment of leaving the shore: after all, this immediately reduces the actual height of the side and the stability margin of your boat!

It is no coincidence that we are talking about the actual height of the freeboard. The history of "big" shipbuilding knows many cases when whole and unharmed ships lost their stability only due to the fact that when heeling near the surface of the water, some open holes in the side accidentally turned out to be.

Academician A.P. Krylov tells a curious story. Before the 84-gun ship King George went on its maiden voyage (this happened in 1782 in Portsmouth), it was specially heeled to correct some kind of malfunction of the kingstons. The edges of the lower row of open gun ports were at the same time only 5-8 cm above the water surface. The senior officer, not realizing the dangerous position of the ship, when it was these 5-8 cm, and not the usual 8 m, that was the actual height of the side, ordered the team to be called to the guns to raise the flag. Obviously, the sailors were running along the heeled side, and a slight increase in the list was enough for the ship to board and carry more than 800 people to the bottom ...

So, the necessary conditions for the stability of the vessel are its sufficient width and height of the side. Let's make a clarification now. The fact is that stability is usually divided into initial (within the angle of heel up to 10-20 °) and stability at high inclinations. For small vessels, first of all, the width and characteristics of the initial stability are important: stability at large angles of heel most often “does not reach”, since the flood angle usually lies within the initial stability. For larger seaworthy and closed - decked vessels, the freeboard height is more important, providing stability at high inclinations.

Now we note one more completely obvious and practically very important condition: the more stable the ship, the lower its center of gravity is. Everyone knows what they owe their high “stability” to roly-poly and roly-poly! From our own experience, everyone is well aware of how any small boat begins to sway when they stand up in it to their full height and try to go from one bank to another: with an increase in the height of the CG (shoulder), the heeling moment increases significantly, although the person’s weight itself does not change ...

That is why on the same kayaks, the width of which, as a rule, is at a dangerous minimum limit, you have to sit almost directly on the bottom. Another example. When a mast is put on a yawl, a force of wind pressure on the sails applied at a certain height appears; in order to compensate for the significant heeling moment that arises, it is necessary to increase the stability in the same way - the whole team changes from the cans to the bottom.

And the third example. The editors of the collection got acquainted with a rather narrow two-seater boat (see photo), designed for rowing with long swing oars. The driving performance of the boat turned out to be excellent, but there was one “but”: while the author of the project was driving the boat to the test site, he had already turned over! The editors who tried the boat also found themselves in the water. However, it was enough to lower the height of the cans by 150 mm - the situation has changed.

Despite the most stringent weight saving regime, those vessels with especially stringent stability requirements have to take “dead weight” - ballast specifically to lower the central heating. Typically, cruising yachts and lifeboats carry permanent solid ballast, anchored as low as the ship's design allows. (The lower you can place the ballast, the less it will be needed to provide a certain height of the CG of the entire ship!) On such ships, they try to place the CG under the CG. Then the maximum value of the stability lever will be achieved with a very large roll - up to 90 ". For comparison, suffice it to say that most conventional sea boats capsize already at a roll of 60-75 °.

Sometimes they take temporary liquid ballast. So, on seaworthy motor boats and boats with keeled bottom contours, low initial stability in the parking lot (roll) often has to be compensated for by taking water into special ballast tanks in the bottom part, which are automatically emptied during movement.

It is very important that the CG of a heeled vessel remains in place: it is no coincidence that on sailboats all heavy objects are securely fastened to prevent them from moving. There are, however, goods that are considered dangerous because they can cause loss of stability. These are all kinds of bulk cargo - from grain and salt to fresh fish, randomly spilling in the direction of the ship's tilt. (It was from the displacement of bulk cargo - grain - during a hurricane that the huge four-masted barque Pamir, the last large cargo sailboat with a deadweight of 4500 tons, capsized and died in 1957!) Liquid cargo is of particular danger. We will not go into the depths of the theory of the ship, but we emphasize that in this case, it is not so much the weight of the overflowing liquid cargo that reduces stability, but exactly its free surface area.

How, the reader will ask, then tankers carrying this dangerous liquid cargo float across the seas and oceans? Firstly, the hull of the tanker is divided by transverse and longitudinal impermeable bulkheads into separate compartments - tanks, and in their upper part they put the so-called fender bulkheads, which additionally "break" the free surface (breaking it into 2 parts reduces the harmful effect on stability by 4 times). Secondly, the tanks are completely flooded.

For the same reasons, on a boat it is better to have two narrower fuel tanks than one wide one. All reserve tanks before a storm passage must be filled entirely (as the sailors say, they must be pressed in). It is necessary to spend liquids in turn - first to the end from one tank, then from the next, so that the level is free in only one of them.

The terrible enemy of small vessels is the water in the hold, even if its total weight is small. Once a new working boat came out for testing. At the very first turn, it was noted that during the circulation the boat gets an unusually large roll and very "reluctantly" leaves it. We opened the aft hatch - and saw that water was walking in the afterpeak, which got there through a barely noticeable crack in the seam.

It is very important to drain the hulls of small vessels in a timely manner, to take measures to ensure that in fresh weather water does not get inside through various holes and leaks.

With danger from disorganized passengers, we started this conversation about stability. Now that we are armed with some basic theory, we emphasize once again the need to strictly observe the established rules of conduct on board any small craft. After all, by mistake, a passenger boarding a light motorboat is a huge heeling force, which is almost 1/5 of the ship's displacement! And two passengers who decided to simultaneously pass on board Progress-4 with a wheelhouse are a real threat to capsize the ship (two such cases with a tragic outcome occurred in Kalinin last summer).

When inviting guests to your "cruiser", politely but decisively instruct them, familiarize them with the existing safety rules. On the smallest ships, it is sometimes impossible to stand up to your full height and move from place to place, and people may not know this!

Until now, it has been said that the position of the DH should not change. There is, however, a numerous class of sports vessels for which the all-round movement of the CG in the direction opposite to the roll is the most important condition for achieving high results. We are talking about the tilting of light racing dinghies and catamarans, and sometimes cruising and racing yachts. Hanging overboard with the help of a trapezoid, the athlete pushes the CG with his weight and increases the stability arm, which makes it possible to reduce the roll, and even avoid capsizing ...

Finally, it should be borne in mind that even a ship that is stable in some conditions may not be stable enough in others. Stability may differ, in particular when stationary and while driving. Therefore, one also has to take into account driving stability. For example, a displacement boat, which in the parking lot does not even react to a passenger sitting at the side, when sailing on the waves, suddenly begins to roll in his direction. It turns out that the boat, as it were, “hangs”, resting its stern and bow on the crests of two adjacent waves, and due to the fact that its entire middle part, the widest, is in the wave cavity, the fullness of the waterline already known to us has decreased and stability has immediately decreased .

On planing motorboats, the significant hydrodynamic forces that arise during movement to maintain stability, as a rule, increase. However, they can also cause capsizing: for example, when turning too sharply, a change in the direction of the propeller stop and a sharp increase (due to drift) in pressure at the outer cheekbone to turn create a dangerous pair of forces, which often turns the boat over the outer side to turn.

Finally, shipbuilders separately analyze cases of dynamic application of heeling forces (there is also a special concept - dynamic stability): with a sudden and short-term application of large external loads, the behavior of the vessel may be completely different from the classical static stability schemes. That is why, in stormy conditions, with the adverse dynamic effects of squall and wave impact, seemingly absolutely stable yachts are overturned, specially designed for sailing in the most severe ocean conditions. (The yachts of Chichester, Baranovsky, Lewis and other lone daredevils turned over! Here the subtlety is that the shipbuilders foresaw this too: the yachts immediately got up on an even keel and again became stable.)

Of course, engineers are not satisfied with assessments such as “this ship is stable, and that is not very”; shipbuilders characterize stability with exact values, which will be discussed in the next article.

When designing any ship, be it a supertanker or a rowboat, the designers make special stability calculations, and when the ship is tested, the compliance of the actual stability with the design is checked first. In order to have a guarantee that the stability of any new ship during its normal competent operation in the conditions for which it is designed is sufficient, observing organizations such as the USSR Register issue specially Stability standards and then monitor their compliance. Designers who create a ship project perform all calculations, guided by these stability standards, check whether the future ship will capsize under the influence of waves and wind. Naturally, additional requirements are imposed on certain types of vessels. So, passenger ships are now checked for cases of accumulation of all passengers on one side, and even when heeling for circulation (in this case, the angle of heel should not exceed the angle at which the deck enters the water and the value of 12 °). Towboats are checked for the action of a jerk of the towline, and river tugs for the static effect of the towline.

The results of the calculations, together with the instruction to the captain of the vessel, are recorded in one of the most important ship's documents, called "Information on the stability of the vessel."

For small boats, the River Register also recognizes full-scale trials of the lead ship carried out according to a special program. These tests may, in doubtful cases, replace the corresponding calculations.

The small pleasure fleet, controlled by navigational and technical inspections, does not yet have sufficiently clear and simple stability standards. The seaworthiness of such vessels is mainly standardized by establishing a minimum freeboard and a length-to-width ratio (from 2.3 to 1). Depending on the height of the freeboard, NTI (now GIMS) divides small vessels into three classes: the first - with a freeboard of at least 250 mm; the second - not less than 350 mm; the third - at least 500 mm.

The instructions supplied with commercial small boats usually contain basic recommendations for maintaining stability. Each amateur navigator is introduced to the safety rules before issuing him a certificate for the right to steer the vessel.

E. A. Morozov, "KiYa", 1978

There are concepts of stability of the following types: static and dynamic, with small inclinations of the vessel and with large inclinations.

Static stability - the stability of the vessel with a gradual, smooth inclination of the vessel, when the forces of inertia and water resistance can be neglected.

The laws of initial stability retain their validity only up to a certain angle of heel. The value of this angle depends on the type of vessel and the state of its loading. For ships with low initial stability (passenger and timber carriers), the maximum heel angle is 10-12 degrees, for tankers and dry cargo ships up to 25-30 degrees. The location of the CG (center of gravity) and CG (center of magnitude) are the main factors affecting the stability when the ship rolls.

Basic elements of stability: displacement ∆ , shoulder of the restoring moment (shoulder of static stability) - lct, initial metacentric radius - r,

transverse metacentric height - h, roll angle - Ơ, restoring moment - MV

Heeling moment - Mkr, stability coefficient -K, elevation of the center of gravity Zg,

center of magnitude elevation -Zc, Weather criterion-K, DSO (static stability diagram), DDO (dynamic stability diagram).

DSO - gives a complete description of the ship's stability : transverse metacentric height, shoulder of static stability, limit angle of DSO, sunset angle of DSO.

DSO allows you to solve the following tasks:

the magnitude of the heeling moment from the displacement of the load and the overturning moment;
creation of the necessary exposure of the side for the repair of the hull, outboard fittings;
determination of the largest value of the statically applied heeling moment that the ship can withstand without capsizing, and the roll that it will receive in this case;
determination of the ship's roll angle from the instantaneously applied heeling moment in the absence of an initial roll;
determination of the roll angle from a suddenly applied heeling moment in the presence of an initial roll in the direction of the heeling moment;
determination of the angle of roll from a suddenly applied heeling moment in the presence of an initial roll in the direction opposite to the action of the heeling moment.
Determining the roll angle when moving cargo along the deck;
Determination of static overturning moment and static overturning angle;
Determination of dynamic overturning moment and dynamic overturning angle;
Determining the required heeling moment to straighten the vessel;
Determination of the weight of the cargo during the movement of which the ship will lose stability;
What can be done to improve the stability of the vessel.

Standardization of stability at the request of the Register of Shipping of Russia and Ukraine:

the maximum arm of the static stability of the DSO is more than or = 0.25 m with a maximum length of the vessel less than or = 80 m and more or = 0.20 m with a vessel length of more than or = 105 m;
diagram maximum angle more than or = 30 degrees;
sunset angle DSO more or = 60 degrees. and 55 degrees, taking into account icing

4. weather criterion - K more than or \u003d 1, and when sailing in the North Atlantic - 1.5

5. corrected transverse metacentric height for all loading options

should always be positive, and for fishing vessels not less than -0.05 m.

The roll characteristics of a vessel depend on the metacentric height. The greater the metacentric height, the sharper and more intense the pitching, which negatively affects the securing of the cargo and its integrity, and, in general, the safety of the entire ship.

Approximate value of the optimal metacentric height for various vessels in meters:

cargo-passenger large tonnage 0.0-1.2 m, medium tonnage 0.6-0.8 m.
dry cargo of large tonnage 0.3-1.5 m., medium tonnage 0.3-1.0 m.
large tankers 1.5-2.5 m.

For dry cargo ships of medium tonnage, four stability zones have been determined based on field observations:

A - roll zone or insufficient stability-h|B =0.0-0.02 - when such vessels turn at full speed, a list of up to 15-18 degrees occurs.

B - zone of optimal stability h|B=).02-0.05 – in rough seas, ships experience smooth rolling, crew habitability is good, lateral inertial forces do not exceed 10% of deck cargo gravity.

B - zone of discomfort or increased stability h|B=0.05-0.10 - sharp pitching, working and rest conditions for the crew are poor, lateral inertial forces reach 15-20% of the gravity of the deck cargo.

G-zone of excessive stability or destruction h|B more than 0.10 - transverse inertial forces on rolling can reach 50% of the gravity of the deck cargo, while the cargo is broken, deck rigging parts (rings, shells), the ship's bulwark are destroyed, which leads to loss of cargo and death of the ship.

The Ship's Stability Information usually gives complete stability calculations without icing:

100% ship's stores without cargo
50% ship's stores and 50% cargo, of which may be deck cargo
50% inventory and 100% cargo
25% ship's stores, no cargo, cargo on deck
10% ship stores, 95% cargo.

Taking into account icing, the same + with ballast in tanks.

In addition to calculating stability for typical loading cases with and without icing, information on stability allows you to conduct a complete calculation of the vessel's stability for non-standard loading cases. In this case, it is necessary:

Have an accurate picture of the location of cargo in cargo spaces in tons;
Data in tons for ship stock tanks: heavy fuel oil, diesel fuel, oil, water;
Compile a table of weights for a given vessel load, calculate the ship's CG moments

relative to the vertical and horizontal axes and applicates vertically and horizontally -

Calculate the sums of the weights (total displacement of the ship), the value of the longitudinal moment of the ship's CG (taking into account the signs + and -), the vertical static moment
Determine the applicate and abscissa of the ship's CG as the corresponding moments divided by the present gross displacement of the ship in tons
According to the amount of reserves in % and cargo in % according to the reference tables (limiting curve), it is rough to estimate whether the vessel is stable or not and whether there is a need to take additional sea water ballast into the ship's double-bottom tanks.
Determine boat's trim curves (see tables in Stability Information)
Determine the initial transverse metacentric height as the difference between the applicate of the center of magnitude - and the applicate of the center of gravity, select from the tables (applicate Information on Stability - hereinafter referred to as "Information") the free surface correction to the transverse metacentric value - determine the corrected transverse metacentric value.
With the calculated values of the ship's displacement for a given voyage and the corrected metacentric height, enter the diagram of the shoulders of the static stability curves (attached in the "Information") and after 10 degrees build a DSS of the static stability shoulders from the angle of heel at a given displacement (Reed's diagram)
From the DSO diagram remove all the main data according to the requirements of the Register of Shipping of Ukraine, Russia.
Determine the value of the conditional calculated roll amplitude for this loading case, using the recommendations in the reference data. Increase this amplitude by 2-5 degrees due to wind pressure (wind pressure of 6-7 points is taken into account). Taking into account all the acting factors simultaneously, this amplitude can reach values of -15-50 degrees.
Continue DSO in the direction of negative values of the abscissa and set aside the value of the calculated pitching amplitude to the left of the zero coordinates, then restore the perpendicular from the point on the negative value of the abscissa axis. By eye, draw a horizontal line parallel to the abscissa axis like this. So that the area to the left of the x-axis and to the right of the DSO are equal. (see example) - determine the shoulder of the overturning moment.
At the same time, remove the overturning moment arm from the DSO and calculate the overturning moment as the product of the displacement and the overturning moment arm.
According to the value of the average draft (calculated earlier), select the value of the heeling moment from additional tables (Information)
Calculate the weather criterion -K, if it meets the requirements of the Register of Shipping of Ukraine, including all the other 4 criteria, then the stability calculation ends here, but according to the requirements of the IMO Code of Stability for Vessels of All Types of -1999, it is required to additionally have two more stability criteria, which can only be determined from the DDO (Dynamic Stability Diagram). When the ship is sailing in icing conditions, calculate the weather criterion for these conditions.
The construction of DDO - dynamic stability diagrams is easier to perform on the basis of the DSO diagram, using the scheme of Table. 8 (p. 61 - L.R. Aksyutin "Cargo plan of the vessel" - Odessa-1999 or p. 22-24 "Stability control of sea vessels" - Odessa-2003) - to calculate the shoulders of dynamic stability. If, according to the diagram of limiting moments in the Information on Stability, the ship is stable according to our calculations, then it is not necessary to calculate DDO-.

According to the requirements of the IMO-1999 Stability Code (IMO Resolution A.749 (18) of June 1999)

· the minimum transverse metacentric height GM o -0.15 m for passenger ships, and for fishing - more than or equal to 0.35;

· shoulder of static stability not less than 0.20 m;

· maximum DSO with maximum static stability arm - more than or equal to 25 degrees;

· shoulder of dynamic stability at a roll angle of more than or plus 30 degrees - not less than -0.055 m-rad .; (meter)

shoulder of dynamic stability at 40 degrees (or flooding angle) not less than - 0.09 m-rad.; (meter)

Difference of dynamic stability shoulders at 30 and 40 degrees - not less than 0.03 m-rad. (meter)

· weather criterion more than or = one (1) - for ships more than or = 24 m.

· additional angle of heel due to constant wind for passenger ships not more than 10 degrees, for all other ships not more than 16 degrees or 80% of the angle at which the edge of the deck enters the water, depending on which angle is minimal.

On June 15, 1999, the IMO Navigational Safety Committee issued circular 920 - Model loading and stability Manual, which recommends that all states with a fleet provide all ships with a special Manual for calculating the loading and stability of the ship, in which to give the types of optimal load and stability calculations of the vessel, give all the symbols and abbreviations given at the same time, how to control the stability, landing of the vessel and its longitudinal strength. This manual contains all abbreviations and units for the above calculations, tables for calculating stability and bending moments.

In the sea verification of the transverse metacentric height of the vessel is carried out according to an approximate formula that takes into account the width of the vessel - B (m), the pitching period - To (sec) and C - coefficient from 0.6 - to 0.88, depending on the type of vessel and its load - h = (CB / To) 2 with an accuracy of 85-90% .(h-m).

To fulfill the RGZ on the subject "Transportation of special regime and dangerous goods", you can use the author's manual "Calculation of the ship's cargo plan" published by SevNTU.

Get a specific task for calculating the cargo plan from the teacher. Original

Information about the stability of the vessel is with the teacher. To perform calculations

for this vessel, the student needs to make copies of the calculation tables and graphs from the "Information". The use of other "Information on the stability of the vessel" during the marine production practice for one's own, specific vessel and transported cargo is allowed to be protected by the RGZ.

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