Linear trim. Longitudinal stability and trim. Changing the trim during longitudinal movement of the load
13. Sheerness the upper deck, which is a smooth rise of the deck from amidships to the bow and stern, also affects the appearance of the ship. A distinction is made between ships with standard sheer, determined according to the Load Line Rules, ships with reduced or increased sheer, and ships without sheer. Often shearing is not performed smoothly, but in straight sections with breaks - two or three sections over half the length of the vessel. Thanks to this, the upper deck does not have a double curvature, which simplifies its manufacture.
The deck line of seagoing vessels usually looks like a smooth curve with a rise from the middle part in the direction of the bow and stern and forms the sheerness of the deck. The main purpose of sheer is to reduce flooding of the deck when the ship is sailing in rough seas and to ensure unsinkability when its ends are flooded. River and sea vessels with great height As a rule, they do not have sheer freeboard. The rise of the deck at the stern is established based, first of all, on the conditions of non-flooding and unsinkability.
14.Die- this is the slope of the deck from the DP to the sides. Typically, decks have open decks (upper and superstructure decks). Water falling on the decks, due to the presence of debris, flows to the sides and from there is discharged overboard. The drop point (the maximum elevation of the deck in the DP relative to the side edge) is usually taken equal to V50 of the vessel's width. In cross section, the loss is a parabola; sometimes, to simplify the technology of manufacturing the body, it is formed in the form of a broken line. Platforms and decks lying below the upper deck are not damaged. The midship frame plane divides the ship's hull into two parts - bow and stern. The ends of the body are made in the form of stems (cast, forged or welded). Nasal
When a submarine floats, the equality between its weight and the supporting force (buoyancy) is gradually violated. The weight of the bow and stern relative to each other also changes, which leads to the appearance of trim.The supporting force is equal to the product of the density of water and the submerged waterproof volume of the submarine's pressure hull. The density of sea water depends on salinity, temperature and pressure. The volume of the pressure hull also changes and depends on the depth of immersion and the temperature of the sea water, the weight of the submarine depends on the consumption of variable cargo: fuel, oil, ammunition, fresh water, provisions, etc. Most of these cargo are replaced by sea water, including fuel.
The difference in the densities of fuel and water leads to an imbalance. As a result, the equality between the weight of the submarine and the supporting force is violated, which leads to the emergence of so-called residual buoyancy. If the supporting force is greater than the weight of the submarine, then the residual buoyancy will be positive; if less, it will be negative. With positive residual buoyancy, the submarine tends to float, with negative residual buoyancy, it tends to sink.
Uneven consumption of variable loads in the bow and stern parts of the boat leads to the formation of trims.
Bringing residual buoyancy and trim to specified values by receiving (removing) water from overboard into the surge tank and moving water between trim tanks is called trimming.
The above and other reasons make it necessary to periodically trim the submarine.
Trimming can be done without moving or while moving.
Trim without travel
Trimming without stroke is performed:When the submarine has not dived for a long time;
In areas where it is difficult to maneuver underwater;
At the sign;
For educational purposes.
When the sea state is no more than 3-4 points, trim without running is usually performed at periscope depth, and when the sea state is over 4 points - at safe depths.
The advantage of trim without running is that this method allows you to trim a submarine in an area with shallow depths. The disadvantages include: the need for trim when underway and ensuring external security in areas that are difficult to maneuver.
It is advisable to trim at periscope depth with a obviously lightweight submarine, for which, before immersing in the surge tank, it is necessary to take in water that is 5-10 tf less than the calculated value (depending on the design of the submarine). The main ballast is received first in the end groups, then in the middle. If, after filling the end groups of the main ballast tanks, the submarine has a trim of more than 0.5°, the trim moment should be extinguished by distilling water from one trim tank to another. After filling the middle group of main ballast tanks, trim begins.
Positive buoyancy, depending on the value, is extinguished by the intake of water from overboard into the equalization tank through the kingston or precise filling valve. To remove air bubbles from the end groups of the main ballast tanks and from the superstructure, the submarine must be “rocked,” that is, the trim must be moved from one end to the other, distilling water between the trim tanks, and then the ventilation valves of these tanks must be closed. With the removal of air bubbles from the tanks of the end groups, the tanks of the middle group are ventilated in the same way. It is recommended to stop distilling water from one trim tank to another when the trim does not reach the specified value by 1.5-2°.
In a submerged position, the nature of the residual buoyancy is judged by the readings of depth gauges. If a submarine sinks, it has negative residual buoyancy. To bring the boat to zero buoyancy, water from the surge tank is pumped overboard. If a submarine floats, it has positive residual buoyancy. To bring it to zero buoyancy, water is taken into the surge tank from overboard. Trimming without progress is considered completed if the submarine maintains a constant depth with a given trim for some time. At the end of the trim, the actual amount of water in the auxiliary ballast tanks is measured and recorded, as well as the personnel available in each compartment and conning tower are checked and recorded.
Trim on the move
Performed in areas that allow the submarine to maneuver freely underwater. In calm sea conditions, trimming can be done at periscope depth, and in rough conditions - at safe depth.To understand the essence of trim and control of a submarine in an underwater position, you need to know the principle of operation of horizontal rudders and the forces acting on the submarine.
When repositioning the horizontal rudders while moving (Fig. 3.1), hydrodynamic forces of the stern Rк and bow Rн horizontal rudders arise.
Rice. 3.1. Forces arising when shifting horizontal rudders
These forces are proportional to the square of the submarine's speed and the rudder angles. The forces Rк and Rн can be replaced by their components parallel to the GX and GY axes. The forces Rxk and Rxh increase the resistance of water to the movement of the submarine. The forces Ruk and Ryn change the trim and direction of the submarine in vertical plane.
According to the well-known theorem of theoretical mechanics, the forces RyK and RyH can be represented as applied at the center of gravity of the submarine with the simultaneous action of hydrodynamic moments of the horizontal rudders Mk and Mn. Shifting the stern horizontal rudders to dive gives a moment - Mk, which trims the submarine to the bow, and a lifting force +Ruk. repositioning the bow horizontal rudders for ascent gives a moment +Mn, which trims the submarine aft, and a lifting force +Ryn
Shifting the stern horizontal rudders for ascent gives a trimming moment at the stern +Mk and a sinking force _RyK, and shifting the bow horizontal rudders for a dive gives a trimming moment at the stern - Mn and a sinking force -Rk.
Rice. 3.2. Forces acting on a submarine while moving underwater
The joint use of horizontal rudders creates a trim moment and force applied to the center of gravity of the submarine, which are the resultant trim moments and forces created separately by the stern and bow horizontal rudders.
A submarine having a steady speed Vpl in a submerged position is subject to static and dynamic forces (Fig. 3.2). Static forces include the weight force, the supporting force and their moments, which act on the submarine constantly. These forces are usually replaced by the resultant - residual buoyancy Q and its moment Mq. With longitudinal inclinations (trim φ), a restoring moment Mψ occurs, which tends to return the submarine to its original position.
Dynamic forces and moments include thrust force, propeller thrust moment, and hydrodynamic forces and moments. The thrust force of the propellers Tt is proportional to the speed of rotation of the propeller. During steady motion, the thrust force of the propeller is balanced by the drag. The thrust moment of the propellers Mt arises due to the fact that the axes of the shaft line on a submarine usually do not coincide in height with the center of gravity and are located below it. Therefore, the moment of thrust force of the propellers trims the submarine to the stern.
Hydrodynamic forces arise when a submarine moves. For practical trimming, it can be assumed that at a constant depth the resultant of the hydrodynamic forces Rm acting on the hull is proportional to the speed and trim angle. Point K, applied to the resultant Rm, is called the center of pressure. The center of pressure does not coincide with the submarine's center of gravity and is usually located forward of it.
Based on the theorem of theoretical mechanics mentioned above, the effect on the submarine of the resultant hydrodynamic forces can be represented as a force Rm applied to the center of gravity G of the submarine and a moment MR. The force Rm can be broken down into its components. The component Rmх (drag) characterizes the resistance of water to the movement of a submarine. The Rm component plays an important role in the controllability of a submarine in the vertical plane. At a constant diving depth with a trim near zero or at the stern, the lifting force Rmu, and the moment MR trims the submarine to the stern; with a trim to the bow, the force Rtu is sinking, and the moment MR trims the submarine to the bow.
The basis for trim while moving is the movement of the submarine at a constant depth and on a straight course, as this makes it possible to determine the direction of forces and moments. Determining the direction of forces and moments in practice is facilitated by knowledge of the following characteristic positions of an undifferentiated submarine sailing at a constant depth, depending on the angles of the horizontal rudders and trim:
Trim 0° - the stern horizontal rudders are shifted to float;
Trim 0° - the stern horizontal rudders are shifted to submersion;
The trim is on the bow - the stern horizontal rudders are shifted to submersion;
The trim is on the bow - the stern horizontal rudders are shifted to float;
Trim to the stern - the stern horizontal rudders are shifted to float;
Trim to the stern - the stern horizontal rudders are shifted to submersion.
Examples of trim on the move
Example 1. The submarine on a direct course moves at low speed, maintains a constant depth with a trim of 0°.
Rice. 3.3. The submarine has a heavy bow
The stern horizontal rudders are set to float 12°, the bow rudders are at zero. It is possible to differentiate the submarine (Fig. 6.6).
The stern horizontal rudders create a trimming moment at the stern +MK and a sinking force - RyK. The +MK moment strives to create a trim to the stern, but the submarine has zero trim. It follows from this that there is some moment that counteracts the +MK moment to create trim aft. Such a moment may arise due to the fact that the bow of the submarine is heavier than the stern or, which is the same thing, the stern is light, i.e. the submarine has an excess trimming moment on the bow - Mid. To trim a submarine by moment, you should move water from the bow trim tank to the stern tank and at the same time move the stern horizontal rudders to zero.
It is impossible to determine in practice the nature of the residual buoyancy in this case, since the direction of the force Q, the resultant of the forces of weight and buoyancy, is unknown. Since the submarine maintains a given depth, the residual buoyancy can be:
Zero when the forces Rmy and Ryк are equal in magnitude;
Negative if Rmу > Rvк;
Positive if Rmu
Residual buoyancy in this case can only be revealed later in the process of differentiating the submarine according to new instrument readings.
Example 2. The submarine on a direct course moves at low speed, maintains a constant depth with a trim of 5° on the bow. The stern horizontal rudders are shifted to float 12° to the bow, the bow rudders are in the plane of the frame (at zero). It is necessary to trim the submarine (Fig. 3.4).
The stern horizontal rudders create a trimming moment at the stern +MK and a sinking force - RyK. The trim to the bow creates a sinking force - Rm, and a moment -MR, which trims the submarine to the bow. The submarine maintains a constant depth, but under the influence of sinking forces it must sink, therefore, there is a force that prevents it from sinking. In this case, such a force can only be residual positive buoyancy, i.e. the submarine is light. The +MK moment, as in example 1, is prevented from creating a trim at the stern by the excess trim moment at the bow - Mid, i.e. the submarine has a heavy bow.
With this characteristic position of an undifferentiated submarine, it is necessary to first move water from the bow to the stern, while moving the stern horizontal rudders to submerge to keep the submarine at a constant depth, and then take water from overboard into the surge tank for trimming by buoyancy.
Rice. 3.4. The submarine is light, the bow is heavy
An attempt to trim the submarine first by buoyancy and then level the trim may lead to the fact that it will not be possible to maintain it at a given depth. In fact, with the start of receiving water from overboard, the submarine will begin to sink due to an increase in its weight. To maintain a given depth, you will have to reduce the trim on the bow, i.e., reduce the sinking force -Rm, for which it is necessary to shift the horizontal rudders to ascent. But, since the horizontal rudders are shifted only to a limited angle and already have 12° for ascent, shifting them to the full angle for ascent (up to the limiter) may not reduce the trim on the nose to the required value. Consequently, the submarine will submerge.
In the same way, forces and moments are analyzed and trim is performed on the move in other characteristic positions of an untrimmed submarine.
In practice, trim on the move is performed as follows. After the personnel occupy the places according to the diving schedule, the conning hatch is battened down, the electric motors are given a low speed and the main ballast is received, after which the command is given: “Trim the submarine at a depth of so many meters, at such and such a speed, with a trim of so many.” degrees bow (aft).” The main ballast is received, as during trimming, without stroke. The ventilation of the middle group of main ballast tanks is closed at a depth of 5-7 m. The specified trim depth is maintained by the stroke and trim. When going to depth, significant trim should not be created. The ventilation of the end tanks of the main ballast is closed immediately upon the arrival of the submarine at a given depth (after transferring the trim from bow to stern).
If, after filling the middle group of main ballast tanks, the submarine receives negative buoyancy, you should create a trim to the stern with horizontal rudders and stroke and, holding the boat at a given depth, simultaneously pump out water from the surge tank.
If this turns out to be insufficient, give a bubble to the middle group of tanks or blow it out, pump out the required amount of water from the surge tank and, having removed the bubble from the middle group of tanks, continue trimming. These measures are taken depending on the speed of the submarine's dive.
If the submarine does not submerge, water should be taken into the surge tank through the seacock or precision filling valve. As soon as the depth gauge shows a change in depth, water intake is suspended.
To remove air bubbles from the end tanks of the main ballast and from the superstructure, it is necessary to alternately trim the submarine to the bow and stern (“rock” the submarine), and then close the ventilation valves of the end groups of the main ballast tanks.
In order to correctly and quickly differentiate the submarine by the position of the horizontal rudders and trim, the residual buoyancy and excess trim moment are determined, after which they begin trimming.
If the trimming officer does not have sufficient experience, the following rules must be followed:
1. If the submarine maintains a given depth and its trimming moment from the horizontal rudders coincides with the trim, you should first trim it by buoyancy, and then by trim.
2. If the submarine maintains a given depth, but the trim does not coincide with the trimming moment of the horizontal rudders, you should first trim it by trim, and then by buoyancy.
By draining or receiving water into the equalization tank and pumping auxiliary ballast between the trim tanks, a position is achieved so that the bow horizontal rudders are at zero, and the stern ones are with a slight deviation from the plane of the frame. In this case, the submarine with a slight trim to the bow should maintain depth. In this position it is considered differentiated.
At the end of the trim, the ventilation valves of the main ballast tanks are opened and closed (“slammed”) to bleed the remaining air cushion. Having made sure that at a given speed the submarine maintains a constant depth on a straight course with zero or a given trim, the shift of the stern horizontal rudders does not exceed ±5°, and the bow rudders lie at zero, the command “Trim is complete” is given. The compartment commanders report to the central post about the presence of personnel in the compartments and the amount of water in the auxiliary ballast tanks. This data is recorded in the log and trim logs.
Vessel trim (from Latin differens, genitive case differentis - difference)
tilt of the ship in the longitudinal plane. D. s. characterizes the landing of the vessel and is measured by the difference between its draft (deepening) stern and bow. If the difference is zero, the ship is said to be “sitting on an even keel”; if the difference is positive, the ship is trimmed to the stern; if it is negative, the ship is trimmed to the bow. D. s. affects the maneuverability of the vessel, operating conditions of the propeller, maneuverability in ice, etc. D.s. There are static and running, which occurs at high speeds. D. s. usually regulated by the intake or removal of water ballast.
Big Soviet encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .
See what “ship trim” is in other dictionaries:
TRIM of the vessel- Origin: from lat. differens, differentis the difference in the inclination of the vessel in the longitudinal plane (around the transverse axis passing through the center of gravity of the waterline area) ... Marine encyclopedic reference book
- (Trim difference) the angle of longitudinal inclination of the vessel, causing a difference in drafts of the bow and stern. If the depth of the bow and stern is the same, then the ship sits on an even keel. If the recess of the stern (bow) is larger than the bow (stern), then the ship has... ... Marine dictionary
- (Latin, from differe to distinguish). The difference in the depth of immersion in water between the stern and bow of a ship. Dictionary of foreign words included in the Russian language. Chudinov A.N., 1910. DIFFERENT lat., from differre, to distinguish. Difference in stern immersion in water... ... Dictionary of foreign words of the Russian language
- (ship) the inclination of the ship in the longitudinal vertical plane relative to the surface of the sea. It is measured by trim meters in degrees for a submarine or the difference between the recesses of the stern and bow for surface ships. Affects agility... ...Nautical Dictionary
- (from Latin differens difference) the difference in the draft (deepening) of the vessel bow and stern... Big Encyclopedic Dictionary
Marine term, the angle of deviation of the ship's hull from the horizontal position in the longitudinal direction, the difference in the draft of the stern and bow of the ship. In aviation, to denote the same angle that defines the orientation aircraft, the term is used ... ... Wikipedia
A; m. [lat. differens] 1. Special. The difference in the draft of the bow and stern of the ship. 2. Finance. The difference in the price of a product when ordering and receiving it during trading operations. * * * trim (from the Latin differens difference), the difference in the draft (deepening) of the vessel... ... encyclopedic Dictionary
Trim- DIFFERENT, the difference in the depth (landing) of the vessel bow and stern; if, for example, the stern is deepened by 1 ft. more than the bow, then they say: the ship has a depth of 1 ft at the stern. D. had a special meaning in the sail. fleet, where a good sailing ship d.b. have D. on… … Military encyclopedia
- [from lat. differens (differentia) difference] of the vessel, the inclination of the vessel in the longitudinal plane. D. determines the landing of the ship and is measured by the difference between the drafts of the stern and bow. If the difference is zero, the ship is said to be sitting on an even keel; if the difference... Big Encyclopedic Polytechnic Dictionary
Trim of the ship (vessel)- the tilt of the ship (vessel) in the longitudinal plane. It is measured using a trim meter as the difference between the draft of the ship and the stern in meters (for submarines in degrees). Occurs when rooms or compartments at the ends of a ship are flooded, unevenly... ... Glossary of military terms
When operating a displacement vessel, monitoring the running trim is just as important as on a planing vessel.
It is not always possible to arrange a vessel during design and load it when setting sail in such a way as to ensure optimal alignment and optimal trim. As is known, excessive running trim leads to loss of speed and worsens economic performance.
I encountered this problem when I began testing my displacement boat “Duckling”, converted from a small (No. 1) lifeboat (length - 4.5 m; width - 1.85 m). As soon as I gave full throttle to the SM-557L engine, the stern trim immediately increased to values clearly exceeding the permissible 5-6°: wave formation increased, but the speed did not increase.
I began to look for a way to reduce the running trim. By analogy with high-speed boats, I decided to use transom plates. I cut out two transom plates of different shapes with variable angles of inclination from bakelized plywood and tested them one by one on the “Duckling”. The very first outputs showed that at small angles of inclination the plates are ineffective, and at large angles the trim is indeed reduced, but at the same time they begin to work as a brake. When sailing on a following wave, strong yaw appears due to the plates; in reverse, the plate blocks the flow of water to the propeller. Be that as it may, but having a power of 13.5 hp. s., it was not possible to reach a speed above 10 km/h either with or without plates. The relative speed - the Froude number along the length - fluctuated somewhere around 0.4.
After unsuccessful trials of transom plates, I decided to try installing a specially profiled ring attachment on the propeller. The nozzle that deflects the jet downwards from the propeller, according to my calculations, was supposed to not only create additional lift on the hull, reducing the running trim, but also at the same time increase the efficiency of the propeller, since the SM-557L engine develops too much big number rpm for possible speed.
The Utenka propeller shaft has an inclination relative to the vertical line of about 8°. The front part of the nozzle - from the nose edge to the plane of the propeller disk - is made coaxially with the propeller shaft. In the plane of the propeller disk, the axial line of the nozzle has a kink - it is inclined downward by 8° (here the angle of inclination to the vertical line is already 16°).
As can be seen from the diagram, behind the plane of the screw disk in the upper part of the nozzle, its internal generatrix looks like a straight line. The resulting force P c is decomposed into the thrust force and the lifting force. The thrust force was measured with a dynamometer and turned out to be equal to 200 kgf. The lifting force P p, which directly reduces the running trim, is approximately equal to 57 kgf.
Now about making the nozzle. Trapezoidal slats were cut from polystyrene foam, which were then glued into a cylinder using epoxy glue. Processing was carried out with a sharp knife and rasp and checking the profile using templates. The outside of the finished nozzle was covered with two layers of fiberglass with epoxy glue. The inner surface of the nozzle is covered with epoxy putty, into which flake graphite is rubbed in to reduce friction.
Two aluminum angles are fixed at the top and bottom, tightened with M6 bolts. These bolts and circular slings made of 0 2 mm steel cable securely fasten the nozzle and squares into one piece. The front ends of the squares are attached to the sternpost, the rear ends to the rudder post (ruder post).
The ends of the propeller blades are cut to the inner diameter of the nozzle with an annular gap of 2-3 mm.
I have already successfully completed two navigations with the “Duckling” attachment. During this period the following was established:
- speed increased from 10 to 12 km/h (Froude number approx. 0.5);
- running trim is practically absent;
- even on a steep following wave, the boat obeys the rudder well, and the propeller is almost not exposed;
- The boat moves reliably and satisfactorily obeys the rudder in reverse.
Installing an outboard motor on any displacement boat, be it a fofan, a tuzik or a four-oared yawl, always causes a strong trim to the stern, which increases with increasing speed. In an article about the Pella boat, it was noted that its speed under the Veterok engine (8 hp) is 9.16 km/h when the driver sits on the stern bank, and 11.2 km/h when he sits in the nose. Here is a clear indicator of how the running trim affects speed. But there are other disadvantages of such a landing. It is enough to mentally draw a straight line from the eyes of the helmsman sitting at the stern forward through the top point of the stem to make sure that objects on the water ahead are not visible to him. With such poor visibility along the course, the operation of any vessel is prohibited. Two options can be proposed; put in bow boat ballast or install an attachment on the propeller.
If factories producing outboard motors master the production of profiled anti-trim nozzles, a lot of gasoline will be saved, and most importantly, the operating conditions of boats will improve and navigation safety will increase; in any case, the risk of collision with floating obstacles will be reduced.
After obtaining the value of the average MMM draft, corrections for trim are calculated.
1st trim correction(correction for the displacement of the center of gravity of the current waterline - Longitudinal Center of Flotation (LCF).
1st Trim Correction (tons) = (Trim*LCF*TPC*100)/LBP
Trim - ship trim
LCF - displacement of the center of gravity of the effective waterline from the midships
TRS - number of tons per centimeter of sediment
LBP - distance between perpendiculars.
The sign of the correction is determined by the rule: the first trim correction is positive if the LCF and the greater of the bow and stern draft are on the same side of the midsection, which can be illustrated by Table 3.3:
Table 3.3. LCF correction signs
| Trim | LCF nose | LCF feed |
| Stern | - | + |
| Nose | + | - |
Note - It is important to remember the principle: when loading (increasing draft) the LCF always moves aft.
2nd trim correction(Nemoto correction, the sign is always positive). It compensates for the error arising from the displacement of the LCF position when the trim changes (18).
2nd Trim Correction (tons) =(50*Trim*Trim*(Dm/Dz))/LBP
(Dm/Dz) - the difference in the moment that changes the ship's trim by 1 cm at two drafts: one 50 cm above the average recorded draft, the other 50 cm below the recorded draft.
If the ship has hydrostatic tables in the IMPERIAL system, the formulas take the following form:
1 st Trim Correction =(Trim*LCF*TPI*12)/LBP
2nd Trim Correction =(6*Trim*Trim*(Dm/Dz))/LBP
Correction for sea water density
Ship hydrostatic tables are compiled for a certain fixed density of sea water - at sea vessels usually by 1.025, on river-sea vessels either by 1.025, or by 1.000, or by both density values at the same time. It happens that tables are compiled for some intermediate density value - for example, 1.020. In this case, it becomes necessary to bring the data selected from the tables for calculation into line with the actual density of sea water. This is done by introducing a correction for the difference between the tabulated and actual densities of water:
Amendment=Displacement table *(Density measured - Density table)/Density table
Without correction, you can immediately obtain the displacement value adjusted to the actual density of sea water:
Displacement fact = Displacement table * Density measured / Density table
Displacement calculation
After calculating the values of the average vessel draft and trim, the following is performed:
Based on the ship's hydrostatic data, the vessel's displacement corresponding to the average MMM draft is determined. If necessary, linear interpolation is used;
The first and second corrections “for trim” to the displacement are calculated;
The displacement is calculated taking into account corrections for trim and corrections for the density of sea water.
Calculation of displacement taking into account the first and second corrections for trim is carried out according to the formula:
D2 = D1 + ?1 + ?2
D1 - displacement from hydrostatic tables corresponding to the average draft, t;
1 - first correction for trim (can be positive or negative), t;
2 - second correction for trim (always positive), t;
D2 - displacement taking into account the first and second corrections for trim, i.e.
The first trim correction in the metric system is calculated using formula (20):
1 = TRIM × LCF × TPC × 100 / LBP (20)
TRIM - trim, m;
LCF - abscissa value of the center of gravity of the waterline area, m;
TPC is the number of tons by which the displacement changes when the average draft changes by 1 cm, t;
1 - first amendment, ie.
The first correction for trim in the imperial system is calculated using formula (21):
1 = TRIM × LCF × TPI × 12 / LBP (21)
TRIM - trim, ft;
LCF - abscissa value of the center of gravity of the waterline area, ft;
TPI - the number of tons by which the displacement changes when the average draft changes by 1 inch, LT/in;
1 - first amendment (can be positive or negative), LT.
The TRIM and LCF values are taken without taking into account the sign, modulo.
All calculations in the imperial system are performed in imperial units (inches (in), feet (ft), long tons (LT), etc.). The final results are converted to metric units (MT).
The sign of the correction?1 (positive or negative) is determined depending on the location of the LCF relative to the midsection and the trim position (bow or stern) in accordance with Table 4.1
Table 4.1 - Correction signs?1 depending on the position of the LCF relative to the midsection and trim direction
where: T AP - draft at the perpendicular, at the stern;
T FP - draft at the perpendicular, at the bow;
LCF is the abscissa value of the center of gravity of the waterline area.
The second amendment in the metric system is calculated using formula (22):
2 = 50 × TRIM 2 × ?MTC / LBP (22)
TRIM - trim, m;
MTS - the difference between MCT 50 cm above the average draft and MCT 50 cm below the average draft, tm/cm;
LBP is the distance between the bow and stern perpendiculars of the vessel, m;
The second amendment in the imperial system is calculated using formula (23):
2 = 6 × TRIM 2 × ?MTI / LBP (23)
TRIM - trim, ft;
LBP - the distance between the bow and stern perpendiculars of the vessel, ft;
MTI - difference between MTI 6 inches above average draft and MTI 6 inches below average draft, LTm/in;
LBP - the distance between the bow and stern perpendiculars of the vessel, ft.
All calculations in the imperial system are performed in imperial units (inches (in), feet (ft), long tons (LT), etc.). The final results are converted to metric units.
The displacement, taking into account the correction for the density of sea water, is calculated using formula (24):
D = D 2 × g1 / g2 (24)
D 2 - displacement of the vessel taking into account the first and second corrections for trim, t;
g1 - density of sea water, t/m 3 ;
g2 - tabular density (for which displacement D 2 is indicated in hydrostatic tables), t/m3;
D - displacement taking into account corrections for trim and density of sea water, m.
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