The displacement of a ship is the mass of water in tons displaced by the hull to the permissible load waterline, which, according to Archimedes' law, is equal to the mass of the ship. The weight of the vessel consists of the vessel's own weight and its carrying capacity (payload weight).

The vessel's light weight includes:

ship hull equipped with inventory and spare parts;

ready-to-use power plant with inventory and spare parts;

water in boilers, pipelines, pumps, condensers, coolers;

fuel in all operational pipelines;

carbon dioxide and brine or other operating materials in refrigeration units and fire protection systems;

residual water in bilges and tanks that cannot be removed by pumps, as well as waste water and moisture.

Carrying capacity in tons with hold volume and operating speed is the most important economic characteristic of a vessel; it must be guaranteed by the shipyard, since underestimation is punishable by contractual penalties.

Gross deadweight - the ship's deadweight - includes all masses that do not relate to the lightship displacement of the ship, such as:

payload (including mail);

crew and passengers with luggage;

all operating materials (fuel reserves, lubricants, oils, boiler feed water) in storage tanks;

ship supplies such as paints, kerosene, wood, resin, ropes;

supplies for the crew and passengers (drinking water, water for washing and provisions);

cargo securing equipment such as wooden supports, tarpaulins and masts, bulkheads for bulk cargo;

special equipment for special types of vessels, for example fishing equipment (nets, cables, trawls).

There are certain relationships between the most important components of the load, which also affect the efficiency of ships.

The ratio of a ship's light-laden displacement to its fully loaded displacement depends mainly on the type of vessel, the area of ​​navigation, the speed of the vessel and the design of the hull.
For example, the displacement of a light-laden cargo ship at normal operating speed (14 - 16 kts) without ice reinforcements is approximately 25% of the displacement when fully loaded.

The icebreaker, which must have powerful engines and a particularly reinforced hull, has a light displacement of approximately 75% of its total displacement.
If a cargo ship has a full displacement of 10 thousand tons, then the lightship displacement is approximately 2.5 thousand tons, and its deadweight is approximately 7.5 thousand tons, while a large icebreaker of the same displacement has a lightship displacement of approximately 7.5 thousand tons and deadweight 2.5 thousand tons.

The ratio of the mass of the power plant to the total displacement is determined by the speed of the vessel, the type of engine (diesel, steam turbine, diesel-electric plant, etc.), as well as the type of vessel. An increase in the speed of the vessel with the same type of installation always leads to an increase in engine power and, consequently, to an increase in the named ratios.

Ships with a diesel installation have a larger engine weight than ships with other types of installations. Since the power plant also includes auxiliary mechanisms for the production of electrical energy and power plants for refrigerators, the mass of power plants on passenger, refrigerator and fishing vessels is greater than the mass of installations on conventional cargo ships of the same displacement.
Thus, the mass of the power plant of cargo ships is 5 - 10%, passenger ships - 10 - 15%, fishing ships 15 - 20%, and tugs and icebreakers, as a rule, even 20 - 30% of the total displacement.

The ratio of the mass of the ship's hull to its displacement is determined by the mass of the bare hull of the ship and the mass of its equipment. All these masses depend on the type of vessel and, therefore, on its purpose.
The mass of a ship’s hull is affected not only by its main dimensions and their ratios, but also by the volume of superstructures and ice reinforcements. The casting system and the use of high-strength structural steels also play a significant role, especially for ships longer than 160 m.

The weight of the equipment depends on the purpose of the vessel; for example, in passenger ships due to passenger cabins, public, utility rooms, etc., or in fishing vessels (fishing and processing) due to crew cabins, fish processing machines and refrigerator equipment, it is significantly greater than that of conventional cargo ships and tankers.

The ratio of deadweight to total displacement (displacement utilization rate per deadweight) best characterizes the efficiency of cargo ships (not to mention the speed of the vessel). For tugs and icebreakers, the deadweight primarily determines the cruising range (voyage duration), since the deadweight of these types of ships is spent mainly on fuel materials and supplies.

The highest displacement utilization rates by deadweight are cargo ships and tankers (from 60 to 70%), the smallest are tugs and icebreakers (from 10 to 30%).

Deadweight or gross load capacity is the maximum amount of cargo a ship can accept when diving to the load line. Consists of all cargo, fuel, water reserves and supply weight.

180. What is the cargo capacity of a ship?

This is the volume of all cargo spaces. There is a distinction between grain and bale cargo capacity. The difference between them is 6 – 10%.

181. What is full register capacity?

This is the volume of ship spaces under the upper deck and in permanently covered superstructures in registered tons, obtained as a result of measuring the ship. It includes the capacity of the wheelhouse, galley, bathrooms, double bottom, water tanks.

What is net register capacity?

This is the volume determined by deducting from the total registered capacity the volume of all residential, household premises, and auxiliary machinery premises outside the engine room. It is measured in a registered ton equal to 2.63 cubic meters.

Is pressing of water tanks allowed at low temperatures?

At low temperatures, pressing water tanks, including ballast tanks, is not allowed, because If ice plugs form in the air ventilation and measuring pipes, it will become impossible to empty and fill the tanks without thawing the plugs. Filling tanks is allowed to no more than 95% of its capacity.

Basic principles of the hydrodynamic theory of lubrication.

The essence of this theory is as follows. When at rest, the shaft journal is in contact with the bottom of the bearing (a wedge-shaped gap is formed between them) through a thin layer of adhered oil particles. When the shaft rotates, due to the difference in the diameters of the journal and bearing, a wedge-shaped gap is formed between them, into which oil adhering to the rotating journal of the shaft is drawn. In the narrow part of the gap, pressure is created, lifting the shaft. The maximum pressure value corresponds to an arc of up to 120 degrees of the bearing circumference.

Thus, at a certain rotation speed, an oil layer is formed between the surfaces of the journal and the bearing, and the shaft does not touch the bearing walls. The external load on the journal is balanced by the internal pressure of the oil wedge, the magnitude of which increases with increasing shaft speed. This can be explained by the fact that with increasing rotation speed, the thickness of the wedge-shaped gap increases due to an increase in the amount of oil pumped by the shaft journal.

The friction between the oil layers depends only on the viscosity of the oil and does not depend on the bearing material and the degree of roughness of its surfaces. However, it should be borne in mind that, in accordance with the laws of hydrodynamic friction, the viscosity of the oil is directly proportional to the load and the size of the gap between the shaft and the bearing.

In a properly designed bearing, during engine operation, a hydrodynamic regime is established, which is characterized by self-regulation between oil viscosity and friction force. Indeed, with increasing angular velocity, the friction force between the oil layers increases, which leads to strong heat generation. As the temperature increases, the viscosity of the oil decreases, and the process between friction force and temperature stabilizes.

What is the permissible diameter of the receiving mesh holes on the drainage system?

Receiving drainage branches must be equipped with receiving boxes or nets with holes with a diameter of 8 - 10 mm.

What response pressure is the safety valve of hydraulic systems set to?

Hydraulic mechanisms must be protected by safety valves, the response pressure of which should be no more than 1.1 times the maximum design pressure.

When there is a decrease in the performance of the evaporation unit, measures should be taken to clean the heating elements?

When performance decreases by more than 20% of the nominal .

To what pressure should the safety device of mechanically driven air compressors be adjusted?

A safety valve must be installed at each stage of the compressor, which does not allow the pressure in the stage to increase more than 1.1 calculated when the valve on the discharge pipeline is closed.

The valve must be designed so that it cannot be adjusted or switched off after installation on the compressor.

What requirements must devices for heating fuel in tanks meet?

Liquid fuel can only be heated using steam or water coils.

Fuel heating coils should be located in the lowest parts of the tanks.

The ends of the receiving fuel pipes in supply and settling tanks should be located above the heating coils in such a way that, if possible, the coils are not exposed.

The maximum temperature of heated fuel in tanks must be at least 10 degrees Celsius below the flash point of fuel vapor.

The heating steam condensate must be directed to a control tank with a sight glass.

The steam pressure used to heat the fuel should not exceed 7 kg/sq. cm (0.7 MPa).

To monitor the temperature of the heated fuel, thermometers must be installed in the required places.

What should be the capacity of the overflow tank?

The capacity of the fuel overflow tank must be at least 10 minutes of capacity of the fuel transfer pump.

The overflow tank must be equipped with a light and sound alarm that is triggered when it is filled over 75%.

Under what conditions should emergency power supplies maintain long-term functionality?

Emergency power supplies must remain operational under the following conditions: - long-term roll of 15 degrees;

Long trim 5 degrees;

Rolling +\- 22.5 degrees with a period of 7-9 seconds;

Pitching +\- 7.5 degrees;

Simultaneous action of roll of 22.5 degrees and trim of 10 degrees.

What is the required amount of contact between the gear teeth of the main mechanisms?

The contact of the gear drives of the main mechanisms must be at least 90% in forward motion, and in reverse 70% along the length and 60% in the height of the teeth.

What is the circulation ratio in a condenser?

This is the ratio of the amount of cooling water passing through the condenser to the amount of condensate formed:

M = ----- ; Usually M=100 – 110

Dk

Under what fluctuations in the supply air should pneumatic devices and elements operate reliably?

Pneumatic devices and elements must operate reliably with supply air fluctuations of +\- 20%.

What is the minimum height of oil pressure tanks in gravity lubrication systems for stern tube bearings?

The bottoms of tanks must be at least 3 meters above the highest load waterline.

Under what conditions can the steering gear stock be allowed to operate when twisted by 5 degrees or more?

The stock can be allowed to operate provided it is annealed and the sector or tiller is replaced with a new key.

At what temperature should circulation oil separation be carried out?

Separation of oils containing additives should be carried out without washing with water and at a heating temperature of no more than 90 degrees Celsius (the upper limit is preferable for oils with high detergent properties). It is recommended to separate oils without additives by washing with water at a heating temperature of no more than 75°C.

What is the frequency of manual cleaning of the separator drum, and the permissible load on the surface of the working plates?

The frequency of manual cleaning of the separator drum should be determined in each specific case, depending on the nature of the released suspension, the productivity and sludge volume of the drum; Sludge deposits on the drum walls must not be allowed to reach the edge of the plate stack. The permissible contamination of the surface of the work plates should not exceed 30%.

What speed should the drive provide for pulling out the anchor chain when the anchor approaches the lock?

How many links should the anchor chain link consist of?

When lifting and releasing the anchor, all connecting brackets of the anchor chain must lie flat on the windlass (capstan) chain drum sprocket. To do this, each link of the anchor chain must consist of an odd number of links (not counting the connecting brackets).

At what reduction in diameter should anchor chain links be replaced?

Links must be replaced when the average diameter in the most worn part decreases by 1/10 or more of the original nominal diameter.

When should a mooring line be replaced?

A steel mooring cable must be replaced if it has broken wires of more than 10% of their total number over a length of the cable equal to eight of its diameters.

What is the time for shifting the propeller propeller blades from full forward to full rear?

The time should not exceed 20 seconds for screws with a diameter of up to 2 meters and 30 seconds for screws with a diameter over two meters.

At what rotations of the thruster blades should it be launched?

Starting is carried out only at zero pitch of the adjustable pitch propeller blades, which, as a rule, are installed on thrusters.

What is cavitation?

This is the occurrence of alternating pressure on the propeller blades or in the pipeline, in which a vacuum occurs in certain areas, leading to cold boiling of the liquid (formation of air bubbles), and then, with a sharp increase in pressure, the bubbles collapse. Cavitation leads to rapid destruction of the surface of a part or component of a ship's technical equipment. facilities.

Basic units of measurement in SI.

These are kilogram, meter, second. Arbitrary values ​​come from them. For example: Joule - expresses the energy and work done by a force equal to 1N along a path of one meter, coinciding in the direction of the force.

What is temperature?

This is a quantitative measure of the degree of body heating. Its existence is a property of the real world that underlies the zero law of thermodynamics; if the degrees of heating of two bodies do not change when they are brought into contact with a third body, then the degrees of heating of these two bodies do not change when they are brought into contact with each other.

What is density?

Body density is the ratio of body mass “M” to its volume “V”. Dimension kg/cu. meter.

What is viscosity?

This is the property of a liquid to resist the relative movement (shear) of its particles, which causes the appearance of a force of internal friction between the layers of the liquid if the latter have different speeds of movement.

The dynamic viscosity coefficient  is a quantitative measure of viscosity and depends on the type of liquid, its temperature and pressure.

Kinematic viscosity coefficient  = \, where  is the density of the liquid.

What is the enthalpy of a body?

Enthalpy (heat content) is a function of quantities that determine the state of the body. It is the sum of internal energy and external work. Dimension kJ\kg.

The vessel is a complex engineering structure designed to move through water with various cargoes. Like any transport structure, it is characterized by a number of operational qualities: lifting capacity, cargo capacity, autonomy, reliability, etc. Since the vessel is also a floating structure, it is also characterized by seaworthiness - buoyancy, stability, unsinkability, propulsion, pitching and controllability.

vessel performance

lifting capacity

Load capacity name the weight of various types of cargo that a ship can transport. A distinction is made between net tonnage and deadweight.

Net load capacity- this is the total weight of the payload carried by the ship, i.e. the weight of the cargo in the holds and the weight of passengers with luggage and fresh water and provisions intended for them, the weight of caught fish, etc., when loading the ship according to the design draft.

Deadweight- sometimes called the total load capacity, and represents the total weight of the payload carried by the ship, constituting the net load capacity, as well as the weight of fuel reserves, boiler water, oil, crew with luggage, supplies of provisions and fresh water for the crew - also when the ship is loaded according to the design draft. If a cargo vessel takes on liquid ballast, the weight of this ballast is included in the vessel's deadweight. The deadweight value for each ship is constant and is determined by the total weight of variable cargo that can be accepted on the ship when loading it according to the design draft. In contrast to deadweight, the light weight of a ship or light displacement is the sum of all permanent weights that make up the weight of the structure of the constructed ship (the weight of the hull, mechanisms, ship devices, systems and equipment), and the weight of permanent inventory equipment. This also includes the weight of those parts of the fuel, water and oil reserves that are located in the boilers, mechanisms and pipelines of the ship's mechanical installation prepared for launch, as well as the weight of those remains of various liquid cargoes and tanks that cannot be removed during pumping.

cargo capacity

Cargo holds and other spaces intended to accommodate cargo are characterized by volume. The total volume of all cargo spaces is called cargo capacity vessel, which is measured in cubic meters.

register capacity

Cargo capacity holds just like the carrying capacity of the vessel, it does not give a complete idea of ​​its size. Therefore, for a uniform assessment and, first of all, the size of its premises, the concept of registered capacity, or registered tonnage, has been adopted in world practice. In this case, a registered ton equal to 2.83 cubic meters is taken as a unit of volume. m (or 100 cubic feet). The registered ton, which is a measure of volume, should not be confused with the ordinary ton, which is a measure of weight.. There are different gross tonnage of a ship - gross and net capacity - net.

travel speed

Travel speed is the most important operational quality of a vessel, determining the speed of transport operations. For river boats, speed is measured in knots, for river boats - in kilometers per hour.

cruising range

Cruising range call the distance that ship or vessel can pass at a given speed without replenishing fuel, boiler feed water and oil. The cruising range is determined by the purpose of the vessel.

autonomy

Autonomy called the length of stay ship or vessel on a flight without replenishment of fuel, provisions and fresh water necessary for the life and normal activities of people on board (and passengers).

seaworthiness of the vessel

buoyancy

Buoyancy called the ability of a vessel to float in a certain position relative to the surface of the water for a given number of people in it.

stability

Stability is the ability of a vessel, brought out of an equilibrium position by the action of external forces, to return to a state of equilibrium after the action of these forces ceases.

unsinkability

Unsinkability of the ship they call its ability, after flooding part of the premises (for example, when) to remain afloat and maintain stability and a certain reserve of buoyancy.

speed of the vessel

Speed ​​of the vessel is called its ability to move through water at a given speed, under the influence of a driving force applied to it. A distinction is made between the speed of the vessel during testing and the operational speed, i.e. the speed in the operating mode of the power plant.

pitching

Pitching are called oscillatory movements near the equilibrium position performed by a vessel freely floating on the surface of the water.

controllability

Vessel controllability characterized by two qualities: agility, i.e. the ability of the vessel to change the direction of movement at the request of the navigator, and stability on course, i.e. the ability of the vessel to maintain the straight direction given to it without deviating to the sides. Unstable on course ships are called prowling.

diagram of the general layout and structure of a dry cargo ship

1 - upper deck; 2 - bulwark; 3 - cargo boom; 4 - ventilation head; 5 - cargo winch; 6 - cargo mast (column); 7 - recovery boiler; 8 - radar antenna; 9 - wheelhouse; 10 - railing; 11 - ventilation deflector; 12 - cargo hatch coaming; 13 - cargo hatch closure covers (open hatch); 14 - foremast; 15 - saling platform; 16 - hatch cover; 17 - mooring hawse; 18 - mooring bollards; 19 - windlass; 20 - visor; 21 - anchor chain stoppers; 22 - ; 23 - forepeak; 24 - forepeak (collision) bulkhead; 25 - pillers; 26 - transverse waterproof bulkhead (corrugated); 27 - second bottom flooring; 28 - second (lower) deck; 29 - bottom stringer; 30 - flor; 31 - deck set; 32 - cargo twin-deck; 33 - cargo hold; 34 - zygomatic keel; 35 - engine room; 36 - diesel generators; 37 - main engine; 38 - thrust bearing; 39 - propeller shaft corridor; 40 - shafting; 41 - propeller (); 42 - steering wheel; 43 - tiller compartment; 44 - steering gear;

Methodology for determining the weight of cargo on board a ship using the draft survey method

After the vessel has received free practice, a surveyor arrives on board to conduct a draft survey.

The purpose of a draft survey is to determine the weight of cargo on board a vessel. By measuring the draft, using the ship's cargo documentation and information on calculating the loaded volume of the ship, using the density of the water in which the ship is located, the surveyor can calculate the weight of the ship. From this total he subtracts the weight of the vessel and other weights on board the vessel which are not the weight of the cargo, the difference being the weight of the cargo (see attached forms 1, 2, 3, 4). However, in practice, it must be taken into account that the ship is flexible and is not at rest; the ship builders’ information about the ship varies. It is very difficult to accurately measure precipitation and find out the actual weight of ballast.

The time it takes to conduct a draft survey will depend on many factors: the size of the vessel, the amount of ballast, the number of tanks, and the condition of the vessel. It is common practice for a surveyor to be present from the beginning to the end of cargo operations. On large ships, two surveyors are required to carry out a draft survey.

The accuracy of measurements during a draft survey is affected by the situation on the vessel and time constraints. Minor errors will not cause significant damage if the vessel is small in size. However, when transporting large quantities of valuable cargo, 1% of the weight of this cargo represents a large amount of money. The surveyor must demonstrate that he has made every effort to take the most accurate measurements possible using standard methods. The surveyor must be confident in what he is doing and be able, as far as possible, to prove that he is right.

1.0. Determination of cargo mass based on the vessel's draft.

1.1. Removing the vessel's draft.

The draft of the vessel (T) is the depth to which the hull of the vessel is immersed in water. To measure the draft values ​​on the bow and stern perpendiculars (stem and stern, respectively), recess marks are applied on both sides. Marks of recesses are also applied on both sides in the middle (midship) of the vessel to remove sediments in the midships.

Recess marks may be indicated by Arabic numerals and presented in metric measurement (meters, centimeters - Appendix 1), as well as Arabic or Roman numerals - English measurement system (feet, inches - Appendix 2).

With the metric draft measurement system, the height of each digit is 10.0 cm, the vertical distance between the digits is also 10.0 cm, the thickness of the digits on sea vessels is 2.0 cm, on river vessels 1.5 cm. With the English draft measurement system, the height of each The digits are 1/2 foot (6 inches), the vertical distance between the digits is also 1/2 foot, and the thickness of the digits is 1” (inch).

The line of contact of the ship's hull with water (the actual waterline) at the intersection of the recess marks in the bow of the ship gives the bow draft (Tn), in the middle of the ship - the midsection draft (Tm), in the stern - the stern draft (Tk).

Sediment removal is carried out from both sides of the vessel with the greatest possible accuracy from the pier and/or boat.

When the sea is rough, it is necessary to determine the average amplitude of water washing each mark of the depression, which will be the actual draft of the vessel in a given place (Fig. 1.):

The actual draft (Fig. 1) is: (22’07” + 20’06”) / 2 = 21’06.5”. If it is impossible to remove the draft from both sides, the draft is removed from the recess marks in the bow, amidships and aft on one side.

For the obtained settlement values, the average settlement is calculated (formula 1) :

Where T'- average draft, m;

T - draft taken in the bow, stern and amidships, m;

B - transverse distance between the recess marks of the right and left sides, m;

q is the angle of roll (read from the inclinometer located on the navigation bridge of the vessel) of the sides of the vessel with the maximum possible accuracy from the berth, °

(1° of heel is approximately equal to the width of the vessel).

The sign of the correction is negative if the roll is towards the observed side, and positive if the roll is in the opposite direction . The calculation of the average draft in the bow, stern and amidships is carried out separately.

The amidships draft can be determined by measuring the freeboard from the main deck line to the water table, which is then subtracted from the height from the keel to the main deck (Fig. 2.):

Determination of draft amidships

Designations for Fig. 2. :

1 - main deck line;

2 - waterline;

3 - freeboard height to waterline;

4 - draft to the waterline;

5 - draft to summer load line;

6 - summer freeboard;

7 (H) - height from the keel to the main deck;

8 - keel line.

1. 2. Determination of the average of the average calculated draft, taking into account corrections to the draft in the bow and stern parts of the vessel, as well as the trim and deformation of the vessel.

Measurements of draft in the bow of the vessel are recorded according to the marks of the recesses marked on the stem, and not along the bow perpendicular, which is the design line. As a result, an error appears, which is eliminated by introducing a correction (see Fig. 3., formula 5):

Introduction of amendments to draft in the bow and stern of the vessel and amidships

f - distance from the stem to the bow perpendicular, m;

LBM = LBP – (f + a) - trim - the difference in draft of the vessel in the bow and stern, m;

LBP - the distance between the perpendiculars passing through the intersection points of the load waterline with the leading edge of the stem and the axis of the rudder stock (the distance between the bow and stern perpendiculars), m.

When trimming the vessel, measurements of the draft of the stern part of the vessel are recorded according to the marks of the recesses on the stern post, and not along the stern perpendicular; therefore, the same correction must be introduced for the draft taken in the stern part (formula 6):

a - distance from the recess marks to the stern perpendicular, m.

Distances A And f can be determined using a scale drawing of the ship or a longitudinal section of the ship.

In most cases, modern ships have tables or graphs of the dependence of the magnitude of corrections on trim.

The drafts of the bow and stern parts of the vessel, taking into account corrections for the deflection of the stems, are calculated according to formulas 7, 8:

The average draft between the bow and stern of the vessel is determined by formula 9:

A correction to the midship draft is introduced if, when removing the midship draft, the deepening scale is shifted to the bow or stern of the vessel from the plimsol circle (formula 10):

Where diff.'- trim determined after introducing amendments to the drafts of the bow and stern parts of the vessel;

m is the distance from the plimsol circle to the midship recess mark, m.

The sign of the correction is negative when the mark of the recesses is shifted towards the stern and positive when the mark of the recesses is shifted towards the bow from the plimsol circle.

Precipitation at midships, taking into account the correction, is calculated using formula 11:

The average settlement is calculated using formula 12:

The average of the average calculated draft, taking into account the deformation of the vessel (bending-deflection), is determined by formula 13, 14, 14 A:

1. 3. Determination of the vessel's displacement.

Weight displacement is the mass of a vessel equal to the mass of water displaced by the vessel. Since the displacement of a vessel varies depending on the degree of its loading, any value of draft (deepening of the vessel's hull into the water) corresponds to a certain displacement.

The total carrying capacity of the vessel is deadweight – is determined as follows (formula 15, 16):

If we take the mass of the ship's stores and the mass of the “dead” cargo unchanged, then the mass of the cargo will be equal to the difference between the deadweight of the vessel with cargo (DWTg) and the deadweight of the vessel before loading / after unloading (DWT0). The quantity of cargo determined in this way must be clarified taking into account changes in the mass of ship supplies during cargo operations.

Part ship's stores includes:

• mass of fuel and lubricating oils;
• mass of drinking and technical fresh water;
• the mass of ship supplies of provisions and supplies (paint, spare parts, etc.);
• weight of the ship's crew with luggage at the rate of 1 ton of luggage for 12 people.

Part dead weight includes the mass of unpumped ballast, remaining water in tanks, etc.

The vessel's displacement is determined by load scale(Appendix 3), which is a drawing table consisting of a number of scales with divisions:

• deadweight scale, t;
• displacement scale, t;
• draft scale, m and/or feet;
• trim moment scale, tm/cm;
• the tons per cm draft scale shows, for a particular draft, the amount of cargo that must be removed or loaded to change the ship's draft by 1 cm (can be expressed in tons per inch);
• freeboard scale, m and/or feet.

When using a load scale, the values ​​of displacement and deadweight must be determined using the fresh water scale (g = 1.000) if the ship is in fresh water, and using the sea water scale (g = 1.025) if the ship is in sea water. The value of the number of tons per 1 cm of draft should be taken from the load scale only in the area of ​​the found average draft.

Displacement (D) determined before and after loading (unloading) of the vessel by the average average design draft on the load scale, hydrostatic table (Appendix 4) or hydrostatic curve (Appendix 5). Typically, displacement is indicated for sea water (r = 1.025 t/m3).

1. 4. Corrections for ship trim.

Cargo hydrostatic tables or hydrostatic curves, which give displacement at different drafts, are calculated for a vessel on an even keel. The true displacement of a vessel trimmed to the stern or bow differs from the displacement given in the load scale or table, therefore, must be applied trim corrections(formulas 18, 19 - if calculations are carried out in the metric system; formulas 20, 21 - if calculations are carried out in the English system):

To do this, you must first add 50 cm (6 inches) to the draft value and remove the value from the hydrostatic tables of the trimming moment, and then subtract 50 cm (6 inches) from it and use this data to determine the value of the trimming moments. The difference between the trimming moments will be this value.

The sign of the first amendment is obtained algebraically (Table 1):

The sign of the second amendment is positive. The general correction for trim is expressed by formula 22:

Displacement corrected for trim is determined according to formula 23:

1. 5. Correction for seawater density.

In cases where the actual density of water differs from the accepted one (r = 1.025 t/m3), it is necessary to introduce a correction for the density measured by a hydrometer, hydrometer, or accepted according to the port weather service data to the displacement corrected for trim.

Seawater samples to determine actual density should be taken at a depth corresponding to approximately half the vessel's draft and approximately halfway through the vessel. To obtain more accurate data, samples can also be taken near the bow and stern of the vessel.

If an ariometer (hydrometer) calibrated at a temperature of 15°C is used to determine the density of water, then the actual density is determined using the following table 2 based on measured density and actual water temperature.

The correction for water density is determined by formula 24, 24 A:

The displacement, taking into account the correction for the density of sea water, is determined by formula 25:

2.0. Determination of the mass of ship's stores.

Before and after loading (unloading) the vessel, it is necessary to determine the amount of variable stores that must be deducted from the displacement as not related to the payload.

TO variable ship supplies relate:

• fuel (diesel, fuel oil);
• lubricating oil;
• fresh water (drinking, technical);
• ballast water.

To determine the mass of variable reserves, immediately after the vessel's draft is removed, all ship's tanks should be checked.

Determination of the amount of fresh water and ballast.

On a ship, fresh water can be stored in galley and sanitary tanks, in forepeak and afterpeak tanks, in deep tanks and bottom tanks (boiler water).

The bottom part of the vessel consists of a double bottom, which houses double-bottom tanks intended for ballast. Double-bottom tanks run either across the entire width of the vessel or are divided along the axis of the vessel into two symmetrical tanks. Often, double-bottom tanks are separated from each other by special tanks that serve to ensure the safety of the vessel in case of a hole.

The water level in tanks is measured using measuring tape (roulette) through measuring tubes. After determining the water level by calibration tables available on the ship, the amount of water in tons or cubic meters is determined. If the amount of water is given in units of volume, then it is converted to tons by multiplying the volume by the density at a given temperature. Measuring the amount of water at a significant trim requires introducing a trim correction using calibration tables or calculating the trim correction using the “wedge” calculation method. (Appendix 6).

Water on the ship can also be found in bilges (ship drainage reservoirs) located along the sides. Sewage tanks must be emptied before measuring sludge.

Determination of the amount of fuel and lubricating oils.

Fuel (diesel, fuel oil) is located in bottom, service and settling tanks, as well as in deep tanks. There are small lubricating oil tanks in the engine room. Responsibility for measuring the amount of fuel and lubricating oil lies with the chief engineer, who has calibration tables compiled in tons or cubic meters. Data from measurements and calculations of all reserves are summarized in table 3, 3a.

3.0. Time required to conduct a draft survey.

To conduct a draft survey on a small standard vessel and obtain effective results, a qualified surveyor will need about half an hour. If this is a large vessel carrying bulk cargo and arriving in ballast, it will take at least four hours to process it with the participation of at least two surveyors. Most vessels are average in size and can be placed between the two examples above. Much also depends on the type of vessel and the crew involved.

There is a huge difference in the time and effort required to conduct the initial, final draft survey and determine the weight of the cargo. During the initial and final draft survey (before and after loading), all variables are measured - precipitation, variable ship supplies (ballast and fresh water, fuel, lubricants, etc.). It is believed that this method helps eliminate errors that could arise when determining the light weight of the ship and the weight of the ship's stores, and gives a more accurate result. Measurements of ballast tanks and sediment removal are carried out upon the vessel's arrival at the port and upon completion of loading.

A simpler method is a deadweight survey. It includes measurements of draft and variables only when the ship is already fully loaded. It is used if the ship constantly transports a certain type of cargo along a certain route, all its variables are known and the ship constant (constant) is accurately calculated. This method has some other benefits besides saving time. Since measurements are taken with the ship loaded, it is possible to avoid deviations that occur when measurements are taken on a ship with a large trim.

4.0. Accuracy of measurements.

An experienced surveyor, working under ideal conditions, will measure to within ±0.1 - 0.3% on a large vessel and to within ±0.4 - 0.7% on a small vessel. If you look at things realistically, it is almost impossible to provide ideal working conditions. Therefore, measurements are carried out with an accuracy of 0.5% of the total mass of the cargo.

If the instruments used to take measurements are of insufficient quality, the measurement accuracy will fluctuate within 1%. Technical errors may go unnoticed by the surveyor, and even more so by his employer, who has no idea about the operating principle of this method. Even with the best technology, adverse weather conditions and lack of crew assistance can affect the measurement accuracy by up to 0.5%. Since the measurements taken represent only initial information, inaccurate measurements will lead to errors in further calculations. Disagreements in the work of the surveyor and the crew, its inconsistency will also affect the flow of the draft survey, such as:

• crew recalculation of ballast and fuel mass during survey;
• blocking of measuring tubes;
• changing documents;
• creating other obstacles to the normal work of the surveyor.

It would seem that such insignificant things that happen during the removal of draft, such as the opening or closing of holds, vibrations caused by the movement of cranes, can lead to a significant change in trim and draft.

The surveyor's only defense is attention to the smallest details, as well as the dexterity acquired along with sea experience. A detailed study of the ship's plans also often reveals inaccuracies and errors, but since not every plan can exactly correspond to a given ship, any conclusions must be drawn on this basis very carefully.

5.0. Draft.

The first step of a draft survey is to remove sediment. The draft will be measured in the bow, stern and amidships on both sides of the vessel (six values). The surveyor should be as close to the water as possible to obtain more accurate draft readings. When handling large vessels, it is mandatory to use a boat to remove sediment from the sea side. An attempt to measure the draft of a large bulk carrier in ballast from a ladder can lead to an error of up to 100 tons.

It is important to pay attention to the clarity of load lines. On some seagoing vessels, load lines are marked in Arabic numerals (metric) on one side and Roman numerals (English feet) on the other. In this case, upon completion of sediment removal, all readings should be transferred to one system.

Water fluctuations make it difficult to remove sediment. Special measuring tubes are used. Water passes inside a narrow glass tube and, having reached a certain level, stops. Then readings are taken on the load scale.

Another way to remove sediment from the sea side is to measure the ship's roll (if any) with a special device - an inclinometer. Next, precipitation is calculated using simple trigonometry. However, accurate inclinometers are very rare, so this method is applicable only in conjunction with another for further comparison of the obtained indicators.

The draft survey report must contain a description of the weather conditions during the survey. In urgent cases, it is better to postpone the survey due to bad weather conditions.

Currents and shallow water also make it difficult to remove sediment, significantly changing its values. If the ship moves relative to the water, especially if there is a small under-keel clearance (the distance between the ship's hull and the ground), it will sink more into the water, increasing the draft as a result of the “suction effect” and changing the trim. It has been experimentally established that the influence of current speeds up to four knots on changes in draft and trim is insignificant. If the current speed is four knots or more, the draft can increase to 6 cm, depending on the shape of the vessel.

Current is a real problem for river moorings. The theoretical and practical work carried out to calculate the “suction effect” is insufficient. Therefore, the surveyor's only choice is to rely on his professional experience.

In bright sunshine and low water temperatures, there is a tendency for ships to bend their hulls. The deck expands, but the bottom of the ship does not, which leads to a bowing of the ship's hull. The way out of this situation is to use special adjustment methods to help avoid errors in calculations.

6.0. Density.

The next step of the draft survey after removing sediments is to measure the density of the water in which the vessel is located. It is important to measure the density of water immediately after removing sediment, since it can change with the tide, as well as with changes in water temperature. The very concept of “density” is often misunderstood - we are talking about the ratio of mass and volume.

All errors in determining the density of water are the result of insufficient practice and misunderstanding of the relationships between different densities. Typical errors are as follows:

• improper water sampling;
• neglect to use corrections for water temperature;
• the use of special indicators of gravity (density) in a vacuum instead of using mass indicators in air.

The best option for determining water density is to take samples three times at different depths in the bow, stern and amidships (9 values). The number of samples may be smaller if the vessel is small or if experience shows that for a given berth the water density is constant at a certain depth. In total, at least a liter of water samples should be taken. The water is then placed in a special transparent vessel for testing. This must be done immediately while the seawater temperature remains constant.

There is no need to measure the water temperature when using a glass hydrometer. It is important to determine the water density values ​​at the time of the draft survey. Applying corrections to density measured with a hydrometer leads to distortion of the obtained values. As the temperature changes, the ship's hull will expand and contract, and the same changes will occur with the hydrometer - therefore, there is no need to introduce corrections to the density.

The surveyor must ensure that the base of the hydrometer and the surface of the water are not contaminated with oil or grease. Then lower the device into the water and record the value of the intersection of the water level and the device scale. It is important that your eyes are opposite the device and not at an angle. The hydrometer must be designed specifically for seawater.

Density values ​​will be in the range of 0.993 - 1.035 t/m3. To take measurements, you need a hydrometer capable of measuring mass in air (apparent density), mass in vacuum (actual density) and a special indicator of gravity (relative density). The surveyor will need to determine the weight of the cargo in air as this is the generally accepted commercial weight. Therefore, in his calculations he must use the apparent density or mass per unit volume in air.

The units of measurement are usually kg/l. If the hydrometer is intended to measure mass in a vacuum or take the gravity indicator, a correction of 0.0011 gm/ml is applied; it must be subtracted from the resulting density value to obtain the mass in air.

To summarize, we highlight the main thing for a surveyor when determining the density of water:

• take the required number of samples;
• use an accurate hydrometer;
• do not apply temperature corrections;
• determine the mass of a unit volume in air, kg/l.

7.0. Masses to be determined.

Once the values ​​of draft and water density have been determined, the values ​​of all masses are established, which will then need to be subtracted from the displacement to determine the mass of the cargo. The light weight of the ship, the amount of ballast, ship stores, as well as the value of the ship constant or ship constant are determined. On a small ship, one surveyor can handle this task. If this is a very large ship awaiting loading or preparing to leave for a voyage, the surveyor will need an assistant. While the first will determine the values ​​of draft and water density, the second will be engaged in measuring ship tanks.

Light weight of the vessel.

The light weight of the ship is taken on faith based on the ship's information. If the same erroneous light weight value was used during the initial and final draft surveys, this will not result in an error. If one value was used in the initial draft survey, and another in the final one, this will lead to an error. When conducting a deadweight survey, any error in determining the light weight of the vessel will lead to an erroneous value for the cargo weight.

Ballast.

Determining the amount of ballast represents the largest amount of work. The surveyor must measure all ballast tanks and determine the amount of ballast in them. To do this, it is best to use a steel tape measure with water marking paste.

It is ideal for the ship to have no list and be on an even keel, but in practice this is almost impossible to achieve. The roll can be corrected by moving ballast from one tank to another. However, this operation will be time-consuming and may result in problems associated with pumping ballast during the survey, which will affect its accuracy. Introducing a heel correction for each ballast tank is also a labor-intensive operation, which is not required if the heel is small.

A ship in ballast always has a large trim to the stern. Some ships are equipped with appropriate tables for adjusting trim when performing calculations in ballast tanks, some are not. To avoid calculating trim corrections, many surveyors insist that ballast tanks be either empty or full during the survey. The surveyor, having made sure that some of the ballast tanks are filled, takes measurements of the remaining empty tanks. This procedure will not take much time; it is acceptable for small tank ships that do not have too much trim.

Measurements made in full ballast tanks on a heavily trimmed vessel will be a source of error. Measurements in empty tanks will be more accurate, but there remains the possibility of residual ballast water in the tanks, the amount of which cannot be determined.

Measuring ballast holds is a complex operation and is also a source of possible errors. The hold must be empty and dry before the initial draft survey is carried out. If this is not possible, the surveyor should measure the voids in different parts of the hold to obtain the correct depth value to enter into the calibration tables.

Having carried out the necessary measurements and received the values ​​of the depth of water in the tanks, the surveyor, using calibration tables or by calculations, converts these values ​​into m. Knowing the density of water in each tank, which he also had to determine, the surveyor sets the amount of water in the tanks. However, it is difficult to determine the density of water in the ballast tank, and it is not enough to believe the statements of the chief mate that the ballast was taken on board on the high seas. An error in the value of ballast water density for large ships can lead to a change in cargo weight of up to 150 tons or more.

Thus, the surveyor must, by any available means, take samples of water from all or several of the ballast tanks and determine its density using the same hydrometer with which he measured the density of sea water.

To summarize, we highlight the main thing for a surveyor who determines the amount of ballast on board a ship:

• carefully read the plans for the location of ballast tanks;
• take measurements of ballast tanks using a steel tape measure with water marking paste;
• determine the density of water in each tank;
• calculate the volume occupied by water in each tank, applying the necessary corrections for heel and trim;
• determine the amount of ballast water in each tank using the product of volume and density.

Fresh water.

The amount of fresh water is determined similarly to the amount of ballast. It is less labor intensive, there are fewer fresh water tanks, and there is usually no need to determine the density of the water.

Heavy and diesel fuel, lubricating oils.

If the ship did not take fuel on board during its stay in the port, the surveyor uses in the calculations the amount of fuel and lubricating oils specified in the fuel quality certificate (Bunker Receipt - see. table 3). If the vessel took on fuel between the initial and final draft survey or if a deadweight survey is being carried out, the surveyor must measure the fuel tanks and determine the amount of fuel and lubricating oils by calculation. Calculations and adjustments for roll and trim are made as for ballast tanks. For fuels and lubricating oils, density values ​​at 15°C are typically used. To measure fuel tanks, it would be more advisable to use a special hydrometer for fuel, which determines the exact density value. However, such hydrometers are not used because the amount of fuel and oil is not large and the possibility of error is also very small. It must be remembered that cooled fuel or oil moves very slowly, so if there is a change in trim, it may be time to determine the exact depth of the liquid in the tank. In this case, measuring voids in the tank will give a more accurate result.

Reserves and ship constant.

The ship's constant, contrary to its name, is not a constant value. It represents the difference between the net displacement and the value of all the ship's variable reserves (ballast, fresh water, fuel and lubricants, slop water, etc.).

The constant includes crew supplies, paint, remaining dirt in tanks, minor discrepancies in load line marks, and inaccuracy in determining the ship's light weight.

During the initial draft survey, carried out on a ship in ballast, the surveyor determines the constant by calculation. For a small bulk carrier, the normal value of the constant is about 250 tons. Older ships have a higher constant than newer ships. The value of the constant will fluctuate with changes in the amount of fastening materials and supplies on board, as well as with the appearance of ice and snow on the deck. Due to these factors, which cannot be determined by calculation, the light weight of the vessel can change by 60 tons.

In some cases the surveyor receives a negative constant. This is usually a sign of an error. However, if after repeated measurements and calculations the constant remains negative, this value should be used.

A negative constant can result for the following reasons:

• Offset of the weight scale.
• Some vessels use ballast tank calibration charts and hull data developed for another vessel of the same type. Vessels of the same type differ slightly from each other, but the same tables are used.
• On some ships, the cause of significant errors is trim that is much greater than permissible. Such vessels are a kind of scourge for draft surveyors. If the chief officer is unable to provide constant values ​​from previous voyages in the event of a theoretically unacceptable result, the accuracy of the results of this draft survey will be questionable.

When conducting a deadweight survey, the surveyor either determines the value of the ship's constant approximately or takes its value on faith based on the vessel's information. The deviation of the constant from its actual value means the same deviation of the amount of cargo from its actual amount on board.

A deadweight survey is often more accurate than a full draft survey, since it is possible to avoid the mistakes of the initial draft survey associated with the large trim of the vessel. Measurements are carried out on a loaded ship, all calculations are carried out as for a ship on an even keel, which allows you to avoid many mistakes.

If the ship is regularly surveyed, it is useful to compare the values ​​of the constant over several voyages and determine the value with which the survey was most accurate.

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Meaning of the word deadweight

deadweight in the crossword dictionary

New explanatory dictionary of the Russian language, T. F. Efremova.

deadweight

m. The main characteristic of a vessel is its total carrying capacity, including the weight of cargo, people on board, as well as all fuel, water, etc., necessary for navigation.

Encyclopedic Dictionary, 1998

deadweight

DEADWEIGHT (full carrying capacity of the ship) is the mass of cargo (payload, ship supplies, crew) accepted by the ship. Deadweight at load line draft is the main operational characteristic of a sea vessel.

Deadweight

(eng. deadweight), the total weight of cargo that the ship accepts. D. at summer load line draft in sea water is an indicator of the size of a cargo ship and its main operational characteristic. Numerically, D. is equal to the difference between the displacement and the dead weight of the vessel with the mechanisms ready for action (with filled fuel pipelines, with water in boilers, cooling pipelines, etc.). The main part of the cargo ship's weight is the weight of the cargo; on a passenger ship, the weight of the cargo (passengers and luggage) constitutes a smaller part of the cargo, and the majority of it is consumable ship supplies (fuel, water).

Wikipedia

Deadweight

Deadweight- a value equal to the sum of the masses of the variable cargo of the ship, measured in tons, that is, the sum of the mass of the payload carried by the ship, the mass of fuel, oil, technical and drinking water, the mass of passengers with luggage, crew and food.

Deadweight is the difference between full displacement and empty displacement.

In commercial shipping, a distinction is made between the net deadweight capacity (abbreviated as DWCC) and the deadweight or gross deadweight of the vessel.

The first is the maximum mass of cargo that the ship can take up to the maximum load line draft. This value may vary depending on the actual load of the ship with fuel and supplies.

The total or gross deadweight is a constant and includes, in addition to the total weight of the cargo, also the total weight of the crew members, removable equipment and ship stores

The term "deadweight" is used only for merchant ships, and for purely cargo ships. Deadweight at load line draft is an indicator of the cargo capacity of a cargo ship and its main operational characteristic.