Method for obtaining draught of propeller blades

Abstract

According to the method, a bow draught measuring sensor is arranged at the bow part of a ship, a stern draught measuring sensor is arranged at the stern part of the ship, when the longitudinal inclination of the ship is in a stern inclination state, the distance from a propeller blade to the stern draught sensor is defined as L1, the distance from a stern water gauge mark to the bow draught sensor is defined as L2, and the L1 is a positive integer; and by analyzing the relationship among the parameters, establishing a model to obtain the draft Tp at the propeller blade. When Tplt; and when the upper edge of the propeller blade is high, the propeller is not completely immersed. In practical engineering application, the calculation can be completed by a central control system, a cabin monitoring alarm system or a liquid level telemetering system, and an alarm is extended to a control center to remind sailors that the propeller is not completely immersed, so that the rotating speed of a main engine is reduced or the longitudinal trim of a ship is adjusted, and the high temperature of a stern tube bearing is avoided.

Description

Technical Field

[0001] The present invention belongs to the field of marine ship design and construction, and particularly relates to a method for obtaining the draft of a propeller blade. Background Art

[0002] When a ship is sailing normally, the propeller rotates in the water to push the water backward, and at the same time the water generates a forward reaction force on the propeller, so that the ship moves forward. This thrust is centered on the propeller center, symmetrically balanced, and its resultant force has no other effect on the shafting except for the thrust. However, when the ship is in ballast or light load, some propeller blades may be exposed above the water surface, lacking the reaction force of the water. The reaction force of the water acts on the lower part of the propeller, and this force cannot be symmetrically balanced, thus generating a bending moment on the shafting, causing the lower part of the stern bearing to bear an additional increased load. When the wedge-shaped oil film formed by the rotation between the shaft and the bearing is not sufficient to support the shafting load, dry friction occurs between the shaft and the bearing, resulting in high temperature or even melting of the stern tube bearing. Therefore, ensuring that the propeller blades are completely immersed in water can, to a certain extent, avoid high temperature or melting of the stern tube bearing.

[0003] Due to different loading conditions of the ship, the longitudinal inclination of the ship will also be different. In actual work, the actual draft of the ship is usually obtained by observing the ship's water level gauge, with a large error and high labor cost. The draft at the propeller blade is usually only based on experience or visual estimation. Summary of the Invention

[0004] To solve the above problems, the present invention provides a method for obtaining the draft of a propeller blade, and the technical solution adopted is as follows:

[0005] A method for obtaining the draft of a propeller blade, with a bow draft measurement sensor provided at the bow of the ship and a stern draft measurement sensor provided at the stern of the ship. Assuming the ship has no transverse inclination, the following operations are carried out:

[0006] When the ship is in a longitudinally level state, the data measured by the bow draft measurement sensor or the stern draft measurement sensor is the draft data at the upper edge of the propeller blade;

[0007] When the ship is in a stern-down state, the following definitions are made:

[0008] Ta: Draft value of the stern draft sensor, unit m;

[0009] Tf: Draft value of the bow draft sensor, unit m;

[0010] Trim: Draft difference, Trim = Ta - Tf;

[0011] Among them, the line connecting the measured draft values of Ta and Tf is the ship's draft line;

[0012] Define the distance from the propeller blade to the draft sensor at the stern as L1, with the unit of m;

[0013] Define the distance from the waterline mark at the stern to the draft sensor at the bow as L2, with the unit of m;

[0014] Establish a model by analyzing the relationships among the above parameters;

[0015] Then the draft Tp at the propeller blade is calculated as follows:

[0016]

[0017] When Tp < the height at the upper edge of the propeller blade, it can be considered that the propeller is not fully submerged; the calculation result is sent to the control center in the form of a signal to issue an alarm, reminding the crew that the propeller is not fully submerged, and then reducing the main engine speed or adjusting the trim of the ship.

[0018] This patent utilizes the existing draft measurement data of the ship. By establishing a mathematical model of the draft at the bow and stern draft sensors, the hull waterline, and the draft at the propeller blade, the draft data at the propeller blade is calculated in real time; meanwhile, when the draft at the blade is lower than the height of the upper edge of the blade, an alarm is set to remind the ship operator, providing a solution to avoid the high temperature of the stern tube bearing. Compared with the existing passive solution of avoiding the high temperature of the bearing by monitoring the temperature of the stern tube bearing, it is more direct and forward-looking. Brief Description of the Drawings

[0019] Figure 1 It is a schematic diagram of the installation of the bow draft measurement sensor and the stern draft measurement sensor of the ship;

[0020] Figure 2 It is the mathematical model established when the ship is in a stern trim state. Detailed Description of the Invention

[0021] The present invention will be further described in conjunction with the accompanying drawings.

[0022] A method for obtaining the draft of the propeller blade. Taking a certain oil tanker as an example, according to the requirements of the SOLAS regulations, a bow draft measurement sensor is installed at the bow of the ship, and a stern draft measurement sensor is installed at the stern of the ship, as Figure 1 shown.

[0023] Since the transverse inclination of the ship has little influence on the draft at the propeller blade, therefore, the following descriptions and calculations of the present invention are all based on the assumption of no transverse inclination.

[0024] There are three attitudes of the ship's longitudinal inclination: even keel, bow trim, and stern trim. Since bow trim will seriously affect the stability, strength, and navigation speed of the ship, therefore, the ship usually maintains an even keel or stern trim state during normal navigation.

[0025] When in the upright floating state, the data of the bow and stern draft sensors will be equal. Therefore, the data measured by the bow or stern draft sensor is the draft at the upper edge of the propeller blade.

[0026] When in the stern trim state, the draft at the bow will be less than the draft at the stern, forming a draft difference. Therefore, the following definitions are made:

[0027] Ta: Draft value measured by the stern draft sensor, unit: m

[0028] Tf: Draft value measured by the bow draft sensor, unit: m

[0029] Trim: Draft difference, Trim = Ta - Tf

[0030] Among them, the line connecting the measured draft values of Ta and Tf is the ship's draft line.

[0031] Define the distance from the propeller blade to the stern draft sensor as L1, unit: m;

[0032] Define the distance from the stern water gauge mark to the bow draft sensor as L2, unit: m;

[0033] By analyzing the relationship between the above parameters, a model can be established, as Figure 2 shown. According to the triangle ratio relationship, there is:

[0034]

[0035] It is derived that:

[0036]

[0037] Then the draft Tp at the propeller blade is calculated as follows:

[0038]

[0039] For the propeller, when the propeller is completely submerged, the draft value at the upper edge of the propeller blade is greater than the height at the upper edge of the propeller blade.

[0040] Taking a certain crude oil tanker as an example, the following data can be obtained according to the actual ship draft sensor and propeller blade installation:

[0041] The distance L1 from the propeller blade to the stern draft sensor is 13.1 m.

[0042] The distance L2 from the stern draft sensor to the bow draft sensor is 144 m.

[0043] The draft at the upper edge of the blade is 10.6 m.

[0044] Suppose the data measured by the draft sensor at the stern of the actual ship is Ta = 10.4 m; the data measured by the draft sensor at the bow is Tf = 7.9 m.

[0045] Then substitute into the formula It can be seen that at this time, the upper edge of the propeller blade is just on the draft line. When the measured data is lower than this value, the incomplete immersion alarm of the propeller can be triggered. In actual projects, to avoid false alarms, a certain value can be increased on the basis of 10.6 m, for example, 200 mm can be increased to avoid false alarms caused by sea waves and measurement errors.

[0046] Therefore, when Tp

Claims

1. A method for obtaining the draft of a propeller blade, characterized in that, The bow of the ship is equipped with a bow draft measurement sensor, and the stern of the ship is equipped with a stern draft measurement sensor. Assuming that the ship has no transverse inclination, the following operations are carried out: When the ship's longitudinal inclination is in the upright state, the draft data measured by the bow draft measurement sensor or the stern draft measurement sensor is the draft data at the upper edge of the propeller blade; When the ship's longitudinal inclination is in the stern-down state, the following definitions are made: Ta: Draft value of the stern draft sensor, unit m; Tf: Draft value of the bow draft sensor, unit m; Trim: Draft difference, Trim = Ta - Tf; Among them, the line connecting the measured draft values of Ta and Tf is the ship's draft line; The distance from the propeller blade to the stern draft sensor is defined as L1, unit m; The distance from the stern water level mark to the bow draft sensor is defined as L2, unit m; By analyzing the relationships between the above parameters, a model is established; Then the draft Tp at the propeller blade is calculated as follows:

2. When Tp < the height at the upper edge of the propeller blade, it can be considered that the propeller is not fully submerged; the calculation result is sent to the control center in the form of a signal to issue an alarm, reminding the crew that the propeller is not fully submerged, and then reducing the main engine speed or adjusting the ship's longitudinal inclination.

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