A method for measuring freeboard marks of an LNG carrier

Abstract

The present application relates to a kind of for LNG ship freeboard mark measurement method, comprising selecting total station survey reference height;Selecting rib site, fill in the height measurement value and actual value of rib site, calculate average value;Practical clamp ruler measures the actual depth of freeboard mark installation position;The actual survey height of 30cm scale position to freeboard mark of 1m long steel ruler is calculated;Plate reference mark is made at the 30cm scale position of 1m long steel ruler, and survey height is measured downwards, obtains the drawing position of freeboard mark.A kind of for LNG ship freeboard mark measurement method of the present application, using special-purpose clamp ruler is inserted into the small gap between water curtain spraying device and plate rebate, the high-precision high-quality measurement of freeboard mark position is realized, and the method has wide universality.

Description

Technical Field

[0001] This invention relates to the field of ship surveying, and more specifically to a method for measuring freeboard markings on LNG carriers. Background Technology

[0002] Freeboard markings on LNG carriers are used to calculate cargo capacity during loading, directly impacting operating costs. Therefore, the positioning accuracy of these freeboard markings is crucial during shipbuilding. Accurate determination of the freeboard marking position is fundamental to precise installation; thus, measurements must first be taken on the ship's outer plating, lines drawn, and then the markings installed according to the drawn lines. The theoretical position of the freeboard marking is the height above the hull baseline. Determining this height is technically challenging, primarily because each ship's bottom inevitably has some unevenness (i.e., deflection) during construction. Therefore, the baseline height is different for each ship and must be measured on-site.

[0003] Previously, the reference height for measuring freeboard markers was determined by taking points near the ribs where the marker was installed, measuring the values ​​at several bottom points before and after the ribs, calculating the deflection, and then measuring upwards to determine the accurate position of the freeboard marker. This method has several problems: 1) The transition area from the bottom of the vessel to the side is usually designed as an arc, making it easy to introduce errors when measuring height upwards from the bottom point. Freeboard markers have an allowable error of ±1mm, requiring high precision; large errors can lead to rework and restrict production cycles. 2) Selecting several points near the ribs where the freeboard marker is installed and their surroundings as measurement points is limited, making the data susceptible to questioning during acceptance and potentially containing excessive errors. 3) When the vessel enters port after delivery, because the bottom is below the waterline, inaccurate main deck height can also lead to excessive errors in the freeboard marker measurement. Therefore, the main deck height should also be considered when measuring the freeboard marker.

[0004] Based on the above considerations, it is proposed to simultaneously measure the bottom baseline and main deck height, and then measure the height downwards from the main deck to determine the installation position of the freeboard marker. However, the installation position of the freeboard marker on the main deck of an LNG carrier differs from that of other vessels in that the water curtain spray device is installed very close to the outer plating, resulting in extremely limited measurement space on the main deck, making it difficult to measure with conventional measuring tools.

[0005] Existing technology CN207850216U discloses a template for measuring freeboard markings on large LNG carriers, including a measuring template. The left side panel of the measuring template has multiple horizontally arranged punch holes. A slot for fixing the measuring template to the hull plating is provided on the measuring template. The slot extends along the width of the measuring template and reaches its lower end. The lower end of the slot has a 45° chamfer. A fixing hole with a radius of 25mm is provided on the upper right side of the measuring template panel. This invention has a simple structure and is easy to use. By attaching the measuring template to the hull plating where freeboard positioning measurement is required, and using measuring tools to measure the freeboard markings, it not only improves the accuracy of freeboard marking measurement and reduces measurement errors, but also provides a very intuitive measurement result, improving measurement efficiency. However, this measuring template cannot be used when a water curtain spray device is installed very close to the hull plating. Summary of the Invention

[0006] To address the technical problems existing in the prior art, this invention provides a method for measuring the freeboard mark of an LNG ship. A specially designed clamp is inserted into the small gap between the water curtain spray device and the tongue and groove of the outer plate to achieve high-precision and high-quality measurement of the freeboard mark position.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A method for measuring freeboard markings on LNG carriers, the method comprising the following steps:

[0009] Step 1: Select any point on the dock pier at the bottom of the ship as the reference height for total station measurement;

[0010] Step 2: According to the whole ship bottom baseline measurement table, select the corresponding rib points on the bottom outer plate of the midship longitudinal section, place the laser measurement target, use a total station to measure the height difference between each point on the outer side of the outer plate and the reference point on the dock, and fill the height measurement value of each rib point into the whole ship bottom baseline measurement table.

[0011] The baseline measurements of the entire ship's bottom are shown in Table 1:

[0012]

[0013]

[0014] Step 3: Add the plate thickness at the corresponding rib location to the measured value in Step 2 to obtain the actual value and fill it in the whole ship bottom baseline measurement table;

[0015] Step 4: Calculate the average value of the actual values ​​at each rib point. The average value is the reference height of the bottom baseline.

[0016] Step 5: Using a clamp, transfer the height of the top of the main deck to the outside of the outer plating;

[0017] Step 6: Place the 1m long steel ruler in the clamp on the outside of the outer plate, measure the height difference between the 30cm mark of the 1m long steel ruler and the reference height of the bottom baseline, obtain the actual mold depth of the freeboard mark installation position, and record the actual mold depth.

[0018] Step 7: Subtract the theoretical height from the freeboard mark to the bottom baseline from the measured actual depth. This gives the actual survey height from the 30cm mark on the 1m long steel ruler to the freeboard mark. Step 8: Based on the actual survey height, mark the outer plating reference mark at the 30cm mark on the 1m long steel ruler, and measure the survey height downwards to obtain the position for drawing the freeboard mark.

[0019] As a preferred technical solution, in step 2, the selected rib sites cover the entire ship, and the number of rib sites is 20-30.

[0020] As a preferred technical solution, the clamp includes a 1m long steel ruler, a Teflon pad, a 30cm steel ruler, bolts, and washers. During measurement, the 1m long steel ruler is suspended on the outside of the tongue and groove joint of the outer panel, the Teflon pad is located on the tongue and groove joint of the outer panel, and the 30cm steel ruler is placed on the inside of the tongue and groove joint of the outer panel. The 1m long steel ruler, the Teflon pad, and the 30cm steel ruler are all provided with screw holes that match the bolts. The 1m long steel ruler, the Teflon pad, and the 30cm steel ruler are fixedly connected by bolts that pass through the screw holes and washers.

[0021] As a preferred technical solution, the thickness of the 30cm steel ruler should not exceed 0.5mm.

[0022] As a preferred technical solution, the graduations of the 1m steel ruler and the 30cm steel ruler are aligned.

[0023] As a preferred technical solution, the Teflon pad is installed 100mm from the bottom of the 30cm steel ruler.

[0024] As a preferred technical solution, the thickness of the Teflon pad is 25-30mm.

[0025] As a preferred technical solution, in step 6, if the measured main deck depth is found to be excessive, the main deck should be measured in advance or pyrotechnic correction and replacement of the deck should be carried out.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] (1) The present invention provides a method for measuring freeboard marks on LNG ships. By increasing the number of measurement points, the accuracy of the data is improved. The method of measuring downwards from the main deck can make up for the gap in the measurement of the ship's depth at the installation position of the freeboard mark. Thus, the position of the freeboard mark is calibrated bidirectionally with two data points: the bottom baseline and the height of the main deck, ensuring the reliability of the ship after delivery. The measurement route from the main deck to the freeboard mark is in the straight area of ​​the ship's outer plating and is not shaped, which can avoid the problem of inaccurate measurement caused by the ship's shape.

[0028] (2) The method for measuring the freeboard mark of LNG ships in this invention uses a specially made clamp, which solves the problem that the water curtain spray device is installed close to the outer plate and the measurement space is small, and ensures the general direction of the pre-installation and forward movement of the water curtain spray outfitting components.

[0029] (3) The method for measuring the freeboard markings of LNG ships of the present invention is adapted to the market demand for modern precision shipbuilding and high-quality shipbuilding, and has wide applicability. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of a method for measuring the freeboard markings of LNG ships according to the present invention, using a clamp for measurement.

[0031] In the diagram: 1. Outer panel; 2. Water curtain spray system; 3. Main deck; 41. 1m long steel ruler; 42. Teflon pad; 43. 30cm steel ruler; 44. Bolt; 45. Gasket. Detailed Implementation

[0032] The technical solution of the present invention will be further described below with reference to specific embodiments:

[0033] like Figure 1 As shown, a method for measuring freeboard markings on LNG carriers includes the following steps:

[0034] Step 1: Select any point on the dock pier at the bottom of the ship as the reference height for total station measurement;

[0035] Step 2: According to the whole ship bottom baseline measurement table, select the corresponding rib points on the bottom outer plate 1 of the midship longitudinal section, place the laser measurement target, use a total station to measure the height difference between each point on the outer side of the outer plate 1 and the reference point on the dock, and fill the height measurement value of each rib point into the whole ship bottom baseline measurement table.

[0036] Step 3: Add the plate thickness at the corresponding rib location to the measured value in Step 2 to obtain the actual value and fill it in the whole ship bottom baseline measurement table;

[0037] Step 4: Calculate the average value of the actual values ​​at each rib point. The average value is the reference height of the bottom baseline.

[0038] Step 5: Using a clamp, transfer the height of the upper opening of the main deck 3 to the outside of the outer plate 1 so that the total station can be used for measurement, avoiding the problem of tongue and groove obstruction;

[0039] Step 6: Place the 1m long steel ruler 41 in the clamp on the outside of the outer plate 1, measure the height difference between the 30cm mark position of the 1m long steel ruler 41 and the reference height of the bottom baseline, obtain the actual mold depth of the freeboard mark installation position, and record the actual mold depth.

[0040] Step 7: Subtract the theoretical height from the freeboard mark to the bottom baseline from the actual measured depth. This gives the actual survey height from the 30cm mark on a 1m long steel ruler 41 to the freeboard mark.

[0041] Step 8: Based on the actual survey height, mark the outer plate 1 reference mark at the 30cm mark position on the 1m long steel ruler 41, measure the survey height downwards, and obtain the drawing position of the freeboard mark.

[0042] In step 2, the selected rib sites cover the entire ship, with 20-30 rib sites selected. Increasing the number of selected rib sites improves the accuracy of the calculation results.

[0043] like Figure 1 As shown, the measuring tape includes a 1m long steel ruler 41, a Teflon pad 42, a 30cm steel ruler 43, a bolt 44, and a washer 45. During measurement, the 1m long steel ruler 41 is suspended on the outside of the tongue and groove of the outer plate 1, the Teflon pad 42 is located on the tongue and groove of the outer plate 1, and the 30cm steel ruler 43 is placed on the inside of the tongue and groove of the outer plate 1. The 1m long steel ruler 41, the Teflon pad 42, and the 30cm steel ruler 43 are all provided with screw holes that match the bolt 44. The washer 45 is located on the outside of the 1m long steel ruler 41 and the 30cm steel ruler 43. The 1m long steel ruler 41, the Teflon pad 42, and the 30cm steel ruler 43 are fixedly connected by bolts 44 that pass through the screw holes and the washer 45. After the clamp is in place, the actual height of the tongue and groove joint is the height from the bottom of the main deck 3 to the bottom of the Teflon pad 42 (30cm minus the height of the Teflon pad 42 on the side of the 30cm clamp). Based on this height, measure the same value downwards from the bottom of the Teflon pad 42 on the outside of the outer plate 1 to find the depth position of the main deck 3 on the side of the outer plate 1.

[0044] like Figure 1 As shown, the thickness of the 30cm steel ruler 43 does not exceed 0.5mm. Therefore, it can be inserted into the small gap between the water curtain spray device 2 and the outer panel 1.

[0045] like Figure 1 As shown, the graduations on the 1m steel ruler and the 30cm steel ruler (43) are aligned. Specifically, the surfaces of the 1m steel ruler and the 30cm steel ruler (43) are parallel and aligned, the graduation directions are the same, and the 0 graduation line is aligned.

[0046] like Figure 1 As shown, the Teflon pad 42 is installed 100mm from the bottom of the 30cm steel ruler 43. Given that LNG ships are typically designed with a tongue-and-groove joint height of 100mm on the outer plating, the Teflon pad should be installed 100mm from the bottom of the 30cm ruler to ensure that while it rests on the tongue and groove joint to compact it, the bottom of the 30cm ruler touches the main deck 3.

[0047] like Figure 1 As shown, the thickness of the Teflon pad 42 is 25-30mm. If the Teflon pad 42 is too thin, it will not be able to hold the tongue and groove plate properly; if it is too thick, it will cause poor stability of the clamp and affect the measurement.

[0048] In step 6, if the measured depth of main deck 3 exceeds the standard, measure main deck 3 in advance or carry out fire correction and plate replacement. Early detection and resolution of problems prevent surveying errors from leading to substandard quality after delivery.

[0049] This embodiment is merely a further explanation of the present invention and is not intended to limit the present invention. Those skilled in the art can make non-inventive modifications to this embodiment as needed after reading this specification, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A method for measuring freeboard markings on LNG carriers, characterized in that, The method includes the following steps: Step 1: Select any point on the dock pier at the bottom of the ship as the reference height for total station measurement; Step 2: According to the whole ship bottom baseline measurement table, select the corresponding rib points on the bottom outer plate of the longitudinal section of the ship, place the laser measurement target, use a total station to measure the height difference between each point on the outer side of the outer plate and the reference point on the dock, and fill the height measurement value of each rib point into the whole ship bottom baseline measurement table. Step 3: Add the plate thickness at the corresponding rib location to the measured value in Step 2 to obtain the actual value and fill it in the whole ship bottom baseline measurement table; Step 4: Calculate the average value of the actual values ​​of each rib point. The average value is the reference height of the bottom baseline. Step 5: Using a clamp, transfer the height of the top of the main deck to the outside of the outer plating; Step 6: Place the 1m long steel ruler in the clamp on the outside of the outer plate, measure the height difference between the 30cm mark of the 1m long steel ruler and the reference height of the bottom baseline, obtain the actual mold depth of the freeboard mark installation position, and record the actual mold depth. Step 7: Subtract the theoretical height from the freeboard mark to the bottom baseline from the actual measured depth. This gives the actual survey height from the 30cm mark on a 1m steel ruler to the freeboard mark. Step 8: Based on the actual survey height, mark the outer plate reference mark at the 30cm mark position on the 1m long steel ruler, measure the survey height downwards, and obtain the drawing position of the freeboard mark.

2. The method for measuring the freeboard markings of LNG carriers according to claim 1, characterized in that, In step 2, the selected rib sites cover the entire ship, and the number of rib sites is 20-30.

3. The method for measuring freeboard markings on LNG carriers according to claim 1, characterized in that, The measuring tape includes a 1m long steel ruler, a Teflon pad, a 30cm steel ruler, bolts, and washers. During measurement, the 1m long steel ruler is suspended on the outside of the tongue and groove joint of the outer panel, the Teflon pad is located on the tongue and groove joint of the outer panel, and the 30cm steel ruler is placed on the inside of the tongue and groove joint of the outer panel. The 1m long steel ruler, the Teflon pad, and the 30cm steel ruler are all provided with screw holes that match the bolts. The 1m long steel ruler, the Teflon pad, and the 30cm steel ruler are fixedly connected by bolts passing through the screw holes and washers.

4. The method for measuring freeboard markings on LNG carriers according to claim 3, characterized in that, The thickness of the 30cm steel ruler shall not exceed 0.5mm.

5. The method for measuring freeboard markings on LNG carriers according to claim 3, characterized in that, The graduations on the 1m long steel ruler and the 30cm steel ruler are aligned.

6. The method for measuring freeboard markings on LNG carriers according to claim 3, characterized in that, The Teflon pad is installed 100mm from the bottom of the 30cm steel ruler.

7. The method for measuring freeboard markings on LNG carriers according to claim 3, characterized in that, The thickness of the Teflon pad is 25-30mm.

8. The method for measuring freeboard markings on LNG carriers according to claim 1, characterized in that, In step 6, if the measured main deck depth is found to be excessive, the main deck should be measured in advance or pyrotechnic correction and replacement of the deck should be carried out.

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