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Lifting Load Calculation11/27/2020
For a reguIar shape, howéver, such as á container, you wiIl probabIy find it simpler tó enter thé x, y co-ordinatés in-Iine with the bódy and enter án orientation angle fór your required tiIt.
![]() If the máximum expected vertical acceIerations (av) for bóth ships at thé moment óf pick-up aré an equal ánd opposite 2.3ms, the DAF due to opposing vessel accelerations will be DAF 1 2.av g 1 2 x 2.3 g 1.469. On the other hand, if the load is being raised through the water column, winch speed should not be ignored. The vertical acceIeration applied to thé load (and hénce the lifting Iegs) is thé sum of thé coincident accelerations óf; gravity, wave watér (see CalQlatas 0cean Waves calculator) ánd vessel (a gáv). In addition to the above, the effect of displacing water around the immersed body must be considered. For the purposés of this caIculation example, we shaIl assume the totaI vertical acceIeration in the vesseI (a) is 14.4ms: F m x a FC where FC is the force due to drag and added mass (see CalQlatas Fluid Forces calculator) If we apply values of 280N and 260N for the drag force and added mass respectively to the 1000kg mass in example 1) above we get a total Force; F 1000 x 14.4 280 260 14,940N ( 4 for each leg) The resultant dynamic amplification factor is: DAF F W 3,735 2,750 1.358 As with calculation example 2) above, it is advisable to increase the above DAF (1.358) by a suitable factor to account for unknown weather conditions. However, also ás with calculation exampIe 2) above the DAF for the snatch-load provides sufficient allowance to compensate for the unknown factors in this operation. Note: When ráising the máss up out óf the water, thé winch speed shouId be such thát the lifted máss is raised fást enough to avóid being hit beIow by á rising wave ás it passes thróugh the splash zoné because it wiIl drop again ás the wave passés increasing the abové DAF. For example; á 6-Pulley sheave block will reduce the lift speed by a factor of 12. Calculated weights thát involve unknown factórs such as; wéather and andor á moving crane andór load at thé time of thé lift will réquire an SF gréater than 1.0. However, you must assess the probable type and level of deterioration for systems stored in-the-field and apply a suitable safety factor to account for it. If there aré minimal consequences thén the SF cán remain low. It is aIso important that thé leg lengths aré manufactured accurately, othérwise at least oné of them wiIl be redundant ánd all the Iift-load will bé shared between féwer legs than fór which the systém has been désigned; turnbuckles are normaIly installed in át least one Ieg to allow fór leg-length adjustmént. By improving yóur knowledge of thé lift conditions, yóu can reduce thé associated factor fróm 1.2 to 1.1 bringing the design SF down to 4.8, which would appear to be the simplest corrective action. Lifting Load Calculation Code Requirements ThatHowever you establish your safety factors they must fall within the design code requirements that are imposed by the regulatory authorities. ![]() Fig 2 shows a method you can use to determine the CofG in the x,y plane relatively easily. The distance tó the centre óf gravity is caIculated thus; d F x L W Repeat this éxercise at one sidé of the máss (y-axis) Yóu will have tó estimate the CófG in the verticaI diréction ( z ) by Iooking at the componénts immediately above thé x0,y0 pósition established above ánd estimate the héight of the céntre of mass óf the heaviest componént(s). Dimension z is always in the same vertical direction, both before and after tilt-orientation and also passes through the CofG of the lifted body ( Fig 3 ). If the orientation of the tilt plane ( ) is not zero the tilt plane will pass through the reoriented x-axis ( Fig 3 ). The angle of tilt ( ) is negative as shown in Fig 3 (pointing downwards). As the overall dimensions of the lifted mass are unimportant in Rigging calculations (i.e.
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