About this calculator
Project cargo is rarely one uniform object. A pump skid, a plant module, a generator on a frame or an excavator with its boom folded consists of several components with different weights and positions. To plan the lift, the sea-fastening or the position on deck you need one combined centre of gravity (CoG) and the total weight.
The principle is moments: the combined CoG on each axis = Σ(weight × coordinate) ÷ Σ weight. Choose a datum (for example the aft-port-bottom corner of the frame), measure X forward, Y sideways and Z up for each component, and the calculator gives the total weight, combined X, Y, Z and a moment table you can check line by line. Components removed for transport can be taken out simply by deleting their line.
The two-point lift section uses the lever rule: with lifting points A and B on one line, the load at A = W × (x_B − x_CoG) ÷ (x_B − x_A), the rest at B. When the CoG lies outside the two lifting points one load turns negative — the cargo will tip as it is lifted. The result helps choose slings and shackles of unequal length or capacity. For critical cargo the CoG must be confirmed from vendor drawings or weighing; this calculator is for education and estimation.
Worked example
Skid with three components (X, Y, Z from the frame corner):
- Frame 12 t at (3.0; 1.2; 0.4), motor 8 t at (1.5; 1.2; 1.5), pump 5 t at (5.0; 1.0; 1.1)
- Total 25 t; X = (36 + 12 + 25) ÷ 25 = 2.92 m; Y = 29 ÷ 25 = 1.16 m; Z = 22.3 ÷ 25 = 0.892 m
- Lifting point A at X 0.5 m and B at X 5.5 m: A = 25 × (5.5 − 2.92) ÷ 5 = 12.9 t, B = 12.1 t
- The CoG lies between the points, so the load lifts level with sling A slightly heavier
How to use it
Choose a datum
Pick one zero point (for example a frame corner) and the same X, Y, Z directions for all components.
Enter components
Add a line for each component with its weight and centre-of-gravity coordinates.
Read the combined CoG
See the total weight, combined X/Y/Z, moment table and the top and side sketches.
Check the lifting points
Enter the X positions of lifting points A and B to see the load at each and whether the CoG lies between them.