Shackle: the rating is the maker's
The tool does not rate a shackle. The working load limit comes from the maker's data sheet (ASME B30.26 puts the rating and the design factor with the manufacturer). What the tool checks is that the shackle can be used on this lug, in four lines. The pin passes the hole: D_pin ≤ D_hole. The plate with its cheek plates fits the jaw: t + 2·t_p ≤ jaw width. The bow clears the lug top: R − D_pin/2 ≤ inside length, with a note to add the sling or hook. And the lug load, on W_E, does not exceed the working load limit.
The load compared is W_E, not W_L, because the maker's design factor of 5:1 or 6:1 already carries impact. For a tailing lug it is the lug resultant; for a lifting lug it is √(sling² + lateral²), the sling load including its spread. The pin-to-hole ratio is also what drives C_r in BTH-1 (3-48): a loose pin, D_p/D_h at or below 0.9, loses pinhole strength.
55 t shackle on the 40 mm lug, tail load 249.5 kN
| Working load limit | 55·9.80665 = 539.4 kN; load 249.5 kN: ratio 0.46 |
| Pin through the hole | 70 against 76 mm: ratio 0.92 |
| Jaw | plate 40 mm against jaw 105 mm: ratio 0.38 |
| Bow | 150 − 35 = 115 mm against inside length 330 mm: ratio 0.35 |
Shackle dimensions in the example are the defaults in the panel for a bolt-type anchor shackle; the real values come from the data sheet.
Pipe trunnion (Moss 10-8 Type 3)
A trunnion is a pipe welded to the shell without a hole, with the sling at a distance e from the shell. The load square to the trunnion is the lift load across and along the vessel axis, V = √(transverse² + axial²); the sling spread pulls along the trunnion, F_a. All on the factored lift load W_L.
273.1 × 15.09 pipe, e = 200 mm, top lug at 30°, K_L = 1.8
| Section | D_i = 242.92 mm; A = 12231 mm²; Z = 7.48·10⁵ mm³ |
| Load | f = 75.9 kN per lug on W_E, 136.6 kN on W_L; V = 136.6 kN, F_a = 13.7 kN (10 % side load, no sling spread) |
| Bending | M = 136600·200 = 27.3·10⁶ N·mm; σ_b = 36.5 MPa against 0.66·260 = 171.6: ratio 0.21 |
| Shear, pull | 2V/A = 22.3 MPa against 104; σ_a = 1.1 MPa; interaction 0.22 |
| Root weld | M/(π·R_n²) = 466 N/mm, plus 16 from the pull, shear 318 N/mm: f = 578 N/mm, f/F_s = 5.3 mm; the 9.5 mm floor governs, throat 12 mm gives ratio 0.79 |
F_y = 260 MPa is an example value; the tool uses the lug material table.
Limits
- The trunnion check is a beam-and-weld hand check. The local stress in the shell under the trunnion is not in it; the FE model supplies that, and as early-access output.
- There is no sleeve, pin or retaining-plate check for the sling end of the trunnion.
- The shackle check does not verify side loading limits of the shackle; the maker's data sheet governs.