All ships have lifting eye provided for lifting motors, their parts, and other equipments. The following procedure describes how to verify the strength of the lifting eye

Design load (P) = Safe Working Load (SWL) x Dynamic coefficient (Dynamic coefficient is taken as 1.3. recommended by Classification society rules)

Allowable stress

Tensile stress, σa = Yield limit / (1.5 k) = 235 ƒ1 / (1.5 k)

Shear stress, τa = σa / √3 = 235 ƒ1 / (1.5 k x √3 )

where k = 0.85 (mild steel) and 1.0 for high tensile steel, and ƒ1 = 1.0 (mild steel), 1.08 (AH27), 1.28 (AH32), 1.35 (AH34), 1.39 (AH36), 1.43 (AH40)


Required section area for shear stress, Ars

For shear stress the area shown by the hatch on the righ section is applicable.

Ars = P / τa = 1.3 x SWL / (235 ƒ1 / (1.5 k x √3 )) = (3.38 x k x SWL) / 235 ƒ1

Actual section area for shear stress, Aas

Aas = b x t (as shown in the shaded area on the right section)

Required section for tensile stress, Art

For tensile stress, the area is shown by two shaded hatch on the lower part is applicable.

Art = P / σa = 1.3 x SWL / ( 235 ƒ1 / (1.5 k)) = (1.95 x k x SWL) / 235 ƒ1

Actual section area for tensile stress, Aat

Aat = 2 x b x t (as shown by two shaded hatch on the lower drawing)

Evaluation

Aas ≥ Ars (satisfies shear stress requirement )and
Aat ≥ Art (satisfies tensile stress requirement)