Currently, the maximum number of permitted slings in a Tip Hook assembly is 7, i.e. six slings + the boom. It is common industry practice to lift with 9 slings; see attached, where eight slings participate + the boom.
Moses is limited, and we are calling for the increment of the allowable number of slings to 9.
Another requirement is to account for the hook offset; see attached, where the slings are wrapped around the hook. The current tip-hook formulation assumes that all slings meet at one common point, which is not always true.
Using four slings provides a much more accurate representation of the actual rigging arrangement. MOSES is a powerful tool for global hydrodynamics, vessel motions, and total lift wire tensions. However, it simplifies connections as idealized point nodes. It cannot accurately simulate the physical contact, flattening, or sliding of a heavy-duty sling over the curved geometry of a trunnion or hookpronk .
Because of this software limitation, the installation engineer must calculate and apply load distribution factors (such as Skew Load Factors) analytically. These factors account for real-world inequalities that MOSES misses like;
Fabrication Tolerances: Slings are never exactly identical in length.
Rigging Geometry: The specific horizontal and vertical angles of the slings as they go to the hook.
Friction and Shifting: How the slings settle on the trunnion during the initial tensioning.
The engineer typically uses marine warranty standards like DNV-ST-N001 or ISO 19901-6 to dictate the minimum distribution and skew factors based on whether the rigging is dual-hook, single-hook, or utilizes spreader bars.