Fabrication and Installation - Offshore Structures: Design, Construction and Maintenance - page 338

Weight control should be performed by means of a well-defined, documented
system, in accordance with current good practice, such as ISO Draft International
Standard ISO/DIS 19901

- 5 —“ Petroleum and natural gas industries — specific

requirements for offshore structures — Part 5: Weight control during engineering

and construction. ”

Where a limiting design sea state is derived by calculation or model tests,
the limiting operational sea state should not exceed (0.7

× the limiting design

sea state).

Calculated Weight

Class A weight control will be needed if the project is weight- or center-of-
gravity

●

sensitive for lifting and marine operations, or has many contractors
to interface

-

Class B weight control applies to projects where the focus on weight and
center of gravity is less critical for lifting and marine operations

●

Class C weight control applies to projects where the requirements for weight
and center-of-gravity data are not critical

●

Unless it can be shown that a particular structure and specific lift operation are
not weight- or center-of-gravity sensitive, then Class A weight control will be

needed. If the weight estimate is for likelihood accuracy 50%, then a reserve of
not less than 5% should be applied. The extremes of the center-of-gravity envel-
ope should be used.
A reserve of not less than 3% should be applied to the final weighed weight.

-

Gross weight = calculated or weighed weight × reserve (5.1)

Unless operation-specific calculations show otherwise, for lifts by a single
vessel, the dynamic amplification factors (DAF) should be applied as in
Table 5.5 . Alternatively, the DAF may be derived from a suitable calculation
or model test.

TABLE 5.5 DAF in Different Locations

Onshore
Moving Gross Weight, W (tons) Offshore Inshore Static

W ≤ 100 1.30 1.15 1.15 1.0

100 < W ≤ 1000 1.20 1.10 1.10 1.0

1000 < W ≤ 2500 1.15 1.05 1.05 1.0

W > 2500 1.10 1.05 1.05 1.0