Unit Erection

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Experience of previous ship erection schedules and difficulties given the
yard’s physical and equipment constraints leads to standard practices being
established. These are taken into consideration at the structural design stage
as are the desirability of minimising positional welding and fairing. In
general it is common practice to make a start in the region of the machinery
spaces aft, working from the bottom upwards, and also forward and aft, this
area requires larger amount of finishing work. In particular the boring of the
stern for the tail shaft is preferably undertaken when the after sections are
fully faired and welded.

Typical erection sequences for a bulk carrier are shown in Figure below.


In erecting the ship units it is important to employ the correct welding
sequences. These are arranged to avoid excessive ‘locked in’ stresses; and
overlapping frames, longitudinals, stiffeners etc. may be left unwelded across
unit seams and butts until these are completed.

In erecting units, tolerances are a problem, more so on 3-dimensional units
than with 2-dimensional units and particularly at the shaped ends of the ship.
Quality control procedures in the manufacturing shops to ensure correct
dimensioning and alignment are very necessary if time-consuming, expensive and
arduous work at the berth is to be avoided. Improvements in this area have been
made with the use of accurate jigs for curved shell units, planned weld
sequences, and use of lower heat input welding equipment dimensional checks on
piece parts, and the use of laser alignment tools for setting up datums and
checking interfaces.

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