Figure 6. 
Traditional approaches utilize an overhead crane to 
position the casting near the deck while a structural team 
maintains its proper plane and location. A rough scribe is 
made then the deck is burned. This placement, scribing, 
and burning process is repeated a number of times until 
final placement is achieved. The typical deck installation 
consumes a complete eight hour shift for 1 crane and up 
to 6 people. (The process for side shell installation is 
similar except that in this case the casting is now welded 
into the deck and the shell plating is 'stepped' into place). 
Significant gains are achieved by precutting the deck and 
shell to the shape and proper structural alignment of the 
casting so that the crane merely lifts the object into the 
cutout to be secured and then welded. The difficulties 
associated with establishing accurate measurement 
references and the time consumed measuring and then 
calculating the three dimensional coordinates for this 
object have made traditional theodolite use for this job 
too costly. DPMS techniques rely on the ability to obtain 
measured coordinates quickly and easily. Actual data 
points for the perimeter of the of the casting is then 
imported into CAD software for analysis to design. Then it 
is run through an optical nesting software that creates a 
true sized template to orient and mark out the proper 
burn line (Figure 6) 
The improved burn quality results in no patches, the best 
possible structural alignment, and consistent weld gaps. 
This lessens the structural fit up time which in turn 
positively impacts other jobs for the structural team. Also, 
current vendor quality checks can be modified to take 
advantage of photogrammetric readings and CAD casting 
models to determine acceptance or rejection of the 
270 
product at the foundry. Performing this check at the 
foundry would be much more reflective of the customer 
requirements and allow time for mold modifications if 
needed. 
3.3 Structural Misalignment 
During the fitup and welding of units in the erection 
process one of the most costly areas of unplanned labor 
occurs at the turn of the bilge, in the mid body area, 
where there can be a significant amount of structural 
misalignment from time to time. Here the transition from a 
horizontal bottom to a vertical side shell occurs over a 
three to seven meter distance. Since this happens to be 
an area of high stress there is a lot of support structure 
welded to the interior of the hull. Even though this 
welding is performed while the unit is restrained by mock 
diaphrams to maintain its shape; when it is released, the 
internal forces from welding can still cause distortion. 
Sometimes these forces are so strong that they can even 
distort the hull while it is restrained. Many attempts to 
monitor this movement have been tried over the years 
but none have shown the potential that DPMS techniques 
have thus far. Here the ability to quickly measure three 
dimensional XYZ data and then import the results directly 
into AUTOCAD models of the design hull profile are used 
to analyze the deviations as the subassemblies are built. 
Figure 7 depicts such a comparision between the mock 
diaphrams of the side shells and the hull profile for Unit 
2120. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996 
To date 
and pr 
measure 
for analy 
dimensic 
particula 
knowled 
structure 
of unitco 
3.4 Bur 
One of t 
yard ste 
shapes 
plating. | 
noticed : 
producti: 
undetec 
small de 
Regardl