MEASUREMENT OF MARINE STRUCTURES 
datum plane 
  
+ datum point 
    
baseline 
Fıc.5 The coordinate system adopted for meas- 
urement on the midship section. 
As a result, photogrammetry was added to the 
methods used on this ship. 
The photography was taken using a 
Galileo-Santoni Type A stereometric camera 
(f = 150mm, format 130mm X 180mm) de- 
tached from the supporting base bar and held 
in a special mounting head with the greater 
format dimension vertical (Figure 6). A cam- 
era to subject distance of 16m was selected in 
an attempt to achieve the desired accuracy of 
+ 3mm for the X and Y coordinates. From this 
distance two strips, each containing thirteen 
photographs, were needed to cover the mid- 
ship face after allowing for the usual overlaps. 
The only practical way to gain the neces- 
sary height for the camera stations of each 
strip (7m and 20.5m above the base of the 
ship) was to position the camera on a platform 
suspended from the Goliath crane which 
straddles the building berth. This created 
photographic problems owing to the con- 
tinual movement of the camera platform. A 
viewfinder was fitted to the camera and guide 
lines positioned on the section, to indicate 
the coverage required for each photograph, in 
an effort to overcome these problems. 
Because of the continual demand for this 
crane during the working week and for other 
operational reasons, each midship face was 
photographed during a rest weekend when 
virtually complete and awaiting launch. 
Photography of the stern section was taken 
two weeks before launching but the bow sec- 
tion was photographed 11 weeks prior to 
launch so as to allow time for any modifica- 
tions. On both occasions the weather on the 
days made available for photography was far 
from ideal. 
A number of points on the face were 
targeted prior to photography to serve as 
photo control. The points were later coordi- 
1507 
  
Fic. 6. The Galileo-Santoni metric 
camera in position on the camera plat- 
form whilst photographing the bow 
portion of the supertanker. This plat- 
form is suspended from the Goliath 
crane. 
nated from angular measurements taken with 
a Wild T2 theodolite from survey stations at 
the ends of a baseline running at right angles 
to the ship’s centreline. The baseline was 
measured with a Tellurometer MA100. The 
control point positions were selected so as to 
give a good distribution throughout each strip 
and to allow adequate joining of the strips. 
Analysis of the photography was carried 
out on a Wild A7 plotting instrument equip- 
ped with EK5a coordinate recorder. For each 
strip, a strip triangulation was performed by 
the method of independent models (AIM). 
Natural detail points occurring on the struc- 
ture were used as pass points. Since the final 
form of the measurements was a set of coordi- 
nates of the hardspots lying in the plane of the 
midship section, it was possible to measure 
these points on each model at the same time 
as the triangulation was progressing. Each 
model had, therefore, only to be set up once 
and the as-built coordinates of the hardspots 
were output along with the control and pass 
points following strip adjustment. A block ad- 
justment was not applied and mean coordi- 
nate values were accepted for all hardspots 
in the lateral overlap of the strips. 
The results indicate a RMS error of + 6mm 
in the X and Y coordinates as derived by 
photogrammetry. Plate l is a plot showing the 
shape of the as-built midship sections