1506 
ing are of similar size to those mentioned in 
the previous section on fixed-base offshore 
platforms and the accuracy of measurement 
required is comparable. Consequently the 
units may be photographed, controlled, and 
measured in exactly the same way as those of 
the fixed-base offshore platforms. To date, 
many units and sub-assemblies have been 
measured photogrammetrically. Typical of 
them is the bulbous bow unit (Figure 3) 
where discrepancies of up to 30 mm were 
found between the design and as-built di- 
mensions. 
The problem of ensuring equivalence of 
adjacent units becomes even more acute 
when attempting to join complete half-ship 
units when afloat and in tidal waters subject 
to inclement weather. The need for any fair- 
ing during the joining operation must now be 
eliminated as far as possible so that the weld- 
ing together of the two halves may be ex- 
peditiously carried out. To achieve this, a 
comprehensive record of every part of the 
mating face prior to launching must be made. 
Since the first half-ship will have been 
launched prior to erection of the second, no 
adjustments are possible on it. Following 
measurement of the second half, however, 
modifications may be made to ensure a per- 
fect match with the first half before it is 
launched. This is again a situation ideally 
suited for photogrammetric measurement 
and a trial has been conducted to assess the 
dimensional equivalence of the mating faces 
of a supertanker. 
The application of photogrammetry in the 
hull assembly process is just one of many 
existing, or potential, applications in the 
shipbuilding industry (Weinert, 1969). The 
additional applications fall into three main 
categories: 
(1) Applications involving the measurement of 
models in order to obtain constructional 
(full size) dimensions. An example is the 
     
        
p 3 cowie By E C 
Fic. 3. The bulbous bow unit of a ship being 
photographed with Galileo-Santoni Type A 
stereocamera on a 2m base bar. 
WR ap 
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING, 1975 
work reported by Smith (1971) on models of 
engine room arrangements. 
(2) Applications concerned with the meas- 
urement of transitory conditions, usually 
in association with model experiments. For 
example, the wave patterns around a ship 
during towing trials may be conveniently 
measured photogrammetrically. 
(3) Applications to determine the accuracy of 
blanks, moulds, and end products in the 
manufacture of ships’ propellers (Knodler 
and Kupke, 1974). 
EXAMPLE—A SUPERTANKER BuirT IN Two 
HALVES 
The first vessel in the history of British 
shipbuilding to have been built by the half- 
ship construction technique was launched in 
1973. This ship, a 258,000 ton deadweight 
tanker, is 345 m long. The stern section 
(length 214m) was built first and launched. It 
was joined to the bow section (length 131m), 
built on the same berth immediately after- 
wards, some 10 months later. 
In order to ensure the success of the joining 
operation, it was essential to assess the di- 
mensional equivalence of the mating mid- 
ship faces which measured 50m in width by 
30m in height (Figure 4). To mark off the 
leading edge of each section to form a datum 
plane, which was perpendicular to the ship’s 
centreline and lay in the plane of declivity of 
the ship, a proven laser beam technique was 
used by the shipbuilders. Following this, an 
accurate record of the hardspots lying in this 
datum plane was needed. The hardspots 
were taken as the intersections of each lon- 
gitudinal or longitudinal bulkhead with the 
shell plate and totalled 234 points for each 
midship face. The coordinate system adopted 
is shown in Figure 5. 
With little experience in the half-ship con- 
struction technique, the shipbuilders were 
anxious to obtain as many measurements as 
possible on each half by a variety of methods. 
    
Fic. 4. The midship section of the stern por- 
tion of the supertanker. 
=