MEASUREMENT OF MARINE STRUCTURES 
1505 
TABLE 2. COMPUTED RADII AND RMS ERRORS OF THE BEST FIT CIRCLES TO THE 
MEASURED POINTS TOGETHER WITH THE DISTANCES BETWEEN DERIVED AND 
MARKED CENTRES FOR EACH TUBE. 
  
  
Tube Computed Radius RMS error Distance Between Derived 
(mm) (mm) and Marked Centre (mm) 
1 430.9 +1.0 2.5 
2 430.6 +1.0 2.9 
3 430.2 +1.3 5.1 
4 430.8 +0.7 0.4 
5 430.7 =0.7 1.4 
6 430.1 +15 2.0 
7 430.8 xz11 1.3 
8 430.5 +1.0 1.4 
9 431.1 +1.9 2.4 
10 430.9 =0.7 0.9 
11 431.6 +=1.0 1.7 
12 431.7 +2.0 0.9 
13 431.6 +=1.1 2.3 
14 431.2 +14 1.8 
15 432.1 +1.0 0 
RMS error +2.2 
  
Tyne and the British Ship Research Associa- 
tion (BSRA) have collaborated to examine the 
feasibility of adopting photogrammetric 
techniques as an integral part of the ship- 
building production process. 
At the present time, two important de- 
velopments are taking place in the ship 
production process. First, with the consolida- 
tion of shipyards into large groups, ithas been 
possible to concentrate production of units in 
fabrication shops which may be some dis- 
tance away from the yard where the ship is 
being erected. A further stage in this de- 
velopment is the construction of part-ships in 
one or more yards for final joining afloat or in 
dry-dock. This building technique has al- 
ready been used by the AKER group in Nor- 
way where part-ships were built by the Bergen 
Mekeniske Verksteder shipyard, launched, 
and then towed to the Stord Verft shipyard, 
some 50 km. away, for joining to the remain- 
ing part-ship under construction at Stord. 
The second development is due to the in- 
crease in the size of ships, in particular tank- 
ers, beyond the capacity of many existing 
berths and building docks. The ship must 
then be built as two sections in series on the 
berth and then welded together when afloat. 
This method has been successfully employed 
by the Nederlandsche Dok en Scheepsbouw 
Mij. in Holland and, more recently, by the 
Scott-Lithgow Group in Britain, who have 
adopted it as practice. 
Both of these developments have created a 
demand for rigorous checks on quality con- 
trol at all stages of production in order to 
maintain an efficient hull assembly process. 
To meet this demand, new techniques are 
being considered for acquiring quality con- 
trol measurements. One of these techniques 
is photogrammetry. 
Discrepancies, though usually small, fre- 
quently occur between the design and as- 
built dimensions of units and sub- 
assemblies. Where adjoining units are being 
fabricated in the same shop and close to the 
berth, the checking of the as-built dimen- 
sions of each structure and its relationship to 
the adjoining structure is fairly simple and 
has created few problems. Procedures for the 
feedback of information from berth to fabrica- 
tion shop can be established so that the di- 
mensions of subsequent units may be ad- 
justed at the time of manufacture. 
When fabrication is in shops remote from 
the berth, any checking and, if necessary, 
modification must be done before the struc- 
ture is moved to the berth. In this way 
minimum time and effort are expended on 
the rectification of errors during the erection 
process. 
The use of numerically-controlled 
machines for cutting steel plate has improved 
the dimensional accuracy of units and sub- 
assemblies. Nevertheless it is still necessary 
to check them to see that they meet given 
accuracy requirements. Further, any check- 
ing must be done as swiftly as possible so that 
no delays occur in the erection process due to 
the non-availability of particular units. 
Photogrammetry, with its ability to measure 
accurately in three dimensions and to record 
rapidly a condition with little disruption to 
production work, would seem ideally suited 
to this task. 
The units and sub-assemblies in shipbuild-