An advantage of this method is the ease with which construction 
may begin. There is no need for dry docks or polders; instead, construc- 
tion can begin at any time in any quiet water of sufficient depth. The 
construction rate is estimated to be about 500 feet of section per 
month per form. Any number of forms may be used, and the area required 
is considerably less than if the sections were constructed horizontally 
on land. 
The process is a continuous manufacturing technique which results 
in a homogeneous concrete structure with no joints. Like all repetitious 
casting techniques, it is efficient and economical, particularly because 
there is very little equipment needed. The latter is particularly 
advantageous from an investment standpoint, since the major items of 
equipment can and should be conventional items presently available on 
the market. The forms are the only unusual elements, but they should be 
relatively inexpensive to build. 
As far as is known, no large sections have been constructed using 
slip form casting. Some preliminary cost estimates have been derived 
for at least two large vessels which have been proposed as likely 
candidates for the technique. One, a 1,400 foot long supertanker, is 
estimated to cost 250-300 kronors per ton of concrete weight.” At the 
current exchange rate of 5.2 kronors per dollar, this is about $50 to 
$60 per ton or about $100 to $120 per cubic yard. A much smaller vessel 
of 1,000 tons displacement was estimated to cost $200 per cubic yard. 
The cost of the equipment, for construction of the supertanker is estimated 
not to exceed $4,000,000." These cost figures are within 10% of the 
cost estimates given for more conventional methods of concrete construction 
practiced in the continental United States. 
Fabrication of Deck and Hull Elements 
Deck. Deck elements for the elevated or the semi-submersible 
platform are seen as precast, prestressed concrete 'box'' elements, post- 
tensioned in final assembly to obtain an integral deck and for connecting 
to the support elements. The box elements could be sized and tiered to 
meet multiple deck requirements. Solid slab construction appears unlikely 
for the smaller platforms, but probably would be employed in the larger 
platforms in combinations with multiple decks. In optimizing the design, 
the box element could emerge as a likely candidate even for the single 
deck; the depth would satisfy structural requirements while the box 
feature would minimize weight and provide buoyancy. 
* 
Hydro Concrete System, Aktiebolaget Hydro Betong, Stockholm, Sweden, 
IIO6SE ip) 4 ot ‘siecEvon PM No: 3). 
sheet 
Ww 
Ibid., page 2 of Section PM No. 4 
KKK 
Ibid., page 4 of Section PM No. 4 
SO 1) 
