Trans RINA, Vol 153, Part A1, Intl J Maritime Eng, Jan-Mar 2011
The semi-submersible costs more to build and to operate. Ballast controls are similar to those for a submarine
o mono-hull barges are a cheaper option.
It could be concluded that for an accommodation vessel in medium and benign waters (up to 6 metre wave seas) a mono-hull barge is a better option than a semi- submersible barge. But in harsh environments, like the northern North Sea, semi-submersible barges are the preferred option.
6.2 CLASSIFICATION Semi-submersible barges are normally not
called
“barges” as this term is widely used for mono-hull barges. Both in IMO and in Classification Societies, rules for mono-hull barges are included in rules for ships, while the semi-submersibles have separate rules. The IMO MODU Code is an accredited design and operational guideline for Mobile Offshore Drilling Units of the semi-submersible type. Classification Societies also have different
standards
structures and ships. Accommodation semi-submersible barges are normally included in the class notation Column Stabilized Accommodation Unit, similarly in DNV (Recommended Practice DNV-RP-C103) and ABS, that also should comply with IMO MODU Code. Recommended Practice DNV-RP-C103 states:
“The methods outlined in this RP are mainly developed for the analyses of twin pontoon units and ring pontoon units. Consequently this should be taken into account when other concepts are considered. Ring pontoon designs normally
have one continuous
Therefore, two types of accommodation semi- submersibles
barges can be distinguished: DP and
moored units. Examples of both types are given in the next paragraphs.
6.2 (a) Safe Scandinavia
Safe Scandinavia, owned by Prosafe AS and built in 1984, is an accommodation platform with a 12 point chain mooring system, allowing station keeping in the harshest of environments. It is also equipped with a transfer gangway and cranes.
Figure 14: Safe Scandinavia flotel for offshore
Technical features Length: Beam:
Draught: Capacity:
106 m 98 m
Transit: 7m; Operation: Survival: 18m; (incl. Thrusters) 583 Persons workstations
Total Cost: lower hull
(pontoons and nodes) supporting 4-8 vertical columns. The vertical columns are supporting the upper hull (deck).
Twin pontoon designs normally have two lower hulls (pontoons), each supporting 2-4 vertical columns. The 4-8 vertical columns are supporting the upper hull (deck). In addition the unit may be strengthened with diagonal braces supporting the deck and horizontal braces connecting the pontoons or columns.”
There are basically two ways of keeping the unit in
position: — mooring by anchor lines (passive mooring system) — dynamic positioning by thrusters (active mooring system).
A combination of these methods may also be utilized. The units are normally designed to serve at least one of the following functions: — production — drilling — accommodation — special services (e.g. diving support vessel, general service, pipe laying vessel, etc.).”
6.2 (b) Floatel Superior
Floatel Superior owned by Floatel International Ltd. is a flotel
delivered in early 2010 and designed for
operations in the North Sea including the Norwegian Continental Shelf, an area with some of the harshest environmental conditions in the world. It is equipped with offshore gangways
for personnel transfer and
positioning systems for unlimited water depth consisting on a DP3 positioning system and an 8 point mooring system.
22m; and 59
Class: DNV 1A1 Column Stabilized Unit, EO, Non-self-propelled, HELDK, SBM -
Figure 15: Floatel Superior
A-50
©2011: The Royal Institution of Naval Architects
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