Donut Safeland is the leading manufacturer of personal control descent devices for high-rise buildings. Its...
The TEMPSC orientation and evacuation system (TOES) is a retrofit lifeboat (survival craft) enhancement originally designed with support from Chevron in the early 1990s. Since its first installation on Chevron’s Ninian north platform it has since been installed on the Tartan A (initially Texaco and now Talisman Energy).
TOES is simplicity itself, utilising the force of gravity on a tethered wire between the bow of the lifeboat via an anchor on the seabed and attached to a buoy. Once the lifeboat reaches the water and is released from the falls, gravity takes over resulting in the taut wire sinking and the lifeboat moves off in the direction of the wire.
The original concept arose in one of those typical late night discussions following the success and installation of the Donut personal escape device and liferaft enhancement system across various offshore installations. “What can we do next? What else can we do to improve offshore escape and evacuation performance?” The answer came from Donut Safety System’s technical team and Chevron UK, a key sponsor in relation to Chevron’s single fall survival craft in the North Sea.
The capsules had an exemplary performance afloat and a proven release from the single fall. However, despite the fall being made from anti-twist wire it was impossible to predict the orientation of the craft at the point it entered the water. TOES was conceived.
Extensive model trials had utilised the motive force of the buoy to tow the boat. The full scale trials proved the theories of the gravitational pull on the wire, producing near maximum hull speed in the correct direction at the point when it was most vulnerable, release for the falls.
Improved orientation and escape capability
Now we had a simple, passive, inherently safe design with a guaranteed towing force in a known direction. This was at a point when normally the boat would be at its most vulnerable, stationary and hence with little or no manoeuvrability in close proximity to the installation. Earlier studies had shown that at this time the TEMPSC was subject to setback to the point that it could be driven aft under the jacket. TOES now offered a major benefit not only to orientation but to the overall escape capability.
The benefit was not lost with another operator, Texaco North Sea UK Company, who unlike Chevron UK was using Schat Harding twin fall lifecraft. At this time Texaco North Sea was enhancing the Tartan A with a new temporary refuge. As part of this work all TEMPSC were to be located on the same windward side. Studies showed that there was a clear benefit to their escape performance in these conditions.
Gravity and hence water depth is key to the TOES principle. TOES has a proven track record in the North Sea deepwater (120m) and by changing the configuration of the anchor block it has been demonstrated to work in shallow (30m) water with the same benefits of orientation but with less of a towing force for a shorter time.
Customised solution for Rowan Drilling
So to the present. Rowan Drilling has an established reputation for deepwater jack-up drilling with its Super Gorilla class vessels. One of the difficulties penetrating the Norwegian market was their single fall survival craft. Whilst these were proven suitable for marine deployment, like the Chevron boats they did not have a predefined heading at the point at which they entered the water. This is a key point of Norwegian legislation which requires the lifeboats to depart perpendicular to the installation.
The Rowan engineering team approached Donut Safety Systems and, in months of careful engineering, developed with Donut and their engineering consultants Acona a solution to enable TOES to be fitted to all six of their survival crafts on the Rowan Gorilla VI jack-up. In this particular case the orientation of the survival craft was key: any motive force for the installation was a bonus.
The location of the wire retaining rods was key to the design with little room for engineering. The length of the topsides wire was greater than it had been designed previously, but the ingenuity and persistence of the engineering team provided a simple elegant solution of routing the wires under the hull whilst retaining sufficient separation.
As much as possible of the installation was carried out in dock during the rig refurbishment, leaving only the final wire and anchor deployment to be carried out once jacked down on location.
Simple and safe design
Weather will always play a key part in any operation and whilst as much overside work had been designed out, praise has to go to the RGVI crew for their patience and perseverance during the installation. The orientation of the survival craft was emphatic, to the point that the guides were modified to retard the rate of turning, but the test boat was launched to Rowan’s satisfaction and the system approved by the US coastguard. Subsequently the Rowan Gorilla VI received AoC to operate on the Norwegian continental shelf. Rowan has wholeheartedly embraced the simplicity of TOES and its inherently safe design and anticipate installing it again when required in the future.