Installation aids for EM Buoy installation Stolt Comex Seaway (SCS) ‐ 1999‐2000

In order to give a better perspective of scale of the control buoy a picture taken during fabrication is shown top left with the 6 m Rhino work boat shown next to the bow catcher boat landing below it. The right hand picture shows the 100 cubic metre stabilising buoy that Wale Marine engineered and fabricated for SCS for the controlled lowering of the 3,000 Te caisson gravity base used for tethering the EM control buoy to the sea‐bed. The right hand picture shows the recovery of the buoy onto the DSV Discovery after successful deployment of the caisson.

The stabilizing buoy was multi‐compartmented to allow for controlled flooding and evacuation of the 11 compartments, with each compartment and its separating bulkhead being capable of resisting 110 m of submergence pressure (110 tonnes per square metre). Wale Marine also supplied and installed all of the piping for the flooding umbilical. Fabrication of the structure was sub‐contracted to Concrete Units in Meyerton with pontoon shells being fabricated from spirally wound pipe. The time between award and delivery was ten weeks. The structure was fabricated in 4 modules in Meyerton (3 x double pontoon units and 1 x central unit) and truck transported down to Cape Town for final assembly, in situ welding and installation of the flooding umbilical. Further pictures of the associated rigging and ancillaries relating to the stabilising buoy and the gravity base and control buoy installation are included below.

The above pictures show the floating caisson being towed from Simonstown to the EM field. These show the temporary tripod structure we designed and supplied together with the deployment pendant for the lowering of the caisson. The Wale Marine supply included the removable steel works platform atop the caisson gravity base. The tripod connections were designed to be compatible with the tether clevises used for anchoring the control buoy, and ten years later we used the same anchorage points for installing the temporary hydraulically operated retractable tether used in the repair works discussed on page 4.

Other equipment supplied by Wale Marine for the project included 100 tonne swivel (top left), the subsea hydraulic shackles for quick release (bottom left), a friction drum tensioning system that we used for spooling of the steel wire rope onto the 50 tonne deployment winch, 50Te SWL deflector sheaves for over‐boarding winch cable from the DSV Discovery, the over‐boarding chutes for umbilicals, chain forks and flooding manifolds, as well as the riser installation winch and 25 tonne SWL deflector sheaves used to install the EM risers onto the FA platform.

The picture above right shows the 120 Tonne SWL emergency replacement snatch block that was used for the installation of the EM Control Buoy onto the gravity base. This snatch block was an emergency replacement block to be used in the pull‐down rigging because the initial block had failed. The order for the works was given to Wale Marine at noon on a Friday and the completed item was designed, built and dispatched by 08h00 the next day, having been tested to 150 tonnes on a test bench. The reported comment from the DSV superintendent on receiving it was “This is almost as quick as ordering pizza”.