The 24-12-24-12 vision of A2SEA
- 24 hours maximum loading time in port
- 12 hours cycle time for installation (including jack up, installation, jack down and repositioning)
- 24 hours maximum time from mechanical installation until the turbine is ready to produce power
- 12 m/s minimum wind limit for all offshore operations
Length (LOA) x Beam x Depth: 132m x 32m x 9m
Max jackable draft: 5.3 m + (spudcan tip 0.8 to 1.5 m below BL)
Speed: Approx 12 knots
Deck load and area: 15 tons / m2 and 3350 m2 deck area
Payload: 5000 tons
Water depth and leg stroke: Leg length below base line 60 m (stroke). Typical water depth 45 m
With feet the size of 100 square meters, the self-propelled jack-up vessel Sea Installer is A2SEA’s bid for the installation vessel of the future. It is designed with the aim of offering the best and least costly installation for offshore wind turbines and foundations.
By Tea Tramontana
He started to dream of a new vessel eight years ago while at sea - taking part in the installation of Horns Rev.
- Back then we used semi-jack-up vessels and the waves and the wind made the vessel move. A movement of just 20 to 30 millimeters makes the load at the end of the crane move 200 to 300 millimeters and this made working conditions very diffcult. So, I started dreaming of moving the vessel completely out of the water, says Einar Ravneberg, Head of Development at A2SEA.
The dream came true and A2SEA is one of the installation companies now building a self-propelled jack-up vessel designed for future installation of wind turbines offshore.
The name of the vessel under construction in China is Sea Installer, a four legged jack-up vessel. Prior to signing the contract with the Chinese shipyard COSCO there was three years of designing and innovation.
When the jack-up legs of Sea Installer are up they rise 67 meters above sea level
From the mess deck to the bridge
During the design period, the fact of actually being on board A2SEA’s other vessels was essential to Einar Ravneberg and his team of engineers. Speaking and presenting draft designs to everyone, from the mess girl to the captain, they came to understand the ways of working and the challenges experienced by the crew on board.
- To give you an example: we understood the captain’s difficulties working on the bridge because he was not able to stand at his position and look aft under positioning of the vessel and later to follow the loading and unloading. The solution was to lower the staircase to the level of a dining table in order to create a free view in all directions from the bridge, says Einar Ravneberg.
Another example is a better and more effcient way of sorting the laundry of the crew – and yet another is the placement of the crane around one of the jack-up legs:
- Positioning the crane on one of the jackup legs is an idea from the oil industry in a much smaller scale, but we invented a solution adapted for the offshore wind turbine industry. Now nearly all our competitors have copied the idea.
The best estimation
To Einar Ravneberg the biggest challenge designing the Sea Installer was to estimate the height and weight of the loads that Sea Installer will carry
- When we ask the turbine manufacturers how their products will look in 2020 they refuse to reveal any details, but still remind us that we should not forget to make a vessel that we can use to install them! It leaves a great deal of uncertainty, says Einar Ravneberg. Years of experience and know-how therefore became very important and when asked to name the three most important design details that will distinguish Sea Installer and make customers prefer A2SEA to its competitors, Einar Ravneberg responds very quickly:
- It navigates very quickly and with high precision. We can work effciently because of the position of the crane on one of the jack-up legs and the fact that the deck is open makes work on board easier and thus quicker.
How does it work?
The crane is installed around one of the four jack-up legs
It costs around 25 percent more to install the crane on one of the jack-up legs compared to the traditional solution of placing it in the middle of the aft end of the vessel. But conflicts between the leg and the crane are avoided and it makes loading much easier, quicker and therefore less costly.
Three thrusters ensure maneuverability
An inline thruster, a tunnel thruster and a retractable thruster ensure that Sea Installer has enough power to quickly maneuver in and out of installation position. In addition to this high maneuverability, the Voith Schneider propeller system, which is a cycloidal drive system, also ensures that Sea Installer avoids gear problems due to air taken in at the surface.
The spud can is the footon a jack-up leg
The spud can is designed to spread the load so that the jack-up leg does not sink too deeply into the seabed. Water is blown through it when extracting the legs from sea bottom. The diameter of the jack-up legs is 4.5 meters and they are 82 meters long. Each leg is driven by eight cylinders in a hydraulic jacking system.