Nuyina's construction propels ahead
In preparation for the RSV Nuyina’s floating in September (see previous story) a number of critical components of the ship’s propulsion system were installed.
First were the ship’s two ‘gondolas’ – each made of 80 tonnes of steel – which hold the ship’s propeller shafts (see photos).
Australian Antarctic Division Icebreaker Project Manager, Mr Nick Browne, said the complex and precise nature of the gondolas required a specialist team of 27 welders to install them.
“Each gondola was pre-heated to 150°C before welding could commence, as welding cold steel can cause it to expand and contract unevenly, affecting alignment and possibly causing the steel to fracture,” Mr Browne said.
“Each welder spent one hour on the job before another took over, and they had to wear wooden-soled shoes to cope with the heat.”
With the gondolas complete, the propeller shafts could be aligned. The 50 metres-long shafts connect the main engines at the centre of the ship to the 40 tonne propellers (and hubs) at the stern. The shafts each sit inside a ‘stern tube’, which allows them to pass through the hull without water leaking into the ship.
“The propeller shafts were aligned by sending a laser beam through the stern tubes,” Mr Browne said.
“Perfect alignment of the shafts is critical to prevent propeller wobble and structural failure of the shafts, and will contribute to the silent operation of the ship during scientific surveys.”
In open water the main noise on the ship is from the propulsion system – the engines, gear boxes and propellers. This interferes with scientific acoustic instruments and can affect the behaviour of fish and other marine organisms that the scientists want to study (see Australian Antarctic Magazine 34: 2-3, 2018).
With the propeller shafts in place, the propeller hubs, on which the blades are bolted, could be attached. The propeller hubs are made of nickel, aluminium and bronze and are 1.94 metres in diameter and weigh almost 21 tonnes. During operation the hubs are filled with oil to actuate the variable pitch of the propeller.
“Each propeller has four blades made out of stainless steel and weighing about 4.5 tonnes each. The total diameter of the complete propeller is 5.65 metres,” Mr Browne said.
The gondolas and propellers are protected by ice knives at the stern of the ship. These help to split and distribute ice under the vessel after it has been broken up by the weight of the bow. Rudders, each weighing 33.5 tonnes are installed beneath the ice knives.
Finally, six tunnel thrusters help the ship spin on a dime and hold a set position (dynamic positioning) with ±20 m accuracy. Three thrusters at the bow and three at the stern each require 1300 kW of electrical power for maximum thrust. The thrusters will hold the ship in place during deployment of scientific equipment in a range of sea states, as well as during small boat deployment and cargo operations.
Australian Antarctic Division