Feature article How It Works: Replenishment at sea

Naval ships must remain at sea for long periods of time without food and fuel. As a result, many vessels must replenish at sea. This involves a supply ship, equipped with a Rolls-Royce electric Replenishment at Sea (RAS) system, sailing in close proximity (sometimes just 24 metres apart – the length of six cars) and transferring the necessary supplies across. 1 Gun Line Refuelling a ship is not as simple as visiting a petrol station to refuel your car. It begins with a ‘gun-line’ being fired over from one ship to the other in close proximity. Once the line has reached the ship it will be tied to a heavier line (known as a hose line) to be pulled across, first by hand and then by a winch. 2 Jackstay A steel cable called a jackstay will come over connected to the hose line. This is then attached to the receiving ship and brought up under tension by an autotensioning winch on the supply ship. The jackstay wire will normally sit at about a 45-degree angle from the supply ship, so the fuel hose can be lowered down the jackstay. 3 Fuel Hose The hose will transfer the fuel between ships once connected. It’s not just fuel that can be supplied at sea, however. Stores, food, and ammunition can be transferred in a similar way, with a traveller block moving back and forth between ships on inhaul and outhaul cables. 4 Operator's Console RAS is a complex procedure that requires a high level of accuracy. A single operator on the supply ship uses joysticks, control systems and diagnostics to oversee the replenishment. Did you know? ? Rolls-Royce RAS systems are designed to operate at ship distances from 24 to 61 metres and at ship speeds between 10 and 16 knots. ? Rolls-Royce has supplied Britain’s Royal Fleet Auxiliary and other international navies with RAS stores and systems for over 50 years. ? Rolls-Royce use electric winches to carry out the RAS. The advantages of electric drive include good controllability and reduced through life costs compared to hydraulic systems. ? A new heavy replenishment-at-sea system (HRAS) is being developed that will permit loads of up to five tonnes to be safely transferred between ships. Click for photo release at www.thaipr.net

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