Navy Emergency Breakaway Failure During Underway Replenishment at Sea.

Underway Dangers at Sea During UNREP of US Navy DDG.

Replenishment at sea (RAS) (North Atlantic Treaty Organisation/Commonwealth of Nations) or underway replenishment (UNREP) (U.S. Navy) is a method of transferring fuel, munitions, and stores from one ship to another while under way. First developed in the early 20th century it was used extensively by the United States Navy as a logistics support technique in the Pacific theatre of World War II, permitting U.S. carrier task forces to remain at sea indefinitely.

nderway replenishment (UNREP)

In order to carry out the Navy's mission effectively, fleet units must be capable of remaining at sea for prolonged periods of time, possibly in areas of the world where friendly resupply ports are not available, and remain fully ready to carry out any assigned tasks. Military Sealift Command (MSC) ships are equipped to replenish combatants underway with fuel, ammunition, provisions, and spare parts. As a result of underway replenishment techniques, the US Navy can remain mission ready to carry out US policy any where in the world.

The first significant underway replenishment (UNREP) operation at sea was with the collier USS Marcellus and the Navy warship USS Massachusetts in 1899. Since this first UNREP, many methods for transferring cargo have been tried. On board the USNS Rappahannock the two major methods of transferring dry cargo are via VERTREP with a helicopter, and wire highline utilizing a standard tensioned replenishment alongside method or STREAM rig.
Underway replenishment (UNREP) is a broad term applied to all methods of transferring fuel, munitions, supplies, and personnel from one ship to another while the vessels are underway. Two general methods of UNREP are used connected (CONREP) and vertical (VERTREP). They may be used singly or at the same time. In connected replenishment, two or more ships steam sidebyside and the hoses and lines used to transfer fuel, ammunition, supplies, and personnel connect the ships.

Vertical replenishment is carried out by helicopters with the ships in close proximity, or miles apart depending on the tactical situation and the amount of cargo to be transferred. Connected replenishment involves two processes refueling and resupply. In fueling at sea (FAS), fuel is pumped from the delivering ship like the USNS Rappahannock, or a Navy vessel such as a fast combat support ship (AOE). Other replenishment ships such as the combat stores ship (AFS) and the ammunition ship (AE) can deliver fuel, but their primary mission is the delivery of dry cargo by methods referred to replenishment at sea (RAS).

There are several factors in favor of replenishment with the ships alongside each other instead of astern. First, by replenishing alongside, the oiler or other auxiliary ship, can service two ships at once, with multiple replenishment stations to each ship. Second, by replenishing alongside rather than astern, the whole formation of ships can maintain greater speed (up to 16 knots instead of the 78 knot maximum for astern refueling). Third, by replenishing alongside, both fuel and dry cargo can be transferred, instead of being limited to fuel only. Astern fueling does have a place in the replenishment plan, but it is generally limited to a tanker in convoy refueling the convoy escorts.
Underway replenishment techniques continue to advance with the introduction of new systems and equipment. STREAM stands for Standard Tensioned Replenishment Alongside Method and is utilized in both RAS and FAS evolutions. The STREAM rig is preferred over other connected replenishment methods as it permits greater ships separation.

When utilizing the STREAM rig for FAS operations a tensioned spanwire is suspended between the two ships. A series of hose saddles are attached to the spanwire by trolleys. The actual transfer hoses are then suspended in between the saddles. The receiving end of the hose rig is tipped with a coupling. A variety of fueling couplings may be used to ensure compatibility between the delivery and receiving ships. The most common is a probe fueling coupling. The probe may be used in the transfer of either DFM or JP5 products. The probe itself has a latching mechanism that holds it in the receiver by spring force. The receiver is mounted on the receiving ship by a swivel arm. The swivel arm allows the receiver to move throughout the full working range of the receiving station, ensuring proper alignment prevents the probe from unseating. The probe assembly will unseat from the receiver when a 2,500 lb. line pull is applied. The receiver also has a manual release lever, which is the desired way to release the probe upon completion of the fuel transfer.

Prior to underway replenishment, coaling stations were the only way to refuel ships far from home.

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