Underway replenishment
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Underway replenishment (UNREP) or replenishment at sea (RAS) is a method of transferring fuel, munitions, and stores from one ship to another while under way.
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[edit] History
Following some early development starting at about 1900 for transferring coal, the technique of underway replenishment was perfected by the United States Navy in the late 1930s and used extensively as a logistics support technique in the Pacific theatre of World War II. Since it allowed extended range and striking capability to naval task forces the technique was classified so that enemy nations could not duplicate it. Presently, most underway replenishments for the United States Navy are handled by the Military Sealift Command. It is now used by most, if not all, blue-water navies.
Germany used specialised submarines (so called "milk-cows") to supply hunter u-boats in the Atlantic during World War II. However, these were relatively ponderous, took a long time to transfer stores, and needed to be in radio contact with the replenished boat, all conspiring to make them rather easy targets. Due to this, they were soon retired from their supply role.
[edit] Methods
There are several methods of performing an underway replenishment.
[edit] Alongside connected replenishment
The alongside connected replenishment, also known as CONREP, is a standard method of transferring fluids, such as fuel, ammunition, and break bulk goods. The supplying ship holds a steady course and speed, generally between 12 and 16 knots. The receiving ship then comes alongside the supplier at a distance of approximately 30 yards. A gunline, or shot line, is fired from the supplier, which is used to pull across a messenger line. This line is used to pull across other equipment such as a distance line, phone line, and the transfer rig lines. As the command ship of the replenishment operation, the supply ship provides all lines and equipment needed for the transfer. Additionally, all commands are directed from the supply ship.
Because of the relative position of the ships, it is possible for some ships to set up multiple transfer rigs, allowing for faster transfer or the transfer of multiple types of stores. Additionally, many tankers are set up to service two receivers at one time, with one being replenished on each side.
In the U.S. Navy, aircraft carriers are always replenished from the port side of the supply ship—the starboard side of the carrier. The design of the aircraft carrier, with its overhanging flight deck, does not permit replenishment from the carrier's port side. Most other ships can receive replenishment from either side of the supply vessel.
Alongside connected replenishment is a risky operation, as two or three ships running side-by-side at speed must hold to precisely the same course and speed for a long period of time. A slight steering error on the part of one of the ships could cause a collision. For this reason, experienced and qualified helmsmen are required during the replenishment, and the crew on the bridge must give their undivided attention to the ship's course and speed. The risk is increased when a replenishment ship is servicing two ships at once.
In case of emergency, crews practice emergency breakaway procedures, where the ships will separate in less-than-optimal situations. Although the ships will be saved from collision, it is possible to lose stores, as the ships may not be able to finish the current transfer.
Following successful completion of replenishment, most ships engage in the commonly practiced custom of playing a signature tune over the replenished vessel's PA system as they break away from the supplying vessel.
[edit] Astern fueling
A rarely used type of replenishment is astern fueling. In this method, the receiving ship follows directly behind the supplying ship. The fuel supplying ship throws a marker buoy into the sea and the receiving ship takes station with it. Then the delivering ship trails a hose in the water that the fuel receiving ship retrieves and connects to receive fuel. This method is more limited, as only one transfer rig can be set up. However, it is safer, as a slight course error will not cause a collision.
[edit] Vertical replenishment
A third type of Underway Replenishment is Vertical Replenishment, or VERTREP. In method, a helicopter lifts cargo from the supplying ship and drops it on the receiving ship. The main advantage of this method is that the ships do not need to be close to each other, so there is little risk of collision. However, the maximum load and transfer speeds both are limited by the capacity of the helicopter.
[edit] See also
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