Naval Science 304: Navigation and Naval Operations II

Lesson 12: Underway Replenishment (UNREP)

A. Learning Objectives

1. Know the types of ships involved in underway replenishment.
2. Know basic UNREP procedures, from coming alongside to breaking away.
3. Know basic UNREP communication procedures.
4. Know the equipment associated with replenishment at sea (RAS).
5. Know UNREP safety precautions.

B. Underway Replenishment (UNREP)

1. Definition: A broad term applied to all methods of transferring fuel, munitions, supplies, and personnel from one vessel to another while underway. Another term that you may encounter is Replenishment at Sea (RAS), which applies to all methods except fueling at sea.
2. Why? Clearly, replenishing fuel, ammo, and supplies at sea allows us to stay at sea- and stay on the job.

C. Replenishment Ships

1. There are several types. The function of ammunition ships (AE) and oilers (AO) should be obvious. The fast combat support ship (AOE) provides a combination of oiler/ammunition ship capabilities. The combat stores ship (AFS), sometimes referred to as the "Attack Food Ship" is just that- she provides spare parts, food, and other cargo. Many replenishment ships are now operated by the Military Sealift Command (MSC) which means they are manned primarily by civilians. A "T" in front of the hull number indicates the ship is operated by the MSC and is therefore designated USNS (United States Naval Ship) vice USS (United States Ship). These ships have widely varying capabilities and this is one of the most important things to understand during the underway replenishment planning process, since this will determine our station during replenishment, what stations will be used, etc.

D. Basic Sequence of Events

1. Lifeguard station: If multiple ships are engaged in UNREP, a ship (usually the next customer) will be positioned approximately 1000 yards astern of the delivery and receiving ships. Man overboard is a real danger during UNREP, so the function of the lifeguard ship is exactly as the name implies.
2. Waiting Station: After the previous customer is out of the way, we move up to the waiting station and this is where we begin the sequence of flaghoists and commence our approach.
3. UNREP course and speed: Generally dictated by the delivery ship if UNREP is a two ship event, or by the OTC for a group of ships. Usually chosen to provide the smoothest ride possible, unless it is vitally important that the force continue along a specific heading. Called ROMEO corpen and ROMEO speed. Typically a speed between 12 –16 kts is chosen because of significantly reduced rudder effects for speeds less than 8 kts and bigger ship separation required to counter increased Venturi effect for speeds greater than 16 kts.
4. Approach course and speed: Should be the same as ROMEO corpen with slightly higher speed (usually 3 –5 kts greater than ROMEO speed), with minor adjustments as necessary to execute the approach. From the time we commence our approach until we are clear of the other ship after breakaway, DO NOT use rudder orders to maneuver the ship- only minor course changes are used. A key tool for use during the approach is the radian rule, which mathematically is
          separation distance x (60/range) = angle off the bow (degrees)
And some good values to remember are, for a separation distance of 50 yards (150 feet):
                    1000 yards - 3 degrees
                    500 yards - 6 degrees
                    300 yards - 10 degrees
Once our bow is even with the other ship’s stern, drop speed to ROMEO speed and glide into position. (of course, every ship is a little different and it takes a little experience to determine when to drop the speed).
5. Shot Line: The first thing to come across. After this comes the messenger, and the phone and distance line, which is used for sound powered phone communications between the two ships and for gauging distance. The line has a flag every twenty feet, and they are color coded in the sequence green-red-yellow-blue-white-green (I remember it as "Go rub your belly with grease").  This line is kept taut by linehandlers.
6. Tensioning the span-wire: The bridge of both ships must be alerted before this happens. This is a very important piece of information for the helmsman and the conning officer, since the force exerted by the tensioned span wire will tend to pull the two ships together, and the helmsman will have to compensate with the rudder to maintain the ship on ROMEO corpen.
7. Engage the rig:  The choice of rig depends on the item to be transferred, be it food, fuel, ammunition, other cargo, or personnel.
8. Transfer supplies and/or fuel: Throughout this evolution, the conning officer must pay careful attention to the separation between the two ships. The delivery ship will maintain course and speed, and the conning officer on the receiving ship will make minor course corrections (half a degree at a time!) and speed changes to maintain position. An extremely competent helmsman is essential to success.
9. De-Tension the span-wire: Again, the helmsman and conning officer need to know this is happening
10. "All Lines are Clear:" Once we know this, we increase our speed (but don’t change course just yet!) and once our stern is clear of the delivery ship’s bow we put the rudder over (if desired) and head on our way.
11. Breakaway/Emergency Breakaway: These are the same thing, except the emergency breakaway is done FASTER. We DO NOT cut lines or anything of that sort. (no axes are required for this evolution). Typically, we always end UNREP with an emergency breakaway for practice.

E. UNREP Communications

1. Use of Signal Flags: see page 288, figure 9-10 of Seamanship. Memorize this information.

F. UNREP Equipment

1. Inhaul:  used by the delivery ship to retrieve the load
2. Outhaul:  used by the receiving ship to bring the load across from the delivery ship
3. Span wire:  actually supports the load as it goes across. A trolley is typically used to roll the load along the span wire
4. Ram Tensioner:  on most modern rigs, a ram tensioner is used to automatically maintain the tension on the span wire.
5. Shot Line:  the first line across, fired from rifle.
6. Messenger:  attached to the shot line, used to guide across more substantial lines.
7. Manila Highline:  for a personnel transfer, the ram tensioner and steel span-wire are not used because they do not adequately guard against parting from sudden ship rolls. Therefore, since linehanlers cannot tend wires, manila lines are instead used for the span-wire, outhaul, and inhaul (all must be tended by linehandlers, not winches or tensioners). Synthetic highline (MIL-R-24536) may now also be used as a substitute for manila highline.

G. UNREP Safety

1. All personnel involved wear helmets that are color-coded to indicate their job. (Know these)
2. Other safety issues are discussed on pages 3-30, 31, 36, and 37 of Surface Ship Operations. Ensure you are familiar with these.