HOLES IN THE HULL

Any rupture, break, or hole in the ship's outer hull plating, particularly below the waterline, can allow seawater to enter the ship. If flooding continues uncontrolled, the ship will sink. When the underwater hull is pierced, there are only two possible courses of action. The first, obviously, is to plug the holes or openings. The second is to establish and maintain flooding boundaries within the ship to prevent further progress of the flooding. Dewatering can be effective only after these two measures have been taken.

There is one very important thing to remember about flooding: a ship can sink just as easily from a series of small and insignificant looking holes as it can from one large and more dramatic looking hole. The natural tendency is to attack the obvious damage first and to overlook the smaller holes in the hull and in interior bulkheads. You may waste hours trying to patch large holes in already flooded compartments. Meanwhile, you disregard the smaller holes through which progressive flooding is taking place. In many cases, it would be better to concentrate on the smaller holes. As a rule, the really large holes in the underwater hull cannot be repaired until the ship is dry-docked.

All holes in the hull, large or small, should be plugged completely as soon as possible. As an interim measure, all holes should be partially

plugged if they cannot be completely plugged. Even a partial plug can substantially reduce the amount of water entering the ship. This will substantially reduce the danger of sinking.

Holes in the hull that are at or just above the waterline should be given immediate attention. Holes in this location may not appear to be dangerous but they are. As the ship rolls or loses buoyancy, the holes become submerged and allow water to enter at a level that is dangerously high above the ship's center of gravity. These holes must be plugged at once. Give the holes at the waterline or on the low side priority (if the ship is listing), and then plug the higher holes.

The same methods and materials used to repair holes above the waterline are also used, for the most part, in the repair of underwater holes. The repair of underwater holes tends to be more difficult. Therefore, any Damage Controlman who can repair underwater damage must certainly

be able to repair similar damage above the waterline. For this reason, most of the discussion in this chapter will deal with the repair of underwater damage.

FACTORS AFFECTING UNDERWATER REPAIRS

The two main factors that make it difficult to repair underwater holes are the pressure exerted by the water and the relative inaccessibility of the damage. The difficulties caused by water pressure are often exaggerated. Actually, a hole 7 feet below the waterline is only subjected to a water pressure of about 3 pounds per square inch.

Figure 7-1 shows the flooding effect of unplugged holes and of the same holes after inserting simple plugs. The volumes of flooding water are given in gallons per minute. The number of electric submersible pumps required to handle the flooding is also shown. It should be obvious that prompt plugging of holes is desirable. It can save the ship, it releases pumps for use elsewhere, and it saves wear and tear on the pumps that are in use. Note that the pump capacities used are considerably under the rated capacity, usually 180 gpm. However, if the pump strainers get clogged with debris, the actual capacities may be much less than the rated capacity.

The greatest difficulty in repairing underwater damage is usually the inaccessibility of the damage. If an inboard compartment is flooded, other compartments will flood if you open doors or hatches to get to the actual area of damage. In such a case, it is usually necessary to send a crew member wearing a shallow-water diving outfit down into the compartment. The repair work may be hampered by tangled wreckage in the water, the absence of light, and the difficulties of trying to keep buoyant repair materials submerged.

^{PLUGGING AND} PATCHING HOLES

^{The procedures} discussed here for plugging ^{and patching holes} are intended for emergency use. They are temporary repairs that can be done to keep the ship afloat while it is in action. In most cases, they do not call for elaborate tools or equipment. They involve principles that can be applied when using wooden plugs, prefabricated patches, or other readily available materials.

There are two general methods of making temporary repairs to holes in the hull: put something in it or put something over it. In either case, the patches will reduce the area through which water can enter the ship or through which water can pass from one compartment to another.

Plugging

The simplest method of stopping up a fairly small hole is to insert some kind of plug. Plugs made of softwood, such as yellow pine or fir, are quite effective for plugging holes up to about 3 by 3 inches in size. Sometimes you may use these plugs to plug larger holes as well.

The plugging kit consists of the following items: l

A canvas bag, with a carrying strap, approximately 30 inches deep and 12 inches in diameter

Softwood plugs; a minimum of 10 plugs in various sizes from 1 inch to 10 inches in diameter l

Figure 7-1.-Flooding effect comparison; unplugged holes vs. partially plugged holes.

• Five pounds of oakum or rags

• One hatchet

• One cold chisel

• Onmetal caulking iron

• Wedges made of softwood; a minimum of eight wedges, 2 inches by 4 inches and 12 inches long

• One maul or sledge

• One hammer, a minimum 2 pounds in weight

• One crosscut handsaw for cutting wood

The plugs and wedges may be used individually if they fit the hole. Often, however,

it is best to use a combination of conical, squareended, and wedge-shaped plugs to make a better fit in the hole. One such combination of plugs is shown in figure 7-2.

It is best to wrap each plug with lightweight cloth before inserting it. The cloth tends to keep the plugs in place and fills in some of the gaps between the plugs. In most cases, plugs will not make a watertight fit. However, you can substantially reduce the rate of leakage by using the plugs and then caulking the remaining leaks with rags, oakum, and smaller wedges. Square-ended plugs tend to hold better than conical plugs in holes located in plating that is one-fourth of an inch or less in thickness.

Most wooden plugs are inserted from the inside of the ship. When plugging a hole in this manner, you must contend with the metal edges

that are protruding inward. You normally will not have this problem when plugging a hole from the outside of the ship. However, plugs on the outside of the ship cannot be tended easily nor will they hold very well over an extended period of time. If it is necessary to insert the plugs from the outside of the hull, fit the inboard ends of the plugs with screw eyes. A line running from each screw eye and secured to a solid structural member inside the ship will help to keep the plug in place.