Patching

Box patches are effective for use over holes that have jagged edges projecting inboard. View A of figure 7-3 shows a typical metal box patch;

Figure 7-2.-Combination of plugs used to plug a hole.

_{Figure 7-4.-Application of a hinged plate patch.}

Figure 7-3.-Application of a box patch. 7-6

Figure 7-5.-A. Types of hook bolts. B. Use of hook bolts in applying a patch.

view B shows a metal box patch held in place by shoring; and view C shows a metal box patch welded in place over a hole that has jagged edges.

A hinged patch is designed for use over relatively small holes. This patch has no vertical support to hold it in place. Figure 7-4 shows a hinged plate patch before, during, and after installation.

A hook bolt is a long bolt that is usually fabricated from round steel stock. Hook bolts come in a variety of diameters and shapes. The head is shaped so that the bolt can be hooked to the plating through which the head has been inserted. Figure 7-5 shows T-shaped, L-shaped, and J-shaped hook bolts and how the hook bolts are used to apply a patch. The long shanks are threaded and are provided with nuts and washers. Wood (or sometimes steel) strongbacks are used with hook bolts.

To use a hook bolt, insert the head end of the bolt through the hole in the hull. Rotate or adjust the bolt until it cannot be pulled back through the hole. Slide a pad or gasket that is backed by a plank or strongback over the bolt. Secure the patch by tightening the nut. Generally, these bolts are used in pairs. Hook bolts can be used with a variety of patches and in various combinations.

The folding T-shaped hook bolt has a hinge where the shank joins the crosspiece. This bolt can be folded and inserted through a small hole.

When the bolt is pulled back, the crosspiece catches on the hull plating. By using this bolt, a crew member standing inside the ship can put a patch on either the inside or the outside of the ship. By using a retaining line on the bolt, a strongback and a pillow can be threaded over the line and the entire patch folded and placed through the hole. When the line is hauled in, the patch fits against the ship. The patch can be re-adjusted to give a tighter fit. It is also possible to push the pillow and plate over the shank inside the ship to make an inside patch. Nuts and washers are provided to hold and tighten a patch; often large wing nuts are used. Figure 7-6 shows one way in which a folding T-shaped hook bolt can be used to secure a patch.

Figure 7-6.-One method of installing a folding T patch.

Ordinary feather pillows have a tendency to ball up when they are wet and do not provide a uniform surface when used to patch holes. For this reason some ships carry special pillows (fig. 7-7) made of canvas and oakum.

You will frequently find it necessary to improvise patches by using whatever material is handy. This calls for skill and a certain amount of imagination. Hinged or folding prefabricated patches are usually the easiest to use, and in many cases, they are the most effective. But if they are not available, you will need to improvise patches.