the repair may involve appreciably more restraint, with less latitude for proper welding and direction sequence, than for new construction. Careful planning is essential.

(c) Cracks. In general, material should not be removed in crack repairs unless the crack has opened up to a large extent, or the crack location prevents the necessary access for producing sound, full penetration welds, or there is definite evidence of deterioration or poor quality of the fractured plate. Cracking as such does not indicate that the steel quality is inferior to other parts of the structure. In repairing

cracks which do not involve steel replacement the following should be observed:

(i) Locate the ends of the crack, and at least one plate thickness beyond the end drill a hole to prevent its extension. The diameter of the drilled hole should be about the same as the plate thickness. Then, V out the crack to an accepted edge preparation for plates of the particular thickness involved.

(ii) After V-ing out, if a crack has a root opening too wide for closing with the first bead, do not draw the edges of the plate together by means of the steamboat ratchet preliminary to welding. Instead, build up the V surface with light beads, until a standard joint prepa ration is obtained, then the joint is ready to weld up as usual.

(iii) Where the crack in the plating crosses stiffeners, framing or girders, the welds connecting these members to the plating shall be released. This shall be done by chipping out for at least a foot of weld on each side of the crack before welding up the crack. In way of gunwale or hatch side assemblies, it may be desirable to increase the length of release.

(iv) New butts may be provided locally in framing members where the crack in the plating crosses over the members. If such butts are welded after

the plating or poor accessibility exists, the butt in the frame should be scalloped out adjacent to the plating.

(v) The use of pre-heat is advantageous in locally increasing resistance to cracking during repair welding and in subsequent service. Where used, preheat temperatures should be at least 150° F. with temperature maintenance during the weld cooling cycle. Pre-heat may be used for the entire crack repair, including framing, or in selected locations, such as in vicinity of crack ends; in welding across framing which is unbutted, or in which local butts have already been welded; or in welding framing butts after the crack in plating has been welded.

(vi) Except where redesign of critical details, such as hatch corners, are concerned, the addition of a doubling plate locally to locally to cover and ostensibly strengthen a welded crack shall not be permiti' The abrupt change of section, resulting from such an installation with its additional local welding, may do more to promote than prevent future cracking in the region. Cracking is primarily an indication of design or welding notches rather than structural inadequacy. It should be recognized that, if a notch exists in a vessel, the vessel will be less susceptible to cracking when its over-all working stress level is reduced. Installation of long doublers for this purpose is satisfactory. However, this is generally a fairly extensive alteration and should not be undertaken without prior plan approval covering the work involved. Such doublers generally extend longitudinally over at least the midship half length of the vessel and are positioned at symmetrical locations about the vessel's girth.

(d) Protection against weather. When possible, repair welding should be avoided in cold weather, particularly when the temperature is below freezing. However, the effects of cold weather may be minimized by preheating to

about 150° F. before welding. Heavy sections should be preheated prior to making a repair, regardless of the ambient temperature. A tent or shelter should be used to protect the welding operator and the work from bad weather, as well as the arc from strong winds. A tent or shelter should always be used when the temperature falls below zero.

(e) Electrodes. Electrodes shall be suitable to the steel to be repaired. Except where special steels or approvals are involved, the welding electrodes shall conform to the requirements of Paragraph 18, Section 26, of the American Bureau of Shipping Rules for Building and Classing Steel Vessels.

(f) Qualified welders. In view of the importance of obtaining sound welds in repair work, none but the most 'capable welders, qualified by the Coast Guard, the American Bureau of Shipping, or the Bureau of Ships (Navy Department), should be employed thereon.

3-2-5C(6). Cargo handling gear. Repairs or alterations affecting the cargo handling gear shall be accomplished and tested in accordance with the safety standards established in the American Bureau of Shipping pamphlet entitled "Requirements for the Certification of the Construction and Survey of Cargo Gear on Merchant Vessels, Etc."

3-2-5C(7). Reporting of structural failures.

(a) Form CG-2752. Structural failures shall be reported on Form CG-2752, Report of Structural Failure of Inspected Vessel. Supplement this report with photographs and large-scale sketches emphasizing the point at which the frac ture started. Mark the sketches and photos clearly with ship's name and with reference points, such as frame numbers, strake of plate, deck or shell, port or starboard side, etc. See Figure 1. Use arrows or lines to point out the fracture and particularly its starting

point. No letter of transmittal will be required in submission of the above form. The form shall be signed by the OCMI in the space provided, and shall be stamped on the back with the date of issue and the issuing office. Any necessary remarks should be typed on the back of the form. Where possible, a detailed statement of the amount and location of cargo and of all tankage should be included.

(i) Details of failures required. Details regarding the starting point of the failure are the most important part of the report because all contributing factors are assembled at that point. There is a herringbone pattern on the edge of a fractured plate. The spices of the angles of this herringbone point toward the starting point of the fracture. Figures 2 and 3 are typical fractures. They show how it is possible to trace a fracture back to its source, and how it should be marked. Where it is impracticable to obtain a square view, as shown in Figures 2 and 3, take photo graphs properly angled to show clearly the herringbone pattern on both sides of the starting point. Each such photograph shall include the starting point. Where accurate data regarding "Circumstances Surrounding Failure" quired by by Form CG-2752 are not available, do not leave the spaces blank. Give best available information, such as date damage was found or examined, ports of departure and arrival, a statement as to loading, i.e., either "Ballasted" or "Loaded" and weather, temperature, sea condition, and other pertinent data as it is recorded in the ship's log for the voyage. Where certain information is approximate, label it as such.

re

(ii) Samples of steel. Samples of steel from fractured ships shall not be obtained unless specifically requested by the Commandant. Commandant. If samples are desired, the Commandant (MMT) will forward instructions. Arrangements for

the examination of such samples at a testing laboratory will be made by the Commandant (MMT) and shipping instructions will accompany the request.

(b) Casualties to be reported. The reporting procedure should correspond

the severity of the casualty. (See definitions of classes of casualties in 3-2-5C(7)(c).) The classes of casualties are as follows:

Class 1 casualty. If a class 1 casualty occurs on any vessel, the Commandant (MVI) should be advised by

message or telephone immediately. This report shall give the location and extent of the fracture, so that it can be determined if a HQ representative should be sent to examine the fracture. A sketch showing the fracture, as well as the proposed method of repair, shall also be prepared as promptly as possible and sent to the Commandant (MMT) via air mail. Repairs should not be undertaken until approval of the proposed method of repair, either by a HQ representative, if present, or by the Commandant (MMT). If the fracture and the proposed method of repair can be adequately described

by telephone, telephone approval may be possible. It is not intended to unnecessarily delay the completion of repairs.

(ii) Class 2 casualty. If a class 2 casualty occurs, Form CG-2752 is to be filled out, but the Commandant (MVI) need not be advised by message.

(iii) Class 3 casualty. The Com mandant no longer desires special reports of class 3 casualties.

(c) Definitions. The following definitions have been agreed upon for the purposes of this part:

(i) Structural failure. A structural failure may consist of either a fracture or a buckle occurring under normal operating conditions.

(ii) Casualty. A casualty consists of one or more structural failures which have occurred on the same occasion, on a vessel which is afloat.

(iii) Class 1 structural failure. A class 1 structural failure is any fracture or buckle which has weakened the main hull girder so that the vessel is lost or is in a dangerous condition. For this purpose any fracture more than 10 feet long in the strength deck or shell, shall considered to put the vessel into a dangerous condition.

be

(iv) Class 2 structural failure. A class 2 structural failure is a fracture or buckle which does not endanger the ship but which involves the main hull structure at a location which experience has indicated is a potential source of a dangerous failure. Such locations include the strength deck, inner bottom, side and bottom shell and attachments the reto such as bilge keels and bulwarks.

(v) Class 3 structural failure. A class 3 structural failure is one which does not fall in classes 1 or 2.

(vi) Class 1 casualty. A class 1 casualty is a casualty involving at least one class 1 structural failure.

(vii) Class 2 casualty. A class 2 casualty is a casualty involving at least one class 2 structural failure and no class 1 structural failures.

(viii) Class 3 casualty. A class 3 casualty is a casualty involving class 3 structural failures only.

3-2-5C(8). Buckled plating. Unfair or set-in plating is not uncommon forward. A fair degree of deformation of the hull plates in the forward portion of a vessel ordinarily may be accepted without resulting in serious impairment of structural function. However, for transversely framed ships, buckling or set-in condition of bottom plating, inner bottom plating, and deck plating within approximately the amidships half length can seriously impair the strength of a vessel. In general, the greater the athwart ship extent of buckling the greater the impairment in hull strength. Any appreciable buckle of sufficient athwartship extent to cross a center vertical keel or inner bottom girders is serious.

This buckle should be corrected by fairing and/or replacement of plating and buckled portions of girders. Suitable reinforcement should be provided. In these instances, the Commandant (MMT) shall be advised of the circumstances and proposed corrective measures. A deck buckle of similar athwartship extent should be similarly treated. Buckles of shorter athwartship extent may also require correction, depending upon the depth or height of buckles, the number of buckles, and their relative locations. For instance, several bottom buckles within the same frame space are more serious than the same number of the same size buckles would be if distributed in a haphazard manner fore and aft. Whenever buckling is considered serious enough to cause doubt of the adequacy of the structure, the attention of the American Bureau of Shipping (or of Lloyd's or of Bureau Veritas, if the vessel is classed with either of these societies, rather than with the American Bureau) should be officially invited thereto. If possible an agreement concerning necessary repairs should be reached with the Classification Society. The Coast Guard's and the Classification Society's requirements should be made jointly. If such agreement cannot be reached, the Commandant (MMT) should be contacted by despatch or telephone for instructions, giving the amount, location, and extent of buckling.