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Working Conditions and URING a heavy northeast D wind which kicked up consid- erable sea in the slip of the Liberty Shipbuilding & Transportation Co.'s shipyard at Cleveland, a hole was stove in the port side of a rein- forced concrete car float, built for the embarkation service, war depart- ment, which had been launched a few days previously. The hole, located just below the lower strake of the wood fender and about 53 feet from the stern of the boat, was entirely below the waterline. It was caused by the parting of a breast mooring line, allowing the car float to surge against a wooden raft moored between © it and another concrete car float. The raft was constructed of 12-inch pile butts with a 2-inch plank deck. One of the pile butts extended beyond the ends of the others, and it was this projecting end which punched through the skin of the ferroconcrete car float when the latter was thrown against it with terrific force. The deadweight of these car floats is about 1500 tons, so it.is not difficult to imagine the impact developed which would doubtless have punctured either a wood or steel craft. The compartment in which the hole was located soon filled with wa- ter which listed the float about 4 degrees to port. There was no dan- ger of the craft sinking as these car floats are provided with watertight bulkheads. After studying the situation it was decided first to locate the hole ac- curately and determine the extent of damage to the surrounding con- crete. With this in. mind, the out- board compartments on the starboard side and forward of the compartment in which the hole was located were filled with water. An _ additional weight of 30 tons of rail was also placed on the deck at the starboard bow. This listed the boat about 12 'degrees to starboard and _ brought the hole above water. That is, the bottom of the hole was just awash, as shown in Fig. 4. A thorough exam- ination of the puncture and the sur- rounding concrete was made and it was found that the break was in the 3%4-inch reinforced concrete skin be- t The methed described in this. article was devised by the author, an engineer connected with the Liberty Ship Building & Transportation Co., Cleveland. The repairs were carried out under his supervision. low to Patch Holes in A Wooden Caisson Was Built Over the Hole to Four Applications of Cement Applied tween frames 38 and 39. At the cen- ter of the hole, the reinforcing rods were bent out of line about ¥4-inch. The hole was about 3 feet long and 18 inches wide. The con- crete skin was shattered and cracked for a radius of about 2 feet sur- rounding the hole, but no damage was done to the concrete frames or side beams. It was evident that in order to cut away the damaged concrete and patch FIG. 1--CAISSON IN PLACE AT THE SIDE OF THE BARGE the hole, protection from the rolling of the boat and consequent wash of the seas had to. be taken into- consid- eration. . To provide for this condi- tion a timber caisson was built as shown in Fig. 2, and lowered into position over the hole. All seams were caulked and holding-down bolts drawn tight, after which the cofferdam was pumped dry with a 3-inch steam syphon.. A comparatively dry work- irg chamber or caisson was thus pro- vided .and. repairs to the hole were started. The cofferdam is. shown. in Fig. 1. which also shows a 4-inch cen- trifugal pump. This was set up -for emergency use in case of failure of the syphon to keep the cofferdam dry. 284 Lips Afford Dry By C. D. C. Wilson The area of the patch after all cut. ting out was done, assumed the shape shown in Fig. 4. Additional vertical stee| was threaded in between the horizon- tal reinforcement in order to provide a closer mesh for the binding of the concrete. A wooden form was put in place on the outboard side of hole, and after thoroughly cleaning all con- tact surfaces with compressed air and water, a concrete patch was put on by the gun method, using a mixture of the same proportions as was used in fabricating the rest of the boat. Four applications were necessary to complete the patch. This was due to the rolling of the boat which pre- vented a heavy application at one time. It required four days from the date of puncture to complete the patching. The outside form was removed two days after concreting was finished and two coats of waterproofing material composed of magnesium fluo-silicate "were brushed on the outside of the patch. This same mixture had been applied to the entire hull and deck of this car float before launching. One week after repairs were com- pleted the boat was brought to an even keel by pumping out the water in the starboard compartments. Wa- ter pressure was kept from the patch, however, by pumping out the coffer- dam until the concrete was two weeks old. The cofferdam was then removed and the wooden rubbing strip, which had been taken off to allow the plac- ing of the cofferdam, was reset. No seepage of water has taken place around the edges of the patch, and there is no leakage through the patch. This is believed to be the first at- tempt to patch a concrete hull where the damaged section has been below the water line and the company is confident that regardless of the lo- cation of the hole, it can be expedi- tiously and economically repaired. Engineers of this concrete yard state that, such repairs can be made with less delay and expense than with a steel or wood hull. To illustrate. Let it be assumed that this hole had been stove in the bottom in- stead of the-side of the car float. The- particular compartment in which the puncture occurred would have filled with water, the bulkheads con- fining it -to one .compartment. Thus the craft would have still remained