METHOD OF CONSTRUCTION OF CONCRETE SHIPS. 21 



Slope of launching ways, 1^4 inch to the foot. 



Slope of trigger ways, i^ inch to the foot. 



5 triggers forward and five aft. 



35 launching ways. All ways spaced 8 feet 6 inches on centers. 



Launching ways, i8 inches by 30 inches hard pine. 



Packing (mostly), 12 inches by 12 inches hard pine. 



Bearing stress on grease, 2)/^ tons per sqvtare foot. 



Trigger rope, i inch diameter Manila hemp. 



Launching grease: 



i/16-inch stearine on slides and ground ways. 



3/16-inch launching grease on slides and ground ways. 



^-inch launching grease between packing and ways. 



At the date of writing, the Fleet Corporation has launched three 7,500 D. W. T. 

 concrete tankers and one 3,500 D. W. T. cargo ship by the side-launching method 

 described. In addition, one each experimental 3,000 and 3,500 D. W. T. cargo ships 

 have been launched endways. All six launchings have been thoroughly successful 

 and without accident or damage to the hulls. 



PAINTING. 



Both the exterior and interior of all ships are painted. 



The disintegration of reinforced concrete in sea water is due to the penetration 

 of the water into the pores of the concrete in the submerged portion of the con- 

 crete, its absorption by capillarity into the air-exposed portion and the evaporation 

 of the water with a resulting concentration of sea salts, causing an accelerated cor- 

 rosion of the embedded reinforcement which splits and spalls the concrete. 



The effectiveness of the protection to the steel provided by the rich concrete 

 mixture used in ship construction is unknown. 



As a precautionary measure, it was deemed wise to apply a paint coating to 

 the exterior below the water-line to reduce penetration, and above the water-line 

 and on the interior surfaces to reduce evaporation of any water which may be ab- 

 sorbed by capillary action. In the tank ships it was also deemed advisable to apply 

 an impermeable semi-elastic oil-proof coating to the inside surface of all oil com- 

 partments. The bottom of a concrete ship will foul to the same extent as a steel 

 ship unless it is protected ; therefore an antif ouling paint was also applied. 



Many tests have been made and a large number of different paint combinations 

 have been tried, but experience has not been sufficiently extensive to fully demon- 

 strate their value. It would appear' that the bituminous paints are the more satis- 

 factory where continuously exposed to water. Following is a brief description of 

 the various combinations now being used on the different surfaces. 



All paints except the bituminous coatings were applied by air brushes. 



It was originally intended to apply two priming coats of a y]^ per cent solu- 

 tion of magnesium fiuosilicate over all surfaces of the hull. The purpose of these 



