4 METHOD OF CONSTRUCTION OF CONCRETE SHIPS. 



32. All tanks are tested up to the light draught line and pointing and patching 

 of concrete is done if found necessary after testing. 



33. The exterior and, if time permits before launching, the interior surfaces of 

 the concrete are painted. 



34. The launching ways are placed in position under the hull, the blocking is 

 changed, and the hull is launched. 



It will of course be impossible in this paper to discuss all the variations of 

 methods which have been employed by each contractor for all operations. Consid- 

 eration will be confined to the more important and general features. 



BLOCKING^ SCAFFOLDING, TRUSSES AND OUTSIDE FORMS. 



All blocking, outside scaffolding, trusses and outside forms are erected com- 

 plete before any concrete is poured, and in some cases before any reinforcing steel 

 is erected. 



The hull as constructed must be supported several feet above the building ways 

 to make the bottom accessible for removal of forms, examination and painting of 

 the outside of the hull and the installation of the launching ways. In steel ship con- 

 struction it is common practice to use heavy timber in the form of blocking or crib- 

 bing for this purpose. There are three fixed stages of support required: — (i) Sup- 

 port during construction ; (2) temporary blocking during the removal of bottom 

 forms and painting; (3) the final blocking on sliding ways for launching. 



In concrete ship construction, since a complete flooring or form supported on 

 joists or stringers must be provided, it was possible, where ways were laid out for 

 side launching, to use either a truss or block and crib type of support. 



At the Wilmington and Jacksonville yards, the bottom form joists are sup- 

 ported at the proper elevation on bents of pre-fabricated trusses having upper and 

 lower chords with vertical posts and diagonal bracing. At Oakland, a similar truss 

 was used, but the floor form sheathing is attached directly to the top chord of the 

 truss. These trusses are placed athwartships. The lower chord is supported upon 

 wedges resting upon the pile caps of the building way, and the upper chord carries 

 the form sheathing direct to the joists of the floor forms, which run longitudinally 

 with the ship. At the forward and aft ends the form joists run athwartships, and 

 longitudinal stringers are provided between trusses and form joists. 



The trusses are divided at the keel into sections and taper from the bilges of the 

 ship toward the keel to accommodate themselves to the sloping way and the dead 

 rise of the vessel. Sway bracing is provided between trusses at regular intervals. It 

 was necessary that the trusses be so spaced that alternate trusses could be removed 

 to permit the removal of the forms, painting of the bottom, and the insertion of 

 the temporary and final blocking. Heavy timber was used in all the yards in the 

 form of blocking or cribbing for the second or temporary support during the re- 

 moval of the forms and the painting of the hull, and also for the final blocking on 

 the sliding ways. 



The Mobile and San Diego yards used heavy timber in the form of blocking 



