The object of this report is: To determine by fabrication and test of test specimens of a built-in flotation compartment a method of sealing seams and joints in riveted light-gage sheet-metal construction; to determine which sealing compounds were adaptable, and a practical method of applying the sealing compounds to the riveted joints. To determine whether it is reasonable to expect absolute watertightness in flotation compartments, and to determine a reasonable test for tightness. To study a type of fitting suitable for vent-line bilge-pump connections, etc. Flotation compartments can be made watertight and airtight if the type of structure is adaptable to being sealed with tape impregnated with sealing compound. The technic of assembly and experience of mechanics in fabricating this type of structure contributes materially in making tight joints. A reasonable test pressure is one-half pound per square inch.