The 1 4- inch-thick Plexiglas— ^ obserTation 

 windows are set in polysulphide rubber-base 

 cement and bolted to the window frames; large 

 washers separate the bolt heads and the Plexi- 

 glas. The upper six windows are centered 6 

 Inches below the water surface. (Prior to modi- 

 fication these were the only windows in the cham- 

 ber.) Below the upper windows a hexagonal steel 

 flange, which increases the diameter of the cham- 

 ber to 47 inches, is welded perpendicular to the 

 cylinder. The frames of the six middle windows, 

 facing horizontally, and of the six lower vk-indo»"s, 

 which are inclined ai a 35" angle, are welded to 

 the periphery of the flange and to the cylindrical 

 lower section of the chamber. Three 2-inch pipes 

 ihat extend from the inside edge of the flsinge 

 ;;-'- to the lower section of the cylinder proTide 

 i.:.:;ional stiffening. 



LAvas invTt S&A. 



-»t>:_CT3s rrrr 



The 12-foot -square raft is strongly biiilt to 

 withstand rough handling at sea. The frame is 

 coBstrncted erf 4- by 14-inch and 4- by 4-inch 

 timbers lap-Jointed and through-fastened with 

 5/s- by 15-inch galranized steel bolts. Four 

 5/8-inch steel tie-rods further stiffen the struc- 

 ture. This frame Is decked with 2- by 12-inch 

 planks fastened with galvanized nails. Ten 55- 

 gallon drums beneath the deck provide buoy- 

 aiscy=- . They are held in position between the 

 tie-rods gnri the side timbers by rope lashings 

 and steel straps. Centered in the deck Is a 50- 

 iach-sqoare aperture for the observation cham- 

 ber. 



As^^Ttsmjiv^ Kcr 



The chamber isf^ - - steel, 



gaivanized inside a- t i with 



black asphalt paint. It is 9.5 feet long, has a 

 miaimum diameter of 28 Inches, and extends be- 

 low the raft to a depth of 6.0 feet beneath the 

 water surface. Four legs, strengthened with 

 gussets and welded to the chamber, are bolted 

 to four 5/8-i3!Ch galvanized steel stnds in the 

 timbers around the deck aperture. When bolted 

 in position, the chamber projects 3 feet above 

 the deck. 



— sTED-snure 



^re 2. — Plan of the Nenue. 



irr=r "=sr crirzs 3£sr zsi& iSiaac or iiSisaii 

 severs! mocificarioas were as.de. Origiaally 

 oaly six 53- gallon dru ms isere -jsed. Foor addi- 

 cioasl dnass iacreased t'ae freeboard and kept 



tbe deck drier. 



~ Trade sasie referred to in this pofalication 

 does not iroly endorseaenr of conaercial pro- 

 duct. 



