232 THE PROPELLING MACHINERY OF THE U. S. S. LEVIATHAN. 



These repaii's progressed slowly, but the conditions under which the men 

 were working were exceptionally trying. It was in midsummer, and only two men 

 could work in the cylinder casing at one time. They had to work doubled up, with 

 their knees touching their chins, because above them was the rotor with its rows 

 of jagged blades. It was not possible to move this out of the way, and the men 

 were also breathing continuously the fumes from the electric arc. 



To repair the top half casing, the rotor was lowered and the work was again 

 done in very hot and close quarters. 



Whilst the electric welding was in progress, practically no other repair work 

 could be carried out, owing to the glare from the arc blinding anyone standing by. 



After this work was completed the casing was tested under water pressure to 

 about loo pounds per square inch, and found to be practically watertight. 



Before the new dummy cylinder could be fitted it was necessary to grind down 

 the weld patches until they projected only about ^ inch above the faces of the ad- 

 joining wall, and the dummy cylinder castings were notched out to fit over the 

 patches. 



All the damaged reaction blades were replaced; this amounted to about 8,000 

 new blades and packing sections, and the turbine was closed up on October 31. 



Engine-Room Ventilation. — Two large fans are arranged at the after end of 

 the aft engine-rooms and supply air through ducts to the main engine-rooms. 



Two of the Howden forced draught fans for the boiler-rooms are installed at 

 the forward end of the main engine-room and ventilate the hottest part of the ma- 

 chinery spaces. 



To ventilate the closed-in spaces under the platform of the main engine-room, 

 the floor forms an air duct about 10 inches deep, and cooling air is circulated to 

 various parts around the turbine bearings, etc. This method also helps to keep the 

 working platform cool. 



Boilers. — The boilers are arranged in four watertight compartments, three 

 compartments having four groups with three boilers per row athwartships, whilst 

 the forward compartment contains ten boilers, making a total of forty-six boilers 

 in all. 



Coal bunkers are arranged in the wings at the sides of the boilers, separated 

 by watertight compartments. 



The boilers are of the Yarrow type, having one steam drum connecting through 

 two groups of tubes to the lower drums, each boiler having three furnaces. The 

 working pressure is 235 poiinds per square inch gauge, and the heating surface of 

 the generating tubes is approximately 210,000 square feet. They are designed to 

 work with Howden's forced draught, four large breast fans driven by compound 

 reciprocating engines supplying the air. 



The boilers were found to be in fair condition, and only two required re-tubing. 



The brickwork was renewed in a large number, and it was also found neces- 

 sary to install new fire bars, so as to allow more air to pass through the fires. 



The methods used for draining the steam lines from the boilers were very poor, 



