190 MACHINERY AND TRIALS OF THE PASSENGER SHIPS 
The boilers are of the Babcock & Wilcox regular marine type having 42-inch diameter 
steam drum and 2-inch O. D. tubes. The superheaters are of the Babcock & Wilcox type 
mounted on top of the boiler back of the steam drum. The superheater consists of two hori- 
zontal headers, mounted horizontally one above the other at the outboard side of each boiler. 
A double row of U-shaped tubes extending across the boiler has its ends expanded into the 
two horizontal headers. The boiler is so baffled that the gases of combustion pass ver- 
tically up through the boiler tubes at the rear end of the boiler, then over the superheater 
tubes, then down a second pass through the boiler tubes, and turning again go up a third 
pass to the uptake and stack. ] 
It is not intended to give a full description of all the parts of this machinery, and it 
would be very wearisome to discuss all the various auxiliaries which make up the equipment. 
They are, therefore, presented in the table on pages 191 and 192. 
The arrangement of machinery in outline, together with the lead of the shafts and posi- 
tion of the propellers, is shown on Plate 55. 
The distance from propeller tips to hull plating at the nearest point is 2 feet 51% inches. 
The model for the vessels of this class was towed in the tank at Washington, D. C., 
under various conditions, and Plate 56 shows a copy of the curves of the effective horse- 
power and speed developed from these tests. The curves given are for hull with rudder. 
Some time later it was decided to make further tests on self-propelled model and the 
results of these are also given on Plate 3. On this test, the propeller represented those which 
were fitted on the American Legion. These are built propellers, three-bladed, with cast-iron 
bosses and bronze blades, 17 feet diameter, 18 feet 6 inches pitch, with a developed area of 
84.4 square feet, and projected area of 71.499 square feet, and were intended for about 110 
revolutions at full power. 
The curves estimated from the tests show the shaft horse-power, revolutions per minute, 
and propulsive efficiency at 24 feet, 30 feet, and 36 feet draught. There have been added, for 
comparison, the estimated shaft horse-power, revolutions per minute, and propulsive efficiency, 
at 24 feet draught for the propeller of the President Pierce. These are shown in dotted lines. 
It has been noted that the propellers on the President Pierce vary from those used on the 
self-propelled model, the revolutions having been increased from 110 to 125 in order to 
obtain a more reasonable reduction gear. At the same time, the substitution of a solid wheel 
for a built wheel, and the machining of the driving faces, made the efficiency of the two 
wheels practically identical so far as could be calculated. 
The sea trials of the President Pierce were carried out at 24 feet draught, the lowest at 
which the models were tested and the easiest at which to ballast the ship, with the loads 
arranged so that at the high runs of the standardization trial the draught would be as near 
as possible to the 24 feet and as near as possible to an even keel. The weather on the runs 
was good with very slight sea and light wind, so that there was no need to consider any cor- 
rection from these conditions. The runs were made on the standard mile off the Delaware 
breakwater, and that course is rather shallow for a vessel of this size and speed, so there is 
probably some interference at the high runs. The depth on the course varies from 23 to 
25 fathoms, but the straight way leading up to the mile buoy at each end is considerably 
shallower, being from 19 to 22 fathoms at the north end and from 15 to 21 fathoms at the 
south end, and this again may have caused some interference so that the speed obtained is 
probably not quite so good as it would have been on a deep sea trial. 
