88 THE APPLICATION OF DYSON’S METHOD 
which accounts for the difference in horse-power between the estimate and that obtained 
on the trial. Unfortunately indicator cards were not taken on the mile run, but were taken 
after the same. The average power was 6,155 and average revolutions 102.75. Assuming 
3 
the power to vary as the cube of the revolutions we have 6,155 x ( 22475 | = 6,540, 
102.7 
which is used as the indicated horse-power on the mile course. If this figure (6,540) was 
used in the calculations for slip in place of the estimated power, Ra would have been 102.8 
in place of 101.8. 
GRouP 3. 
When the wing shafts are carried in bosses, the basic slip seems to be affected if the 
bosses are horizontal or nearly so, as will be shown in Problem 12. 
Problem 11, Plates 25 and 26.—Unfortunately, no trials were run on these ships at the 
designed deep draught of 30 feet. The model was tested at three draughts with model 
propellers, the results of which are used in Plates 25 and 26. While the powers check 
very closely in all three cases, the estimated revolutions at 36-foot draught do not 
agree with those obtained from the model test. As this draught (36 feet) is four times the 
height of the center of propeller above the base line, this might be considered as a deep- 
draught vessel with propellers carried as deeply as possible, which condition is not covered 
in Admiral Dyson’s latest work. A correction should be made for obtaining the basic slip. 
The writer is not prepared to say just how this should be made, but two ways are possible; 
first, taking the slip block coefficent and basic slip at a lighter draught, or second, by using 
a line on the block coefficient chart passing through the lower left-hand corner of the chart 
and cutting the right-hand side somewhere above line X. The slip block coefficient would 
then be less and the basic slip greater than what it would be by using line X. 
A trial was run on a ship similar to this but fitted with different propellers, the re- 
sults of which are shown on Plate 26. It will be noticed that, while the revolutions agree, 
there is some difference in the power. This was caused by the run being made on the 
Delaware Breakwater Course. The lack of deep. water affects the power but does not seem 
to vary the revolutions for given speeds. This was shown hy tests conducted by the U. S. 
Navy on the battleship Michigan, which was run over the Rockland, Provincetown and 
Delaware Breakwater courses. While the revolutions for various speeds were practically the 
same on all the courses, the power varied considerably. As the draught and range of speed 
of the two ships are practically the same, it would be safe to consider that, had this ship been 
tested in deep water, the power developed would have been very close to that estimated, 
while the revolutions would be the same as those obtained on this trial. 
The propeller shafts of both model and ship were carried in bosses set at about 32° 
with the horizontal plane, the intersection of which with the hull was probably parallel or 
nearly parallel with the stream lines. 
Problem 12, Plate 27—The angle between the bosses and the horizontal plane on this 
ship was about 10 to 15° which, as will be seen in the calculation, seems to affect the basic 
slip. The revolutions were first calculated using the value for slip block coefficient as given 
on line X, then using line Y. In the former case the calculated revolutions were greater 
and in the latter they were less than those obtained on the trial. By using a value between 
these two, the calculated Ry, worked out almost the same as the actual Ry. On account 
of lack of data, the value of K cannot be determined, but an estimate was made of the ef- 
