88 COMPARATIVE TESTS OF BILGE KEELS AND A GYRO-STABILIZER 
crests on these sinuous curves. In other words, one swing comprises the motion 
from port to starboard or vice versa. 
5. The model was next rolled with and without bilge keels and with the gyro- 
stabilizer in waves. For this purpose it was held broadside to the waves by single 
head and stern lines made fast to the model at the water-line close to the longi- 
tudinal rolling axis. The height and period of the waves could be controlled within 
limits and could be so adjusted as to produce marked rolling. The results of these 
tests are shown on Plate 34. In the same system of waves the bilge keels reduce the 
arc of roll from 26.4 degrees to 9.6 degrees, or about two-thirds, while the gyro- 
stabilizer reduced it very quickly when cut in, from 34 degrees to 3 degrees or to 
about one-eleventh of the uncontrolled roll, which was somewhat greater than in 
the two preceding cases because of better synchronism between the waves and the 
natural period of the model. 
6. The model was then tested in waves approaching half the period of the 
model, the resulting records being shown on Plate 35. With the bilge keels in place, 
when the wave length was shortened so that the rolling was no longer syncronous the 
model stopped rolling almost entirely, and no other wave period could be found that 
would induce rolling to any extent as the typical record on Plate 35 illustrates. 
When the bilge keels were removed, however, it was easy to find a period of wave in 
the vicinity of the half period of the model that would cause very heavy rolling. 
The angle rolled through was so great that it was necessary to use a shorter arm for 
the pencil of the gyroscopic roll recorder, thus changing the scale for angle of roll 
on the records and running up to at least 48 degrees as shown on Plate 35. The 
last record on Plate 35 shows the effect of the gyro-stabilizer. When cut in, the 
stabilizer almost instantly cut down the maximum roll to about 2 degrees. 
7. As it was apparent from the preceding tests that the roll-quenching capacity 
of the gyro-stabilizer was more than ample for the model, an investigation was next 
made to determine its performance, without bilge keels, in higher waves, the higher 
waves being obtained by increasing the eccentricity of the wave maker while at- 
tempting to keep the period of the wave such as to produce maximum rolling. On 
Plate 36 are shown the rolling records for different waves. In the following table 
is given the eccentricity of the wave maker and the corresponding height, length 
and period of the waves for the ship. 
TABLE I. 
Approximate dimension of wave for ship 
Wave-maker 
eccentricity, inches 
Height, feet Length, feet Period, seconds 
4 11.9 1,391 16.5 
5 13.5 I, 409 16.6 
6 17.3 1,275 15.8 
7 19.5 1,357 16.3 
