High Speed Displacement-Type Hulls 587 
a correlation factor of 1.10 and a measured model wake fraction of 0.05 gave good agreement 
with the measured power, particularly at higher speeds. 
The results of these two trials suggest that a ship-model power correlation factor of 
1.10 is reasonable; further trial] data are needed to confirm this estimate. 
RUNNING PERFORMANCE 
Effect of Spray Strips 
At speed/length ratios of 3.5 and above (F, 2 1.2), a round-bilge displacement-ty pe 
hull develops a troublesome bow wave. This occurs at about 25 to 40 percent of the length 
aft of the bow, and for a 100-foot vessel can be 4 to 5 feet above the still water level. 
Unfortunately, this wave often is covered by a fine spray film which starts at the bow 
profile and in still water clings to the hull above the main wave profile. In bad or windy 
weather this film breaks away from the hull as spray which can cause considerable wetness 
of the afterstructure. 
Model experiments were made with spray strips in an effort to combat this effect. On 
the form shown in Fig. 23 a strip 1 inch x 1 inch (for a 100-foot vessel) was fitted at about 
3 feet above the still water line from the bow to midships. This prevented the film rising to 
the top side of the model, and enabled the speed to be raised from 30 to 42 knots without 
serious trouble. 
Fig. 23. Model 2084; 100 feet x 16 feet x 5.48 maximum 
draft x 100 tons 
It has been found that spray strips either reduce the resistance of a model or have no 
measurable effect. Model trim is increased by about 0.5 degrees at the highest speeds. 
