544. Edward VY. Lewis and John P. Breslin 
The complication of a controllable pitch propeller was not considered necessary; how- 
ever, for backing and for emergency propulsion, small auxiliary screws were assumed driven 
by medium-speed diesels. The speed that can be achieved with this propulsion will be 
around 5 or 6 knots. 
For these tests the following characteristics were selected. 
Hull-Form Coefficients — Length/beam ratio = L/B =:7.0; submergence beam ratio = 
h/B = 1.25 (to centerline); prismatic coefficient = Cy = V/(7/4) B2L = 0.650; wetted surface 
coefficient = K, = W.S./7BL = 0.774. 
Ogive-Strut Coefficients — Thickness/chord ratio = t/c = 0.167; submergence/chord 
ratio = h/c = 1.30; c/L = 0.139. 
Machinery — Main engines: GE converted aircraft engines, type MS240B, MS240A, 6000 
rpm; reduction gears: double reduction, epicyclic type, small with low weight (estimated on 
the basis of Timmerman second reduction gears); overall fuel consumption: 0.55 /SHP-hr at 
V = 45 knots and 0.58 /SHP-hr at V = 20 knots. 
Propulsion — For this study the top speed was chosen at 45 knots and the cruising 
speed at 20 knots. The propeller and propulsion characteristics chosen (not necessarily 
optimum) were as follows: 
A = 6000 A = 3000 A = 1500 A = 750 
Propeller diameter Dalhelsy ate 16.8 ft 13.4 ft 10.0 ft 
Shaft rpm 200 250 300 400 
Propeller efficiency 
at 45 knots 74% 75% 76% 76% 
Assumed hull 
efficiency 140% 120% 120% 120% 
The appendage resistance allowance chosen was 10 percent in all four cases. All propellers 
were checked for avoidance of cavitation. 
Weights 
Assumed hull, machinery weights, and other data are shown in Table 2. 
For any vehicle, whether for military or commercial service, the basic characteristics 
of interest are speed, range, and payload. Various types of plots can be prepared to show 
the relationship among these variables for different craft. However, for ASW purposes the 
particular need seems to be for a top speed between 45 and 50 knots and a cruising speed 
between 15 and 20 knots. Hence, in the present study fixed speeds have been assumed and 
trends have been determined of range versus payload for a family of vehicles of different 
sizes. The results are shown in Fig. 11. 
The plot shows that for fixed speed and size, the payload available for weapons, detec- 
tion gear, etc., varies inversely as range. And for any given range, the larger the ship the 
greater the payload must be. To be more specific, it appears that a 1500-ton craft for 
