TABLE 1 



Model Constants 



Length 



136 inches 



Beam 



16 inches 



Draft 



6.4 inches 



Displacement 



316.6 pounds 



Midship Area Coefficient 



0.964 



Load Waterline Coefficient 



0.667 



Prismatic Coefficient 



0.655 



Blocl< Coefficient 



0.632' 



6.40 in 

 DWL 



Dead Rise Angle-C-ZS 



Figure 1 - Body Plan of the Model 



The model was constructed as light as possible (about 80 pounds) and no attempt was 

 made to ballast it to design displacement. This reduced to a minimum the inertia loading of 

 the force balance during oscillation and allowed greater accuracy in determination of hydro- 

 dynamic force components. 



TEST EQUIPMENT 



The mechanical oscillator is mounted on the carriage over the deep-water basin. A 

 d-c motor drives a Scotch yoke through an intermediate flywheel and 2-step gear reducer. 

 The Scotch yoke converts rotation to linear motion and causes a vertical rigid strut to per- 

 form simple harmonic heaving oscillations. The oscillation frequency is varied by altering 

 the motor speed and gear box setting, while oscillation amplitude can be altered by mechani- 

 cal adjustment of the Scotch yoke mechanism. 



A six-component strain-gage balance (Figure 2) is attached to the bottom of the oscil- 

 lating strut and the model is attached to the balance. At midstroke of the oscillator the mo- 

 del is at the specified draft, keel parallel to the water surface, and the center of the sym- 

 metrical model is below the oscillating strut. 



The six-component balance is positioned so that it directly measures lift and drag 

 force and pitching moment about the center of the model. These three components are sensed 

 by 4 active-arm bridge circuits and are recorded on a string oscillograph. In addition, a 

 Schaevitz differential transformer provides a record of the heaving displacement. A sample 

 record is shown in Figure 3. 



